Alternating Current Questions

We provide alternating current practice exercises, instructions, and a learning material that allows learners to study outside of the classroom. We focus on alternating current skills mastery so, below you will get all questions that are also asking in the competition exam beside that classroom.

List of alternating current Questions

Question No Questions Class
1 In a step-down transformer the
secondary coil has number of
turns
A. strength
B. less
c. alternating
D. primary
12
2 In series ( L R ) circuit ( X_{L}=R ) and power
factor of the circuit is ( P_{1} ) When
capacitor with capacitance ( C ) such that
( X_{L}=X_{C} ) is put in series, the power
factor becomes ( P_{2} ) Calculate ( P_{1} / P_{2} )
12
3 If ( L, C ) and ( R ) represent inductance, capacitance and resistance respectively, than which of the following
does not represent dimensions of frequency?
( ^{A} cdot frac{1}{R C} )
в. ( frac{R}{L} )
c. ( frac{1}{sqrt{L C}} )
D. ( frac{c}{L} )
12
4 A ( 120 mathrm{V}, 60 mathrm{W} ) lamp is to be operated on 220 ( mathrm{V}, 50 mathrm{Hz} ) supply mains Calculate what value of pure inductance which
would be required so that the lamp runs on correct value of power
A ( cdot 1.174 )
B. 2.348
c. 3.522
D. 4.696
12
5 An alternating voltage ( boldsymbol{E}= ) ( mathbf{5 0} sqrt{mathbf{2}} sin (mathbf{1 0 0} t) boldsymbol{V} ) is connected to a
1 ( mu F ) capacitor through an ac ammeter. What will be the reading of the ammeter?
A . ( 10 mathrm{mA} )
B. ( 5 m A )
c. ( 5 sqrt{2} ) mA
D. ( 10 sqrt{2} mathrm{mA} )
12
6 Assertion: A resistance is connected to
an ac source. Now a capacitor is included in the series circuit. The
average power absorbed by the resistance will remain same.
Reason: By including a capacitor or an inductor in the circuit average power
across resistor does not change.
A. A and R both are true and R is correct explanation of
B. A and R both are true but R is not the correct explanation of
c. A is true R is false
D. A is false and R is true
12
7 A resistance and inductance are
connected in series with a source of
alternating e.m.f. Derive an expression for resultant voltage impedance and phase difference between current and
voltage in alternating circuit.
12
8 A capacitor has a resistance of
( 1200 M Omega ) and capacitance of ( 22 mu F )
When connected to an AC supply of frequency ( 80 mathrm{Hz} ), the alternating voltage supply required to drive a current of 10
virtual amperes is
A. ( 904 sqrt{2} V )
B. 904
D. ( 452 mathrm{v} )
12
9 A pure inductor of self inductance ( 1 mathrm{H} ) is connected across an alternating voltage of ( 115 mathrm{V} ) and frequency ( 60 mathrm{Hz} ). The
reactance ( X_{L} ) and peak current
respectively are
в. 337.12, 0.43 А
c. 377.1Omega, 0.43 A
D. 3.7Omega, 0.42 A
12
10 A light bulb is rated at ( 100 W ) for a
( 220 V ) supply. Find the peak voltage of
the source:
A. ( 111 V )
в. ( 211 V )
( mathbf{c} cdot 311 V )
D. ( 411 V )
12
11 14. The peak value of an alternating emf E given by E = E.
cost is 10 V and frequency is 50 Hz. At time t=(1/600)
s, the instantaneous value of emf is
(a) 10 V
(b) 5/3 v
(c) 5V
(d) 1V
12
12 If the inductance of a coil in 1 henry then its effective resistance in a ( D . C ) circuit
will be
( A cdot infty )
B. zero
( c cdot 1 Omega )
D. 2 ( Omega )
12
13 TC
17. In an ac circuit, the instantaneous emf and current are
given by € = 100 sin 30 t
i = 20 sin ( 307-
In one cycle of alternate current, the average power
consumed by the circuit and the wattles current are,
respectively
(a) 50,0
(b) 50, 10
50
(d) 7,0
1000
v2.10
(JEE Main 2018)
12
14 Assertion
The quantity ( L / R ) possesses dimension of time
Reason
To reduce the rate of increase of current
through a solenoid, we should increase the time constant ( (boldsymbol{L} / boldsymbol{R}) )
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
15 A charged ( 30 mu mathrm{F} ) capacitor is connected to a ( 27 mathrm{mH} ) inductor. The
angular frequency of free oscillations of the circuit is
A ( cdot 1.1 times 10^{3} r a d s^{-1} )
B. ( 2.1 times 10^{3} r a d s^{-1} )
c. ( 3.1 times 10^{3} r a d s^{-1} )
D. ( 4.1 times 10^{3} r a d s^{-1} )
12
16 A resistance ( boldsymbol{R} ) and a capacitor ( boldsymbol{C} ) are
joined to a source of ( boldsymbol{A} boldsymbol{C} ) of constant
e.m.f and variable frequency.
The potential difference across ( C ) is ( V )
If the frequency of ( boldsymbol{A} boldsymbol{C} ) is gradually increased, ( boldsymbol{V} ) will
A. increase
B. decrease
c. remain constant
D. first increase and then decreas
12
17 A step-up transformer operates on a ( 230 mathrm{V} ) line and supplies aload of 2 amp. The ratio of the primary and secondary windings is ( 1: 25 . ) The current in the primary is
( A cdot 15 A )
B. 12.5 A
( c cdot 25 A )
D. 50 A
12
18 ( mathbf{A} )
( mathbf{5 0 0} Omega ) resistor and a capacitor ( C ) are
connected in series across ( 50 H z . A C )
supply mains. The r.m.s potential
difference recorded on voltmeter ( V_{1} ) and
( V_{2} ) are ( V_{1}=120 V ) and ( V_{2}=160 mathrm{V} . ) The
power taken from the mains is:
4. ( 480 mathrm{W} )
В. 240 И
c. ( 28.8 W )
D. ( 14.4 mathrm{W} )
12
19 Distinguish between step-up and step
down transformer.
12
20 The unit of susceptance is
( A cdot ) ohm
B. ohm ( ^{-1} )
c. ohm/cm
D. ohm/m
12
21 The average power dissipation in pure inductance in AC circuit, is
A ( cdot 1 / 2 L i^{2} )
B . ( 2 L i^{2} )
c. ( L i^{2} / 4 )
D. zero
12
22 What is the main differences between a
step-up transformer and a step-down transformer?
12
23 Assertion: A capacitor blocks direct current in the steady state.

Reason : The capacitive reactance of the capacitor is inversely proportional to frequency f of the source of emf
A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
B. If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion.
c. If Assertion is true statement but Reason is false
D. If both Assertion and Reason are false statements

12
24 A sinusoidal voltage ( V=200 sin 314 t ) is
applied to a ( 10 Omega ) resistor. Find power dissipated as heat.
( mathbf{A} .500 W )
в. ( 1000 mathrm{W} )
c. ( 2000 W )
D. 3000W
12
25 A transmitter transmits at a wavelength
of ( 300 mathrm{m} . ) A condenser of capacitance ( 2.4 mu F ) is being used. The value of the
inductance for the resonant circuit is
approximately
B. ( 10^{-6} ) Н ( z )
( c cdot 10^{-8} mathrm{Hz} )
D. ( 10^{-10} ) Н ( z )
12
26 ( ln ) an oscillating ( L-C ) circuit in which
( C=4.00 mu F, ) the maximum potential
across the capacitor during the oscillations is ( 1.50 V ) and the maximum
current through the inductor is ( 50.0 m A )
What is the frequency of the oscillations?
12
27 The frequancy of oscillation of current in the inductor is-
A ( cdot frac{1}{3 sqrt{L C}} )
B. ( frac{1}{6 pi sqrt{L C}} )
c. ( frac{1}{sqrt{L C}} )
D. ( frac{1}{2 pi sqrt{L C}} )
12
28 A resonant A.C. circuit contains a
capacitor of capacitance ( 10^{-6} mathrm{F} ) and an inductor of ( 10^{-4} ) H. The frequency of oscillations will be :
( mathbf{A} cdot 10^{5} ) Нz
в. 10 Н ( z )
( ^{mathrm{c}} cdot frac{10^{5}}{2 pi} mathrm{Hz} )
D. ( frac{10}{2 pi} ) нг
12
29 Compute the energy stored in the
capacitor at ( t=2.00 m s )
A. ( 9.5531 mu J )
B. ( 6.5531 mu J )
c. ( 3.5531 mu J )
D. ( 2.5531 mu J )
12
30 At low frequency a condenser offers:
A. high impedance
B. low impedance
C. zero impedance
D. impedance of condenser is independent of frequency
12
31 A circuit consists of a resistor,an
inductor and a capacitor connected in series. If the resistance of a resistor is
( 25 Omega ) and the value of inductive
reactance is equal to capacitive
reactance, then the net impedance of the circuit will be :
A . ( 5 Omega )
B. 25Omega
c. ( 125 Omega )
D. ( 625 Omega )
12
32 If an alternating current ( boldsymbol{i}=boldsymbol{i}_{m} sin omega boldsymbol{t} ) is
flowing through a capacitor then
voltage drop ( Delta V_{C} ) across capacitor ( C )
will be?
A ( cdot-frac{i_{m}}{omega C} sin omega t )
в. ( -frac{i_{m}}{omega C} cos omega t )
c. ( -frac{i_{m}}{omega C}left(sin omega t+frac{pi}{4}right) )
D. ( frac{i_{m}}{omega C}left(sin omega t-frac{pi}{4}right) )
12
33 ( ln ) a series ( L-C-R ) circuit, current in
the circuit is ( 11 A ) when the applied voltage is ( 220 V . ) Voltage across the
capacitor is ( 200 V . ) If value of resistor
( 20 Omega, ) then the voltage across the unknown inductor is
A. zero
в. ( 200 mathrm{V} )
( c .20 V )
D. None of these
12
34 In a transformer the transformation
ratio is ( 0.3 . ) If ( 220 mathrm{V} ) ac is fed to the
primary, then the voltage across the secondary will be
A . ( 44 mathrm{V} )
B. 55
( c cdot 60 v )
D. 66 V
12
35 ( ln ) an ( A C ) circuit ( V ) and ( I ) are given by
( boldsymbol{V}=mathbf{1 0 0} sin (mathbf{1 0 0} boldsymbol{t}) ) volt, ( boldsymbol{I}= )
( 100 sin left(100 t+frac{pi}{3}right) ) amp the power
dissipated in the circuit is
A . ( 5.0 k W )
в. ( 2.5 k W )
c. ( 1.25 k W )
D. zero
12
36 The rms value of current in an ( A C )
circuit is ( 10 A . ) What is the peak
current?
A . ( 14.1 A )
B. ( 35.2 A )
( mathrm{c} .58 .9 A )
D. ( 23.5 A )
12
37 How many primary volts must be applied to a transformer with a
secondary to primary turns ratio of 0.1
to obtain a secondary voltage of ( 9 V ? )
A . ( 9 V )
B. ( 90 V )
( mathbf{c} .900 V )
D. ( 0.9 V )
12
38 A broadcasting centre broadcasts at 300 metre band. A capacitor of capacitance ( 2.5 mu mathrm{F} ) is available. The value of the inductance required for resonant circuit is nearly
A ( cdot 1 times 10^{-4} mathrm{H} )
В. ( 1 times 10^{-8} mathrm{H} )
c. ( 1 times 10^{-6} H )
D. ( 1 times 10^{-2} H )
12
39 A step up transformer converts ( 100 mathrm{V} ) at
primary to ( 300 mathrm{V} ) at secondary. If the primary current is ( 6 A ), then the secondary current is ( A )
A . 4
B. 8
c. 2
D. 10
12
40 (c) 200 S2 and 1.UH
T
27. In the circuit shown in the figure, R is a pure resistor
an inductor of negligible resistance (as compared to R)
is a 100 V, 50 Hz ac source of negligible resistance. With
either key K, alone or K, alone closed, the current is I.
If the source is changed to 100 V, 100 Hz the current with
K alone closed and with K, alone closed will be, respec
tively,
KIA K2
As
(b) 10, 21,
(C) 21., 70
(d) 210,0
WW
12
41 () 0.UA
30. In a series LCR circuit, the voltage across the resistance,
capacitance and inductance is 10 V each. If the capacitance
is short circuited, the voltage across the inductance will be
(a) 10 V
(b) 10/2 V
(c) (10/3)V
(d) 20 V
12
42 The values of ( X_{L}, X_{C} ) and ( R ) in series
with an A.C. circuit are ( 8 Omega, 6 Omega ) and ( 10 Omega )
respectively. The total impedance of the circuit will be
( Omega )
A . 10.2
B. 12.2
c. 10
D. 24.4
12
43 50. The power factor of the circuit in the figure is 1/2
The capacitance of the circuit is equal to
2 sin(1001)
10 S2
w
0.1 H
mm
(a) 400 uF
(c) 500 uF
(b) 300 uF
(d) 200 uF
12
44 ( ln L C R operatorname{series} A C ) circuit
A. If ( R ) is increased current will decrease
B. If ( L ) is increased current will decrease
c. If ( C ) is increased current will increase.
D. If ( C ) is increased current will decrease.
12
45 The peak voltage of an AC supply is
( 300 V . ) What is the rms voltage?
A ( .121 .2 V )
( V )
B. 212.1V
c. ( 343.4 V )
D. ( 434.3 V )
12
46 Current of ( frac{50}{pi} H z ) frequency is passing through an A.C circuit having series combination of resistance ( boldsymbol{R}=mathbf{1 0 0} mathbf{Omega} )
and inductor ( L=1 H, ) then phase
difference between voltage and current
is
A ( cdot 60^{circ} )
B. ( 30^{circ} )
( c cdot 45^{circ} )
D. ( 90^{circ} )
12
47 8. In an LCR circuit capacitance is changed from C to
For the resonant frequency to remain unchanged. th
inductance should be change from L to
(a) 4L
(b) 2L
(c) L/2
(d) L/4
(AIEEE 2004
12
48 ( ln L_{-} C ) oscillation, maximum charge on
capacitor is ( Q_{0} . ) The current in the
circuit, when ( 50 % ) energy is electrical
and ( 50 % ) is magnetic is
A ( cdot frac{Q_{0}}{sqrt{L C}} )
B. ( frac{Q_{0}^{2}}{sqrt{L C}} )
с. ( frac{Q_{0}}{2 sqrt{L C}} )
D. ( frac{Q_{0}}{sqrt{2 L C}} )
12
49 At inductance ( 1 H ) is connected in
series with an ( A C ) source of ( 220 mathrm{V} ) and
( mathbf{5 0} boldsymbol{H} z . ) The inductive resistance (in
ohm) is :
A ( .2 pi )
в. ( 50 pi )
( c .100 pi )
D. ( 1000 pi )
12
50 A resistor of resistance ( 100 Omega ) is
connected to an AC source ( epsilon= )
( (12 V) sin left(250 pi s^{-1}right) t )
Find the power consumed by the bulb.
12
51 Express ( q ) as a function of time.
A ( cdot 10^{4} cos left(6.28 times 10^{3} tright) )
B ( cdot 10^{-4} cos left(9.28 times 10^{3} tright) )
( mathbf{c} cdot 10^{-4} cos left(6.28 times 10^{3} tright) )
D ( cdot 10^{-4} cos left(6.28 times 10^{-3} tright) )
12
52 An inductor ( 2 / pi mathrm{F} ) and a resistor ( 100 / pi )
are connected in series across a source
of emf ( mathbf{v}=mathbf{1 0} sin 100[pi mathrm{t}] . ) Here ( mathrm{t} ) is in
second.
(a) find the impedance of the circuit find the energy dissipated in the circuit in 20 minutes.
12
53 In an L.C.R series a.c circuit, the current,
the current
A. is always in phase with the voltage
B. always lags the generator voltage
C . always leads the generator voltage
D. None of these
12
54 The instantaneous value of emf and
current in an A.C. circuit are; ( boldsymbol{E}= )
( 1.414 sin left(100 pi t-frac{pi}{4}right), I= )
( 0.707 sin (100 pi t) . ) The admittance of
the circuit will be mho.
A ( cdot frac{1}{sqrt{2}} )
B. ( sqrt{2} )
( c cdot frac{1}{2} )
D.
12
55 In the secondary coil of a step up transformer, the number of turns of the copper wire are :
A. More and the wire is thick
B. More and the wire is thin
c. Less and the wire is thick
D. Less and the wire is thin
12
56 When an a.c. source of e.m.f. ( boldsymbol{E}= )
( E_{0} sin 100 t ) is connected across a
circuit, it is observed that voltage leads the current by a phase angle ( frac{pi}{4} . ) If the circuit consists possible only R-L, R-C or L-C in series the two elements could be.
B. ( R=10 Omega, C=1000 mu F )
c. ( R=100 Omega, C=1000 mu F )
D. ( R=10 Omega, L=100 m H )
12
57 Statement A: With an increase in the
frequency of AC supply inductive reactance increases.
Statement B: With an increase in the
frequency of AC supply capacitive reactance increase.
A. A is true but B is false
B. Both A and B are true
c. A is false but B is true
D. Both A and B are false
12
58 A resistance ( (boldsymbol{R})=12 Omega ; ) inductance
( (L)=2 ) henry and capacitive reactance ( C=5 m F ) are connected in series to an
ac generator, then:
A. at resonance, the circuit impedance is zero
B. at resonance, the circuit impedance is ( 12 Omega )
c. the resonance frequency of the circuit is ( 1 / 2 pi )
D. at resonance, the inductive reactance is less than the capacitive reactance
12
59 A device that increases the voltage of
an alternating current is called a(n)
A. Electric motor
B. Galvanometer
c. step-up transformer
D. step-down transformer
12
60 A choke is preferred to a resistance for limiting current in AC circuit because:
A. Choke is cheap
B. There is no wastage of power
c. choke is compact in size
D. Choke is a good absorber of heat
12
61 Keeping the source frequency equal to
the resonating frequency of the series
LCR circuit, if the three elements, ( L, C )
and ( R ) are arranged in parallel, show that the total current in the parallel LCR
circuit is minimum at this frequency.
Obtain the current RMS value in
each branch of the circuit for the
elements and source specified as below
for this frequency.
The figure shows a series LCR circuit
connected to a variable frequency ( 230 V )
source. ( boldsymbol{L}=mathbf{5 . 0 H}, boldsymbol{C}=mathbf{8 0} boldsymbol{mu} boldsymbol{F}, boldsymbol{R}= )
( 40 Omega )
12
62 An LC circuit contains a ( 20 mathrm{mH} )
inductor and a ( 25 mu ) F capacitor with an initial charge of 5 mC. The total energy stored in the circuit initially is
A . 5 J
в. 0.5
c. 50
D. 500 J
12
63 The current flowing through the resistor
in a series LCR a.c. circuit, is ( boldsymbol{I}=varepsilon / boldsymbol{R} )
Now the inductor and capacitor are
connected in parallel and joined in series with the resistor as shown in
figure. The current in the circuit is now.
(Symbols have their usual meaning)
A . equal to I
B. more than I
c. less than 1
D. zero
12
64 A sinusoidal voltage ( V=200 sin 314 t )
is applied to a ( 10 Omega ) resistor. Find rms
voltage.
A . ( 141.4 V )
B. ( 314.2 V )
c. ( 519.6 V )
D. 278.9V
12
65 When the current in the inductor has
half its maximum value, what is the charge on the capacitor?
A ( cdot 1.33 times 10^{6} C )
B. ( 9.33 times 10^{-6} C )
( mathbf{c} cdot 4.33 times 10^{-6} C )
D. ( 7.33 times 10^{6} C )
12
66 1. When 100 volts dc is supplied across a solenoid, a current
of 1.0 ampere flows in it. When 100 volt ac is applied
across the same coil, the current drops to 0.5 ampere. If
the frequency of ac source is 50 Hz, then the impedance
and inductance of the solenoid are
(a) 200 2 and 0.55 henry
(b) 100 2 and 0.86 henry
(c) 200 S2 and 1.0 henry
(d) 100 2 and 0.93 henry
12
67 What is the inductance of the inductor?
A ( .9 .31 mu H )
в. о.931цн.931ин
D. ( 93.1 mu H )
12
68 The number of turns in the primary coil
of a transformer is 200 and the number
turns in the secondary coil is 10 If 240 volt a.c is applied to the primary the output from seconsry will be:
A . 48 v
B. 24
c. ( 12 mathrm{v} )
( D cdot 6 v )
12
69 An ac voltage is applied to a resistance ( mathrm{R} ) and an inductor ( mathrm{L} ) in series. If ( mathrm{R} ) and
the inductive reactance are both equal
to ( 3 Omega, ) the phase difference between the
applied voltage and the current in the circuit is:
A. zero
в.
( c cdot frac{pi}{4} )
D. ( frac{pi}{2} )
12
70 A ( 300 Omega ) resistor is connected in series
with a ( 0.800 H ) inductor. The voltage
across the resistor as a function of time
is ( V_{R}=(2.50 V) cos [(950 r a d / s) t] )
Determine the inductive reactance of
the inductor.
12
71 In an a.c. circuit ( mathrm{V} ) and I are given by ( V=50 sin 50 t ) volt and ( I= )
( 100 sin (50 t+pi / 3) mathrm{mA} . ) The power
dissipated in the circuit
A. 2.5 kw
B. 1.25 kw
c. ( 5.0 mathrm{kw} )
D. 500 watt
12
72 In the circuit shown below, the key Kis
closed at ( t=0 . ) The current through the battery is:
A. ( frac{mathrm{VR}_{1} mathrm{R}_{2}}{sqrt{mathrm{R}_{1}^{2}+mathrm{R}_{2}^{2}}} ) at ( mathrm{t}=0 ) and ( frac{mathrm{V}}{mathrm{R}_{2}} ) at ( mathrm{t}=infty )
( frac{V}{R_{2}} a t t=0 ) and ( frac{Vleft(R_{1}+R_{2}right)}{R_{1} R_{2}} ) at ( t=alpha )
C ( cdot frac{mathrm{V}}{mathrm{R}_{2}} mathrm{att}=0 ) and ( frac{mathrm{VR}_{1} mathrm{R}_{2}}{sqrt{mathrm{R}_{1}^{2}+mathrm{R}_{2}^{2}}} ) at ( mathrm{t}=infty )
( frac{Vleft(R_{1}+R_{2}right)}{R_{1} R_{2}} a t t=0 ) and ( frac{V}{R_{2}} ) at ( t=infty )
12
73 In an a.c. circuit the voltage applied is ( boldsymbol{E}=boldsymbol{E}_{0} sin omega boldsymbol{t} . ) The resulting current in
the circuit is ( boldsymbol{I}=boldsymbol{I}_{0} sin left(boldsymbol{omega} boldsymbol{t}-frac{boldsymbol{pi}}{2}right) . ) The
power consumption in the circuit is given by –
A ( cdot quad P=frac{E_{0} I_{0}}{sqrt{2}} )
B . ( P= ) zero
c. ( _{P}=frac{E_{0} I_{0}}{2} )
D. ( P=sqrt{2} E_{0} I_{0} )
12
74 An LCR series circuit is
under resonance. If ( I_{m} ), is current
amplitude, ( V_{m} ) is voltage amplitude, ( R ) is the resistance, ( Z ) is the impedance,
( X_{L} ) is the inductive reactance and ( X_{C} )
is the capacitive reactance, then
( ^{mathrm{A}} cdot_{I_{m}}=frac{Z}{V_{m}} )
в. ( _{I_{m}}=frac{V_{m}}{X_{L}} )
( mathbf{c} cdot_{I_{m}}=frac{V_{m}}{X_{C}} )
D. ( _{I_{m}}=frac{V_{m}}{R} )
12
75 43. Power factor is one for
(a) pure resistor
(b) pure inductor
(c) pure capacitor
(d) either an inductor or a capacitor
12
76 The primary and secondary coil of a transformer have 50 and 1500 turns
respectively. If the magnetic flux ( phi ) linked with primary coil is given by
( phi=phi_{0}+4 t, ) where is in webers, ( t ) is
time in seconds and ( phi ) is a constant, the
output voltage across the secondary coil is:
( A cdot 150 V )
B. 90
c. ( 120 v )
D. ( 180 mathrm{V} )
12
77 In the circuit of given figure (1) and (2) are ammeters. Just after key ( boldsymbol{K} ) is pressed to complete the circuit, the reading is
A. maximum in both 1 and 2
B. zero in both 1 and 2
c. zero in 1 , minimum in 2
D. maximum in 1, zero in 2
12
78 A series ( L C R ) circuit containing a
resistance of ( 120 Omega ) has angular
resonance frequency ( 4 times 10^{5} ) rad ( s^{-1} )
At resonance the voltages across
resistance and inductance are ( 60 V )
and ( 40 mathrm{V} ), respectively. The value of
inductance ( L ) is
A. ( 0.1 mathrm{mH} )
в. ( 0.2 mathrm{mH} )
c. ( 0.35 mathrm{mH} )
D. ( 0.4 mathrm{mH} )
12
79 What is the average power dissipation in an ideal capacitor in AC circuit?
( mathbf{A} cdot 2 C V^{2} )
в. ( frac{1}{2} C V^{2} )
c. ( Z ) ero
D. ( C V^{2} )
12
80 A LC-circuit contains a ( 20 m H ) inductor
and a ( 50 mu F ) capacitor with an initial
charge of ( 10 m C . ) The resistance of the
circuit is negligible. Let the instant the
circuit is closed be ( t=0 )
(a) What is the total energy stored initially. Is it conserved during the LCoscillations?
(b) What is the natural frequency of the circuit?
(c) At what times is the energy stored?
(i) completely electrical (ie., stored in the capacitor)?
(ii) completely magnetic (i.e., stored in the inductor)?
(d) At what time is the total energy shared equally between the inductor and the capacitor
12
81 ( ln ) an ( A C ) circuit, the potential across an inductance and resistance joined in series are respectively ( 16 V ) and ( 20 V )
The total potential difference across the circuit is
( mathbf{A} cdot 20.0 V )
B . ( 25.6 V )
c. ( 31.9 V )
D. 33.6 ( V )
12
82 the values of ( I, C ) and ( R ) for a circuit are 1
( mathrm{H}, 9 mathrm{F}, ) and ( 3 Omega ). what is the quality factor for the circuit at resonance?
( A )
B. 9
( c cdot 19 )
D. 13
12
83 The ratio of primary voltage to secondary voltage in a transformer is
‘n’. The ratio of the primary current to secondary current in the transformer is
( A )
B. ( 1 / n )
c. ( n^{2} )
D. ( 1 / n^{2} )
12
84 The inductor in a ( L-C ) oscillation has
a maximum potential difference of ( 16 V ) across the inductor of ( 3 m H ) and
maximum energy of ( 160 mu J . ) The value
of capacitor in ( L-C ) circuit is :
( mathbf{A} cdot 0.8 mu F )
B. ( 0.625 mu F )
c. ( 1.6 mu F )
D. ( 1.25 mu F )
12
85 12. In an AC generator, a coil with N turns, all of the same
area A and total resistance R, rotates with frequency o
in a magnetic field B. The maximum value of the emf
generated in the coil is.
(a) N.A.B.R.
(b) N.A.B. O
(c) N.A.B.R. O (d) N.A.B (AIEEE 2006)
12
86 ( ln ) an ( A . C . ) circuit a capacitor of ( 1 mu F )
value is connected to a source of
frequency 1000 rad/sec. The value of capacitive reactance will be
A . ( 10 Omega )
в. 100Omega
c. ( 1000 Omega )
D. ( 10,000 Omega )
12
87 n the circuit shown in figure, the ( A C )
source gives a voltage ( V= )
( 20 cos (2000 t) . ) Neglecting source
resistance, the voltmeter and ammeter
readings will be
A. ( 0 V .2 .0 )
В. ( 0 V, 1.4 A )
( c .5 .6 V, 1.4 )
) ( .8 V, 2.0 A )
12
88 The diagram below in Fig. shows the core of a transformer and its input and
output connections.
The name of the transformer is
(step-up, stepdown) transformer.
12
89 12. An ac voltage is represented by E = 220 V2 cos(501)
How many times will the current become zero in 1 s?
(a) 50 times
(b) 100 times
(C) 30 times
(d) 25 times
12
90 A circuit containing a ( 20 Omega ) resistor and
0.1 ( mu F ) capacitor in series is connected to 230 V AC supply of angular frequency 100 rad ( s^{-1} . ) The impedance of the circuit is
A ( cdot 10^{5} Omega )
B . ( 10^{4} Omega )
( mathbf{c} cdot 10^{6} Omega )
D. ( 10^{10} Omega )
12
91 If the bandwidth of a filter increases:
A. Q factor decreases
B. the roll-off rate increases
c. the half-power frequency decreases
D. the center frequency decreases
12
92 An inductive coil has a resistance of
100 ( Omega ). When an a.c. signal of frequency ( 1000 H z ) is fed to the coil, the applied
voltage leads the current by ( 45^{circ} . ) What
is the inductance of the coil?
( mathbf{A} cdot 10 m H )
в. ( 12 m H )
c. ( 16 m H )
D. ( 20 m H )
12
93 In the method using the transformers,
assume that the ratio of the number of
turns in the primary to that in the secondary in the step-up transformer is ( 1: 10 . ) If the power to the consumers has to be supplied at ( 200 mathrm{V} ), the ratio of the number of turns in the primary to that in the secondary in the step-down transformer is
( A cdot 200: 1 )
B. 150:1
c. 100: 1
D. 50:
12
94 The alternating emf applied and the current flowing in an ( A C ) circuit are
represented by ( boldsymbol{E}=boldsymbol{E}_{0} sin omega boldsymbol{t} ) and
( I_{0} sin left(omega t+frac{pi}{2}right) ) respectively. The power
loss in the circuit will be
A . zero
в. ( frac{E_{0} I_{0}}{2} )
c. ( frac{E_{0} I_{0}}{sqrt{2}} )
D. ( frac{E_{0} I_{0}}{4} )
12
95 toppr ( = )
Q Type your question.
( B )
( c )
( D )
12
96 The maximum charge on the capacitor is given as ( (text { in } n C) ) 12
97 13. In the circuit shown below, the ac source has voltage V=
20cos(ot) volts with o= 2000 rad/sec. The amplitude of
the current will be nearest to
692
50
F
5 mH, 422
mm
(b) 3.3 A
(a) 2 A
(c) 2115 A
(d) V5 A
12
98 In a series L-C circuit, if ( L=10^{-3} mathrm{H} ) and
( C=3 times 10^{-7} F ) is connected to a
( 100 V-50 H z ) a.c. source, the
impedance of the circuit is
A ( cdot frac{10^{5}}{3 pi}-10 pi )
В. ( 0.1 pi-3 times 10^{-5} pi )
( ^{mathbf{C}} cdot frac{10^{5}}{3 pi}-frac{pi}{10} )
D. None of these
12
99 If the values of ( L, C ) and ( R ) in a series
( boldsymbol{L}-boldsymbol{C}-boldsymbol{R} ) circuit are ( 10 mathrm{mH}, 100 mu boldsymbol{F} )
and ( 100 Omega ) respectively then the value of resonant frequency will be
( ^{mathbf{A}} cdot frac{10^{3}}{2 pi} H z )
в. ( 2 times 10^{3} H z )
c. ( _{2 times frac{10^{3}}{p i}} H z )
D. ( 10^{3} H z )
12
100 The value of alternating emf in the following circuit will be
A. 220 volt
B. 140 volt
c. 20 volt
D. 100 volt
12
101 A transformer has 500 turns of the
primary winding and 10 turns of the secondary winding. Determine the secondary voltage if the secondary circuit is open and the primary voltage is ( 120 mathrm{V} )
12
102 Define quality factor. 12
103 The primary of a transformer has 40
turns and works on 100 volt and 100
watt. Then the number of turns in the
secondary to step up voltage to ( 400 mathrm{V} ) and the current in the secondary and primary will be
A. ( 260,0.25 mathrm{A}, 2 mathrm{A} )
B. 160, 0.25A, 1A
c. ( 360,0.55 mathrm{A}, ) 1А
D. None of these
12
104 The current in LCR circuit is maximum
when :
A ( . X_{L}=0 )
В . ( X_{L}=X_{C} )
c. ( X_{C}=0 )
D. ( X_{L}^{2}+X_{C}^{2}=1 )
12
105 A circuit consists of a coil with
inductance ( L ) and an uncharged capacitor of capacitance C.The coil is in a constant uniform magnetic field such
that the flux through the coil is ( mathbf{Phi} . mathbf{A t} )
time ( t=0, ) the magnetic field is
abruptly switched off. Let ( omega_{0}=1 / sqrt{L C} )
and ignore the resistance of the circuit.
Then:
A . current in the circuit is ( I(t)=(Phi / L) cos omega_{0} t )
B. Magnitude of the charge on the capacitor is ( |Q(t)|= ) ( 2 C omega_{0} mid sin omega_{0} t )
C. initial current in the circuit is infinite
D. initial charge on the capacitor is ( C omega_{0} Phi )
12
106 What do we name the device which
increases the emf?
A. electric generator
B. step-up transformer
c. electric motor
D. none of these
12
107 Joule’s Law for heat produced is valid for
A . Resistance
B. Inductance
c. capacitance
D. Battery
12
108 51. In an LR circuit connected to a battery, the rate at whin
energy is stored in the inductor is plotted against time
during the growth of current in the circuit. Which of the
following best represents the resulting curve?
Rate
Rate
(a)
(b)
Time
→ Time
Rate
Rate
(d)
Time

Time
min lenodot
12
109 A transformer converts ( 200 V ) a.c. to
( mathbf{5 0} boldsymbol{V} ) a.c.The secondary has ( mathbf{5 0} ) turns
and load across it draws ( 300 m A )
current.Calculate the current in the
primary:
12
110 A certain step-up transformer has 400 turns in the primary winding and 2,000 turns in the secondary winding. The turns ratio is
A . 0.2
B. 0.4
( c .5 )
D. 25
12
111 The inductance of a resistanceless coil
is 0.5 henry. In the coil, the value of alternating current is ( 0.2 mathrm{A} ) whose frequency is 50 Hz. The reactance of circuit is
( A cdot 15.7 Omega )
в. ( 157 Omega )
c. ( 1.57 Omega )
D. 757Omega
12
112 A pure capacitor is connected in an ( A C ) circuit.The power factor of the circuit will be
( A )
B. infinity
c. zero
D. 0.5
12
113 If a transformer have turn ratio 5
frequency ( 50 H z ) root mean square value of potential difference on primary
100 volts and the resistance of the
secondary winding is ( 500 Omega ) then the peak value of voltage in secondary winding will be (the efficiency of the transformer is hundred percent)
A. ( 500 sqrt{2} )
2
в. ( 10 sqrt{2} )
c. ( 50 sqrt{2} )
2
D. ( 20 sqrt{2} )
12
114 ‘Z’ is not.
A. Atomic number
B. Impedance
C. Zeta potential
D. Partition function
12
115 Four different circuit components are
given in each situation of List 1 and al the components are connected across
an ac source of same angular frequency ( omega=200 mathrm{rad} s^{-1} . ) The information of
phase difference between the current
source voltage in each situation of List 1 is given in List ( 2 . ) Match the circuit components in List 1 with the corresponding List 2
12
116 ( frac{k}{k} ) 12
117 In the figure shown, ( q ) is in coulomb and ( t ) in second. At time ( t=1 s )
This question has multiple correct options
A ( cdot V_{a}-V_{b}=4 V )
в. ( V_{b}-V_{c}-1 V )
C ( . V_{c}-V_{d}=16 V )
D. ( V_{a}-V_{d}=20 V )
12
118 If the reading in voltmeter ( V_{1} ) is ( 40 V )
then what is the reading of voltmeter ( V_{2} )
12
119 What is the value of inductance ( L ) for
which the current flowing is maximum in a series LCR circuit with ( C=10 mu F )
and ( omega=1000 s^{-1} ? )
A. ( 100 m H )
в. ( 1 m H )
c. Cannot be calculated unless ( R ) is known
D. ( 10 m H )
12
120 The transformer voltage induced in the secondary coil of a transformer is mainly due to:
A. a varying electric field
B. a varying magnetic field
c. the vibrations of the primary coil
D. the iron core of the transformer
12
121 The given graph(a) and (b) represent the variation of the opposition offered by the circuit element to the flow of
alternating current, with frequency of the applied emf. Identify the circuit element corresponding to each graph.
12
122 n the circuit shown in figure, the ( A C )
source gives a voltage ( V= )
( 20 cos (2000 t) . ) Neglecting source
resistance, the voltmeter and ammeter
readings will be
A. ( 0 V .2 .0 )
В. ( 0 V, 1.4 A )
( c .5 .6 V, 1.4 )
) ( .8 V, 2.0 A )
12
123 A capacitor acts as an infinite resistance for
A . ( D C )
B. ( A C )
c. ( D C ) as well as ( A C )
D. neither ( A C ) nor ( D C )
12
124 An ( L-C-R ) series circuit with ( L= )
( mathbf{0 . 1 2 0 H}, boldsymbol{R}=mathbf{2 4 0 Omega}, ) and ( boldsymbol{C}=mathbf{7 . 3 0 mu} boldsymbol{F} )
carries an rms current of ( 0.450 A ) with a
frequency of ( 400 H z . ) What is the impedance of the circuit?
12
125 For a transformer, the turns ratio is 3 and its efficiency is ( 0.75 . ) The current flowing in the primary coil is ( 2 A ) and the
voltage applied to it is ( 100 mathrm{V} ). Then the
voltage and the current flowing in the secondary coil are
respectively.
A. ( 150 V, 1.5 A )
B . ( 300 V, 0.5 A )
c. ( 300 V, 1.5 A )
D. ( 150 V, 0.5 A )
12
126 An ideal inductor is in turn put across
( 220 V, 50 H z ) and ( 220 V, 100 H z )
supplies. The current flowing through it in the two cases will be then
A. equal
B. different
c. zero
D. infinite
12
127 The number of turns in the primary and
the secondary coils of a transformer are
1000 and 3000 respectively. If the primary of the coil is connected to 80
volt ac, then what is the potential difference per turn of the secondary coil
( ? )
A . 240
B. 24
c. ( 0.24 v )
D. 0.08 ( v )
12
128 can be moved from ( a ) to ( b, ) connecting
either inductance ( L ) or capacitance ( C )
to a resistor ( R ) when the key is pressed
the switch ( S ) will be at either ( a ) or ( b ). In
column ( I, ) the variation of physical
quantities charge,current,voltage etc.in
time are given in terms of constants
( C^{prime} s ) and ( K^{prime} s ) the values of which
depends on emf ( V, R, L ) and ( C . ln )
column ( boldsymbol{I} boldsymbol{I}, ) the physical quantities
under different switch positions are
given. the variation in column ( boldsymbol{I} ) may
correspond to one or more quantities of
Column ( boldsymbol{I} boldsymbol{I} )
12
129 Average power consumed by the circuit 12
130 A transformer having the efficiency of ( 90 % ) is working on ( 200 V ) and ( 3 k W ) power supply. If the current in the secondary coil is ( 6 A ), the voltage across the secondary coil and the
current in the primary coil respectively are:
A. ( 300 V, 15 A )
в. ( 450 V, 15 A )
c. ( 450 V, 13.5 A )
D. ( 600 V, 15 A )
12
131 Define quality factor of resonance in
series LCR circuit. What is its Sl unit?
12
132 A transformer steps up an ac supply from 220 to 2200 V. If the secondary coi of the transformer has 2000 turns, Then
find the number of turns in its primary coil.
12
133 An ( A C ) voltage source of variable
angular frequency ( omega ) and fixed
amplitude ( V_{0} ) is connected in series
with a capacitance ( C ) and an electric bulb of resistance ( boldsymbol{R} ) (inductance zero)
When ( omega ) is increased
A. the bulb glows dimmer
B. the bulb glows brighter
C. total impedance of the circuit is unchanged
D. total impedance of the circuit increases
12
134 When a voltage ( V_{s}=200 sqrt{2} sin (omega t+ )
( left.15^{circ}right) V ) is applied to an ac circuit, the
current in the circuit is found to be ( i= )
( 2 sin [omega t+(pi / 4)] A . ) If the average power
consumed in the circuit is ( x sqrt{6} W ). Find
( boldsymbol{x} )
12
135 Prove for an a.c. circuit:
( boldsymbol{P}_{boldsymbol{a v}}=boldsymbol{V}_{boldsymbol{r m s}} times boldsymbol{I}_{boldsymbol{r m s}} times cos boldsymbol{phi} )
12
136 The power loss in an ( A C ) circuit is ( E_{r m s} )
( I_{r m s}, ) when in the circuit there is only
A. ( C )
в. ( L )
( c . R )
D. ( L, C ) and ( R )
12
137 An ( L C R ) series circuit with ( R=100 Omega )
is connected to a ( 200 mathrm{V}, 50 mathrm{Hz} ) a.c source. When only the capacitance is removed, the current leads the voltage
by ( 60^{circ} . ) When only the inductance is removed, the current leads the voltage
by ( 60^{circ} . ) The current in the circuit is :
A ( .2 A )
в. ( 1 A )
c. ( frac{sqrt{3}}{2} A )
D. ( frac{2}{sqrt{3}} A )
12
138 In a series resonant circuit, the AC voltage across resistance ( R, ) inductor and capacitor ( C ) are ( 5 vee, 10 vee ) and ( 10 ~ V ) respectively. The AC voltage applied to the circuit will be
A . ( 10 v )
B. 25
( c cdot 5 v )
D. 20
12
139 Which of the following statements is
true?

Heat produced in a current carrying conductor depends upon:
This question has multiple correct options
A. The time for which the current flows in the conductor
B. The resistance of the conductor
C. The strength of the current
D. The nature of current (ac or dc)

12
140 Voltage induced in the secondary coil of a transformer is mainly due to :
A. The iron core of the transformer
B. The vibrations of the primary coil
c. A varying induced electric field
D. A varying induced magnetic field
12
141 State whether given statement is True or False

The quality factor (Q) is the ratio of true
power to apparent power.
A. True
B. False

12
142 The average power dissipated in a pure inductor is
A ( cdot frac{1}{2} V I )
B. ( V I^{2} )
c. ( frac{V I^{2}}{4} )
D. zero
12
143 If the value of ( C ) in a series RLC circuit is
decreased, the resonant frequency
A. is not affected
B. increases
c. is reduced to zero
D. decreases
12
144 A coil has resistance 30 ohm and
inductive reactance 20 Ohm at ( 50 mathrm{Hz} ) frequency. If an ac source, of 200 volt, ( 100 mathrm{Hz}, ) is connected across the coil, the current in the coil will be :
( mathbf{A} cdot 4 cdot 0 mathrm{A} )
B. ( 8.0 mathrm{A} )
c. ( frac{20}{sqrt{13}} ) A
D. 2.0 A
12
145 Find the dimensions of ( frac{1}{sqrt{L C}}(L= ) Inductance, ( C=text { Capacitance }) )
( mathbf{A} cdot T^{-1} )
B. ( T^{-2} )
( c . T )
D. ( L )
12
146 In a step-up transformer, the number of turns in the primary are than the
number turns in the secondary.
A. more
B. less
c. same as
D. None of the above
12
147 If the resistance in parallel with a
parallel resonant circuit is reduced, the bandwidth
A. disappears
B. becomes sharper
c. increases
D. decreases
12
148 A ( 20 Omega ) resistor, ( 1.5 mathrm{H} ) inductor and ( 35 mu F )
capacitors are connected in series with
( 200 V, 50 H z ) ac supply. Calculate the
impedance of the circuit and also find the current through the circuit?
12
149 A transformer converts ( 200 mathrm{V} ) ac into
( 2000 mathrm{V} ) ac. Calculate the number of
turns in the secondary if the primary
has 10 turns.
12
150 A series RLC circuit is made as shown
in the figure with an ( A C ) source of ( 60 vee )
20 Hz. Then
This question has multiple correct options
A. the rms current through the resistor R is 4.2 A
B. the effective potential difference between P and should be ( 42 mathrm{v} )
c. the instantaneous current leads the source voltage by 45
D. the instantaneous current lags behind the applied voltage by ( 45^{circ} )
12
151 The current in resistance ( boldsymbol{R} ) at
resonance is
( A cdot ) zero
B. minimum but finite
c. maximum but finite
D. infinite
12
152 A condenser of capacity ( C ) is charged to a potential difference of ( V_{1} . ) The plates
of the condenser are then connected to
an ideal inductor of inductance L. The
current through the inductor when the potential difference across the
condenser reduces to ( V_{2} ) is:
A ( cdot frac{Cleft(V_{1}^{2}-V_{2}^{2}right)}{L} )
B. ( frac{Cleft(V_{1}^{2}+V_{2}^{2}right)}{L} )
c. ( sqrt{frac{Cleft(V_{1}^{2}-V_{2}^{2}right)}{L}} )
D. ( sqrt{frac{Cleft(V_{1}-V_{2}right)^{2}}{L}} )
12
153 What is the reactance in ohms of a
( 2.00 H ) inductor at a frequency of
( mathbf{5 0 . 0 H z} ? )
12
154 In a series combination of ( mathrm{R}, mathrm{L} ) and ( mathrm{C} ) to an
AC source at resonance, if ( mathrm{R}=20 Omega ), then impedance ( Z ) of the combination is
A . ( 20 Omega )
B. zero ( Omega )
( c cdot 1 Omega )
D. 400 ( Omega )
12
155 A capacitor has capacitance ( 0.5 n F . A )
choke of ( 5 mu H ) is connected in series. An
electromagnetic wave of wavelength ( lambda ) is found to resonate with it. Find ( lambda ) (in
meter)
( mathbf{A} cdot 10 pi )
в. ( 20 pi )
c. ( 30 pi )
D. ( 5 pi )
12
156 Above the resonant frequency,
A. the frequency of the body is less than the frequency of the external periodic force.
B. the frequency of the body is greater than the frequency of the external periodic force.
C. the frequency of the body is exactly equal to the frequency of the external periodic force.
D. both (A) and (B)
12
157 ( ln ) an ( A C ) circuit, voltage ( V=V_{0} sin omega t )
and inductor L is connected across the
circuit.Then the instantaneous power
will be
( ^{mathrm{A}} cdot frac{V_{0}^{2}}{2 omega L} sin omega t )
B. ( frac{-V_{-}^{2}}{2 omega L} ) sinwt
c. ( frac{-V_{0}^{2}}{2 omega L} sin 2 omega t )
D. ( frac{V_{0}^{2}}{omega L} sin 2 omega t )
12
158 The unit of ( sqrt{boldsymbol{L} boldsymbol{C}} ) is
A. Henry
B. Farad
c. second
D. Ampere
12
159 A protons is about 1840 times heavier
than an electron. When it is accelerated
by a potential difference of ( 1 k V ), its
kinetic will be:-
A. ( 1840 mathrm{keV} )
B . ( 1 / 1840 mathrm{keV} )
c. ( 1 mathrm{keV} )
D. ( 920 mathrm{keV} )
12
160 64. In the following electrical network at t < 0 (figure), key
is placed on (1) till the capacitor got fully charged. Key
is placed on (2) at t=0. Time when the energy in both the
capacitor and the inductor will be same for the first time
is
(1) (2)
(a) VLC
(b) 37 LC
(c) VLC
(1) 27 JIC
12
161 puudu
ideal choke takes a current of 10 A when connected
to an ac supply of 125 V and 50 Hz. A pure resistorm
the same conditions takes a current of 12.5 A. If the
are connected to an ac supply of 100 V and 40 Hz then
the current in series combination of above resistor and
inductor is
(a) 10/2 A
b) 12.5 A
(c) 20 A
(d) 10 A
12
162 (C) SU umes
(u) 25 Wes
13. The rms value of an ac of 50 Hz is 10 A. The time taken by
an alternating current in reaching from zero to maximum
value and the peak value will be
(a) 2 x 10-2s and 14.14 A
(b) 1 x 10-2 s and 7.07 A
(c) 5 x 10-3s and 7.07 A
(d) 5 x 10’s and 14.14 A
12
163 In the circuit shown, the switch ( S_{1} ) is
closed for long time and at ( t=0 ) s, the
switch ( S_{2} ) is closed and ( S_{1} ) is opened
simultaneously. What is the maximum charge (in the unit of ( mu C ) ) on the ( 4 mu F )
capacitor?
A ( cdot q_{0}=3 mu C )
В ( cdot q_{0}=6 mu C )
c. ( q_{0}=3.4 mu C )
D ( cdot q_{0}=6.8 mu C )
12
164 An inductance of ( 2 H ) carries a current
of ( 2 A . ) To prevent sparking when the circuit is broken a capacitor of ( 4 mu F ) is connected across the inductance. The
voltage rating of the capacitor is of the order of :
B. ( 10 V )
( mathbf{c} cdot 10^{5} V )
D. ( 10^{6} V )
12
165 Which of the following plots may
represent the reactance of a series ( L C )
combination?
( 4 cdot(a) )
( B .(b) )
( c cdot(c) )
( D cdot(d) )
12
166 The r.m.s. value of potential difference
shown in the figure is :
( A cdot V_{0} / sqrt{3} )
в. ( V_{0} )
( c cdot V_{0} / sqrt{2} )
D. ( V_{0} / 2 )
12
167 In A.C circuit having only capacitor, the current
A ‘ lags behind the voltage by ( frac{pi}{2} ) in phase
B. Ieads the voltage by ( frac{pi}{2} ) in phase
c. leads the voltage by ( pi ) in phase
D. lags behind the voltage by ( pi ) in phase
12
168 10
54. A simple LR circuit is connected to a battery at time
t = 0. The energy stored in the inductor reaches half its
maximum value at time

In
12
169 In a series LCR circuit connected to an
ac source of variable frequency and
voltage ( boldsymbol{v}=boldsymbol{v}_{m} sin omega boldsymbol{t}, ) draw a plot
showing the variation of current ( (boldsymbol{I}) )
with angular frequency ( (omega) ) for two
different values of resistance ( boldsymbol{R}_{1} ) and ( boldsymbol{R}_{2} )
( left(R_{1}>R_{2}right) . ) Write the condition under
which the phenomenon of resonance occurs. For which value of
the resistance out of the two curves a
sharper resonance is produced? Define Q-factor of the circuit and give its
significance.
12
170 62. In an LC circuit shown in figure, C = 1F, L=4 H. At time
t=0, charge in the capacitor is 4 C and it is decreasing at
the rate of 5 C s. Choose the correct statement.
(a) Maximum charge in the
capacitor can be 6 C
(b) Maximum charge in the
capacitor can be 8 C
(c) Charge in the capacitor
will be maximum after
time 3 sin (2/3) s
(d) None of these
will
12
171 The plot given below is of the average power delivered to an LRCLRC circuit
versus frequency. The quality factor of
the circuit is:
A . 5.0
B. 2.0
( c .2 .5 )
D. 0.4
12
172 In R-L-C series circuit, the potential differences across each element is ( 20 V )
Now the value of the resistance alone is
doubled, then P.D. across ( mathrm{R} ), L and ( mathrm{C} )
respectively.
A. ( 20 V, 10 V, 10 V )
В. ( 20 V, 20 V, 20 V )
c. ( 20 V, 40 V, 40 V )
D. ( 10 V, 20 V, 20 V )
12
173 In an oscillating ( L C ) circuit, the total
stores energy is ( U ) and the maximum
charge on the capacitor is ( Q . ) When the charge on the capacitor is ( Q / 2, ) the energy stored in the inductor is :
A. ( U / 2 )
в. ( U / 4 )
c. ( (4 / 3) U )
D. ( 3 U / 4 )
12
174 A ( 100 % ) efficiency transformer has 100
turns in the primary and 25 turm coil. If the current in the secondary coil is ( 4 A ) then the current in the primary coil is
( A cdot 1 A )
B. 4 A
( c cdot 8 A )
D. 16 A
12
175 In a series LCR circuit, the plot of ( boldsymbol{I}_{boldsymbol{m}} ) vs
( omega ) is shown in the figure. The bandwidth
of this plot will be then
A. Zero
B. ( 0.1 mathrm{rads}^{-1} )
c. ( 0.2 r a d s^{-1} )
D. ( 0.4 mathrm{rads}^{-1} )
12
176 Explain the term ‘sharpness of resonance’ in ac circuit. 12
177 59. In the circuit shown (figure), the cell is ideal. The coil has
an inductance of 4 H and zero resistance. F is a fuse of
zero resistance and will blow when the current through it
reaches 5 A. The switch is closed at t = 0. The fuse will
blow
(a) almost at once
(b) after 2 s
E=2V
(c) after 5 s
(d) after 10 s
12
178 A current source sends a current ( boldsymbol{I}- )
( i_{0} cos (omega t) . ) when connected across an
unknown load, it gives a voltage output
of ( boldsymbol{v}=boldsymbol{v}_{0} sin [boldsymbol{omega} boldsymbol{t}+(boldsymbol{pi} / mathbf{4})] ) across that
load. then the voltage across the current source may be brought in phase with the current through it by
A. Connecting an inductor in series with the load
B. Connecting a capacitor in series with the load
c. connecting an inductor in parallel with the loadd
D. connecting a capacitor in parallel with the load
12
179 In Fig, initially the capacitor is charged
to a potential of ( 5 mathrm{V} ) and then connected
to position across the inductor at
position 2. The maximum current
flowing in the LC circuit when the
capacitor is connected across the
inductor is :
( mathbf{A} cdot 10 A )
B. ( 20 A )
c. ( 30 A )
D. None of these
12
180 49. A coil has an inductance of 0.7 H and is joined in series
with a resistance of 220 2. When an alternating emf of
220 V at 50 cps is applied to it, then the wattless
component of the current in the circuit is (take 0.711=2.2]
(a) 5 A
(b) 0.5 A
(c) 0.7 A
(d) 7A
12
181 The voltage across ( boldsymbol{Q} ) is
7.60
( mathbf{A} cdot 20 V )
B. ( frac{sqrt{1350}}{10} V )
c. ( 5.5 V )
D. ( frac{sqrt{9524}}{10} V )
12
182 A varying current in the transformer’s
primary winding creates a varying
magnetic flux in the core and a varying
magnetic field impinging on the
A. iron core
B. electromagnetic field
C. secondary windings
D. none of the above
12
183 (u)
66. In the series circuit shown in the
figure the voltmeter reading will
be (all the meters are ideal):
(a) 300 V (b) 200 V
(c) 100 V (d) 600 V
12
184 The natural frequency of an LC – circuit
is 1,25,000 cycles per second. Then the capacitor ( C ) is replaced by another capacitor with a dielectric medium of dielectric constant k. In this case, the
frequency decreases by ( 25 k H z . ) The
value of k is:
A . 3.0
B. 2.
c. 1.56
D. 1.7
12
185 In a step up transformer, primary and secondary currents are ( 500 A ) and
( mathbf{1 0 0} A ). The ratio of the number of turns
in the respective coil is
A . 1: 5
B. 5: 1
c. 25: 1
D. 1: 25
12
186 The ratio of the peak current through the capacitor and supply is known-as:
A. Resonance current
B. Dynamic resistance
c. Q-factor
D. None of the above
12
187 5. In an oscillating LC circuit, the maximum charge in
the capacitor is Q. The charge on the capacitor when
the energy is stored equally between the electric and
magnetic fields is
(a) e
SONO
(AIEEE 2003)
12
188 The capacitive reactance of ( 50 mu mathrm{F} )
capacitance at a frequency of ( 2 times 10^{3} )
( mathrm{Hz} ) will be ( _{—-} Omega )
( A cdot frac{2}{pi} )
B. ( frac{3}{pi} )
( c cdot frac{4}{pi} )
( D cdot frac{5}{5} )
12
189 The capacitive reactance in an ( A C ) circuit is
A. effective resistance due to capacity
B. effective wattage
c. effective voltage
D. None of these
12
190 An inductive coil has resistance of
100Omega. When an ac signal of frequency 1000 ( H z ) is fed to the coil, the applied
voltage leads the current by ( 45^{circ} . ) What
is the inductance of the coil?
( mathbf{A} cdot 2 m H )
в. 3.3 тН
c. ( 16 m H )
D. ( sqrt{5} ) m Н
12
191 A transmitter transmits at a
wavelength of ( 300 m . ) A condenser of
capacitance ( 2.4 mu F ) is being used. The
value of the inductance for the resonant
circuit is approximately
В . ( 10^{-6} ) Н
( mathrm{c} cdot 10^{-8} mathrm{H} )
D. ( 10^{-10} H )
12
192 The adjoining figure shows an ( boldsymbol{A C} )
circuit with resistance ( boldsymbol{R} ), inductance ( boldsymbol{L} )
and source voltage ( V_{s} . ) Then
A. the source voltage ( V_{s}=72.8 mathrm{V} )
B. the phase angle between current and source voltage is ( tan ^{-1}(7 / 2) )
c. Both ( (a) ) and
( ( b ) ) are correct.
D. Both ( (a) ) and
( (b) ) are wrong.
12
193 The given graph shows volume with
time in the source voltage and steady
state current drawn by a series ( boldsymbol{B} boldsymbol{L} boldsymbol{C} )
circuit:
Which of the following statements
is/are correct?
(a) Current lags the voltage.
(b) Resistance in the circuit is ( 250 sqrt{Omega} )
(c) Reactance in the circuit is ( 250 Omega )
(d) Average power dissipation in the
circuit is ( 20 sqrt{3 Omega} )
A. Only a
( B cdot a & b )
( c cdot a, b & c )
D. All
12
194 In the circuit shown in figure, key K is closed at t = 0,
the current through the key at the instant t = 10″ In 2 sis
422
50
— 20 V
EL=5 mH
522
ws
HA
622
(a) 2 A
(c) 2.5 A
C = 0.1 mF
(b) 3.5 A
(d) 0
12
195 For a series LCR circuit at resonance,
the statement which is not true is
A. Peak energy stored by a capacitor = peak energy stored by an inductor
B. Average power = apparent power
C. Wattless current is zero
D. Power factor is zero
12
196 toppr
Q Type your question_
( mathbf{A} )
( B )
( c )
( (c) )
( D )
12
197 Equation of current flowing towards left in the inductor 12
198 The ratio of the secondary to the primary turns in a transformer is 3: 2
and the output power is ( P . ) Neglecting
all power losses, the input power must be
A ( cdot frac{2 P}{3} )
в. ( frac{3 P}{2} )
c. ( frac{P}{2} )
D. ( P )
12
199 (i) Name the transformer used in the
power transmitting station of a power plant.
(ii) What type of current is transmitted
from the power station?
(iii) At what voltage is this current available to our household?
12
200 In an ideal parallel LC circuit, the capacitor is charged by connecting it to a DC source which is then disconnected
The current in the circuit
A. becomes zero instantaneously
B. grows monotonically.
c. decays monotonically.
D. oscillates instantaneously
12
201 maximum current that will flow in the
circuit
12
202 19. In an ac circuit, the potential differences across an inductance
and resistance joined in series are, respectively, 16 V and
20 V. The total potential difference across the circuit is
(a) 20 V
(b) 25.6 V
(c) 31.9 V
(d) 53.5 V
12
203 An AC source is connected in parallel
with an L-C-R circuit as shown. Let
( I_{S}, I_{L}, I_{C} ) and ( I_{R} ) denote the currents
through and ( V_{S}, V_{L}, V_{C} ) and ( V_{R} )
voltages across the corresponding
components. Then:
A ( cdot I_{S}=I_{L}+I_{C}+I_{R} )
В. ( V_{S}=V_{L}+V_{C}+V_{R} )
( mathbf{c} cdotleft(I_{L}, I_{C}, I_{R}right)<I_{S} )
D. ( I_{L}, I_{C} ) may be greater than ( I_{S} )
12
204 Assertion (A): More the turns more is
the
resistance
Reason(R): Impedance of primary and secondary in a transformer is directly proportional
to number
of turns in the coils.
A. Both Assertion and Reason are true and Reason is the correct explanation for Assertion
B. Assertion and Reason are true but Reason is not the correct explanation for Assertion
C. Assertion is true, Reason is false
D. Assertion is false, Reason is true
12
205 In the circle shown ( boldsymbol{L}=mathbf{1} boldsymbol{mu} boldsymbol{H}, boldsymbol{C}=mathbf{1} boldsymbol{mu} boldsymbol{F} )
and ( R=1 k Omega . ) They are connected in
series with a.c. source ( V=V_{0} sin omega t ) as
shown.Which of the following option
is/are correct?
This question has multiple correct options
A. The frequency at which the current will be in the phase with the voltage is independent of ( R )
B. At ( omega sim 0 ) the current flowing through the circuitt
becomes nearly zero
C. ( A t omega>>10^{6} r a d . s^{-1}, ) the circuit behave like a capacitor
D. The current will be in phase with the voltage if ( omega= ) ( 10^{4} r a d cdot s^{-1} )
12
206 A power transformer has 50 turns for
primary and 300 turns for secondary. What is turns ratio? How much is
secondary voltage with primary voltage of ( 230 V ? )
12
207 ( A 20 V, 750 mathrm{Hz} ) source is connected to a
series combination of ( mathrm{R}=100 Omega, mathrm{C}=10 )
( mu F ) and ( L=0.1803 H . ) Calculate the time
in which resistance will get heated by
( 10^{circ} mathrm{C} . ) (If thermal capacity of the
material ( =2 mathrm{J} /^{circ} mathrm{C} )
A. 328 sec
B. 348 sec
c. ( 3.48 mathrm{sec} )
D. ( 4.32 mathrm{sec} )
12
208 The impedance of a series L-C-R circuit
in an AC circuit is
A ( cdot sqrt{R+left(X_{L}-X_{C}right)} )
B . ( sqrt{R^{2}+left(X_{L}^{2}-X_{C}^{2}right)} )
( c cdot c )
D. None of these
12
209 In a series LCR circuit, resoanance frequency if half of the frequency of source. The nature of the circuit is
A. Capacitive
B. Resistive
c. Inductive
D. cannot be defined
12
210 In AC circuit having only capacitor, the
current
A ( cdot ) Leads the voltage by ( frac{pi}{2} ) in phase
B cdot Lags behind the voltage by ( frac{pi}{2} ) in phase
C. Leads the voltage by ( pi ) in phase
D. Lags behind the voltage by ( pi ) in phase
12
211 In a circuit, ( L, C ) and ( R ) are connected in series with an alternating voltage source of frequency ( f ). The current leads
the voltage by ( 45^{circ} . ) The value of ( C ) is :
A ( frac{1}{pi f(2 pi f L+R)} )
в. ( frac{1}{pi f(2 pi f L-R)} )
c. ( frac{1}{2 pi f(2 pi f L+R)} )
D. ( frac{1}{2 pi f(2 pi f L-R)} )
12
212 The primary coil of a step-down transformer has number of
turns
A. more
B. less
c. same
D. None of the above
12
213 If the equations of alternating voltage and alternating current in an A.C. circuit
( operatorname{are} boldsymbol{E}=boldsymbol{E}_{0} sin omega boldsymbol{t} ) volt and ( boldsymbol{I}= )
( I_{0} sin (omega t-pi / 2) ) ampere
respectively. The power loss in the circuit will be
A . zero
в. ( frac{E_{0} I_{0}}{sqrt{2}} )
c. ( frac{E_{0} I_{0}}{2} )
D. ( frac{E I}{sqrt{2}} )
12
214 An ( L-C-R ) series circuit has a
maximum current of ( 5 A . ) If ( L=0.5 H )
and ( C=8 mu F, ) then the angular
frequency of ( boldsymbol{A} boldsymbol{C} ) voltage is :
A. 500 rad/s
B. 5000 rad/s
c. 400 rad/s
D. ( 250 mathrm{rad} / mathrm{s} )
12
215 When a coil is connected to a ( 100 mathrm{V} ) d
supply. The current is 2 A. When the same coil is connected to a.c. source ( E=100 sqrt{2} sin omega t, ) the current is ( 1 A )
Find the inductive reactance used :
12
216 36. Which voltmeter will give zero reading at resonance?
mH
(a) V
(c) và
(b) V2
(d) None
12
217 In an A.C. circuit, the current flowing in
inductance is ( boldsymbol{I}=mathbf{5} sin (mathbf{1 0 0} boldsymbol{t}-boldsymbol{pi} / mathbf{2}) )
amperes and the potential difference is
( boldsymbol{V}=mathbf{2 0 0} sin (mathbf{1 0 0} boldsymbol{t}) . ) The power
consumption is equal to
A. 1000 watt
B. 40 watt
c. 20 watt
D. zero
12
218 Find the In the circuit shown in Fig,
switch ( S_{1} ) was closed for a long time. At
time ( t=0 ) the switch is
opened. Angular frequency of oscillation of the charge on the capacitor:
A ( cdot 100 operatorname{rad} s^{-1} )
B. 200 rads( ^{-1} )
c. 300 rads( ^{-1} )
D. 400 rads( ^{-1} )
12
219 State whether given statement is True or False
A lower Q produces a narrower bandwidth.
A. True
B. False
12
220 A transformer used to reduce the
alternating voltage is :
A. Step-up transformer
B. Step-down transformer
c. Both step-up and step-down transformers
D. None of these
12
221 A series ( L C R ) circuit is connected to a
source of alternating emf ( 50 mathrm{V} ) and if the potential differences across inductor and capacitor are ( 90 mathrm{V} ) and
( 60 V ) respectively, the potential
difference across resistor is:
( mathbf{A} cdot 400 V )
в. ( 40 V )
( c .80 V )
D. ( 1600 V )
12
222 A sinusoidal voltage ( V=200 sin 314 t )
is appiled to a ( 10 Omega ) resistor. Find (i)
rms voltage
(ii) rms current and (iii)
power dissipated as heat.
12
223 In the circuit diagram shown, ( X_{C}= )
( mathbf{1 0 0 Omega}, boldsymbol{X}_{L}=mathbf{2 0 0 Omega} & boldsymbol{R}=mathbf{1 0 0 Omega} . ) The
effective current through the source is:
( A cdot 2 A )
B. ( 2 sqrt{2} A )
( c cdot 0.5 mathrm{A} )
D. ( sqrt{0.4 A} )
12
224 57. For an LCR series circuit with an ac source of angular
frequency o,
(a) circuit will be capacitive if o >
(b) circuit will be inductive if m=-
vec
(c) power factor of circuit will be unity if capacitive
reactance equals inductive reactance
(d) current will be leading voltage if o >-
VLC
12
225 In a step up transformer
A. ( N_{s}=N_{p} )
B. ( N_{s}N_{p} )
D. nothing can be said.
12
226 Assertion
When a current flows in the coil of a
transformer then its core becomes hot.
Reason

The core of transformer is made of soft-
iron.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

12
227 In the transmission of power the voltage of power generated at the generating stations is stepped up from ( 11 mathrm{kV} ) to 132 kV before it is transmitted. Why? 12
228 are rixed at separatıon or ( boldsymbol{a} ) trom eacn
other as shown. The area of each plate is
A. Plate 1 is given charge ( +Q ) while
plate 2 and 3 are neutral and are
connected to each other through coil of inductances ( L ) and switch ( S . ) If
resistance of all connected wires is
neglected the maximum current flow, through coil after closing switch is
( left(boldsymbol{C}=varepsilon_{0} boldsymbol{A} / boldsymbol{d}right) ) (neglect fringe effect)
A ( cdot frac{Q_{0}}{sqrt{L C}} )
в. ( frac{Q_{0}}{sqrt{2 L C}} )
c. ( frac{2 Q_{0}}{sqrt{L C}} )
D. ( frac{Q_{0}}{2 sqrt{L C}} )
12
229 A coil of inductance ( 0.50 H ) and
resistance ( 100 Omega ) is connected to a
( 240 V, 50 H z ) ac supply. The maximum current in the coil is given as ( frac{x}{100} A ) Find ( x )
12
230 A series LCR circuit containing a
resistance of ( 120 Omega ) has angular resonance frequency ( 4 times 10^{5} ) rad ( s^{-1} )
At resonance the voltage across the
resistance and inductance are ( 60 mathrm{V} ) and
( 40 mathrm{V} ) respectively. The angular frequency at which current in the circuit lags the
voltage by ( 45^{0} ) is
A ( cdot 16 times 10^{5} ) rad ( s^{-1} )
B. ( 8 times 10^{5} ) rad ( s^{-1} )
C . ( 4 times 10^{5} ) rad ( s^{-1} )
D. ( 2 times 10^{5} ) rad ( s^{-1} )
12
231 A step up transformer operates on a
( 230 V ) line and supplies to a load ( 2 A )
The ratio of primary to secondary
windings is ( 1: 25 . ) Determine the
primary current.
A . ( 8.8 A )
B . ( 12.5 A )
c. ( 25 A )
D. ( 50 A )
12
232 A capacitance of ( left(frac{10^{-3}}{2 pi}right) F ) and an inductance of ( left[frac{100}{pi}right] m H ) and ( a ) resistance of ( 10 Omega ) are connected in
series with an AC voltage source of ( 220 V, 50 H z . ) The phase angle of the circuit is
A . ( 60^{circ} )
B. ( 30^{circ} )
( mathbf{c} cdot 45^{circ} )
D. ( 90^{circ} )
12
233 A ( 100 m H ) inductor, a ( 25 mu F ) capacitor
and a ( 15 Omega ) resistor are connected in
series to a ( 120 V, 50 H z ) ac source.
Calculate
(a) impedance of the circuit at
resonance
(b) current at resonance
(c) resonant frequency
A ( . ) (a) ( 16 Omega ) (b) ( 9 A ) (c) ( 100 H z ) ( z )
B. (a) ( 15 Omega ) (b) ( 8 A ) (с) ( 100 H z )
c. ( (text { a) } 15 Omega )
(b) ( 8 A ) (с) ( 120 H z )
D. (a) ( 15 Omega ) (b) ( 7 A ) (с) ( 100 H z )
12
234 Complete the following diagram in Fig. of a transformer and name the parts
labelled ( A ) and ( B ). Name the part you
have drawn to complete the diagram
What is the material of this part ? Is
this transformer a step-up or step-down
? Give reason.
12
235 COLOCUPUOIO
44. An rms voltage of 110 V is applied across a series circuit
having a resistance 11 2 and an impedance 22 12. The
power consumed is
(a) 275 W
(b) 366 W
(c) 550 W
(d) 1100 W
12
236 How is the e.m.f. across primary and
secondary coils of a transformer related
with the number of turns of coil in
them?
12
237 A ( 50 W, 100 V ) lamp is to be connected to an AC mains of ( 200 mathrm{V}, 50 mathrm{Hz} ). What capacitor is essential to be put in series with the lamp?
A ( cdot frac{25}{sqrt{2}} mu F )
в. ( frac{50}{pi sqrt{3}} mu F )
c. ( frac{50}{sqrt{2}} mu F )
D. ( frac{100}{pi sqrt{3}} mu F )
12
238 A circuit operating at ( frac{360}{2 pi} mathrm{Hz} Omega ) contains a ( 1 mathrm{F} mu ) capacitor and a 20 resistor. The inductor must be added in
series to make the phase angle for the circuit zero is
A . 7.7
B. 10
c. ( 3.5 mathrm{H} )
D. 15 H
12
239 Potential difference across capacitor of
capacitance 3C when the current in the circuit is maximum is
( A cdot frac{3 V_{0}}{4} )
B. ( frac{V_{0}}{4} )
( c cdot frac{5 V_{0}}{4} )
D. none of these
12
240 Assertion: Faraday’s laws are consequences of conservation of energy Reason: In a purely resistive A.C. circuit
the current lags behind the e.m.f. in
phase
A. If both assertion and reason are true but the reason is the correct explanation of assertion.
B. If both assertion and reason are true but the reason is not the correct explanation of assertion
c. If assertion is true but reason is false
D. If both the assertion and reason are false.
E. If reason is true but assertion is false
12
241 In the shown circuit, ( boldsymbol{R}_{1}=mathbf{1 0 Omega}, boldsymbol{L}= )
( frac{sqrt{3}}{10} H, R_{2}=20 Omega, C=frac{sqrt{3}}{2} ) milli
farad and ( t ) is time in seconds. Then at
the instant current through
( boldsymbol{R}_{1} boldsymbol{i} boldsymbol{s} mathbf{1} boldsymbol{0} sqrt{boldsymbol{2}} boldsymbol{A} )
find the current through resistor ( boldsymbol{R}_{2} ) in
amperes.
12
242 Comparing the L-C oscillations with the oscillations of a spring block system (force constant of spring ( =k ) and mass
of the block ( =m ) ), the physical quantity
( m k ) is equal to :
A . ( C L )
в. ( 1 / C L )
c. ( C / L )
D. ( L / C )
12
243 A resistor, an indicator and a capacitor are connected in series with a ( 120 mathrm{V}, 100 ) ( mathrm{Hz} ) ac source. Voltage leads the current
by ( 35^{circ} ) in the circuit. If the resistance of
the resistor is ( 10 Omega ) and the sum of
inductive and capacitive reactance is ( 17 Omega, ) calculate the self-inductance of
the inductor.
12
244 The source frequency for which a ( 5 mu mathrm{F} )
capacitor has a reactance of ( 1000 Omega ) is
A ( cdot frac{100}{pi} ) Hz
в. ( frac{1000}{pi} ) Н ( z )
( c .200 H z )
D. ( 5000 mathrm{Hz} )
12
245 What is the mechanical equivalent of spring constant ( mathrm{k} ) in ( mathrm{LC} ) oscillating circuit?
A ( cdot frac{1}{L} )
в. ( frac{1}{C} )
c. ( frac{L}{C} )
D. ( frac{1}{L C} )
12
246 Find the maximum value of current
when inductance of two henry is connected to ( 150 V, 50 ) cycle supply
( ^{mathrm{A}} cdot frac{3}{2 sqrt{2} A} )
B. ( frac{5}{2 sqrt{2} A} )
c. ( frac{6}{2 sqrt{2} A} )
D. ( frac{7}{2 sqrt{2} A} )
12
247 A ( 12 Omega ) resistor, a ( 40 mu F ) capacitor, and
an ( 8 m H ) coil are in series across an ac
source. The resonant frequency is
A ( .28 .1 H z )
в. ( 281 mathrm{Hz} )
( mathbf{c} cdot 2,810 H z )
D. ( 10 H z )
12
248 At resonance, the angle ( phi ) is
A.
B. ( frac{pi}{2} )
c. ( frac{pi}{6} )
D. zero
12
249 The average power dissipated in a pure inductance is
( ^{mathbf{A}} cdot frac{1}{2}^{L I^{2}} )
B . ( L I^{2} )
c. ( L I^{2} / 4 )
D. zero
12
250 If we increase the driving frequency in a circuit with a purely resistive load, then
amplitude ( V_{R} )
A. remain in the same
B. increase
c. decrease
D. none
12
251 When ( 10 V, D C ) is applies across a coil
current through it is ( 2.5 mathrm{A}, ) if ( 10 mathrm{V}, 50 mathrm{Hz} mathrm{A} )
C. is applied current reduces to 2 A. Calculate reluctance of the coil.
12
252 In an ac circuit, ( mathrm{V} ) and I are given by ( boldsymbol{V}=mathbf{1 5 0} sin (mathbf{1 5 0} boldsymbol{t}) boldsymbol{V} boldsymbol{a n d} boldsymbol{I}= )
( 150 sin left(150 t+frac{pi}{3}right) A )
The power dissipated in the circuit is
A . ( 106 mathrm{w} )
B. 150 ( mathrm{w} )
c. ( 5625 mathrm{w} )
D. zero
12
253 19. A fully charged capacitor C with initial charge qo is
connected to a coil of self inductance L at t = 0. The time
at which the energy is stored equally between the electric
and the magnetic fields is
(a) VLC
(b) JLC
(c) 27 VLC (d) VLC (AIEEF 11)
12
254 In the above circuit, ( C=frac{sqrt{3}}{2} mu F, R_{2}= ) ( 20 Omega, L=frac{sqrt{3}}{10} H ) and ( R_{1}=10 Omega . ) Current
( operatorname{in} L-R_{1} ) path is ( I_{1} ) and in ( C-R_{2} ) path
it is ( I_{2} ). The voltage of ( A . C ) source is ( operatorname{given} operatorname{by} V=200 sqrt{2} sin (100 t) ) volts.
The phase difference between ( I_{1} ) and ( I_{2} )
is
A ( cdot 30 )
B . ( 0^{circ} )
( c cdot 150 )
D. 60
12
255 12. Same current is flowing in two alternating circuits. The
first circuit contains only inductance and the other contains
only a capacitor. If the frequency of the e.m.f. of ac is
increased, the effect on the value of the current will be
(a) Increases in the first circuit and decreases in the other
(b) Increases in both the circuits
(c) Decreases in both the circuits
(d) Decreases in the first circuit and increases in the other
12
256 A radio can tune over the frequency range of a portion of MW broadcast
band: ( (800 mathrm{kHz} text { to } 1200 mathrm{kHz} ) ). If its LC
circuit has an effective inductance of
( 200 mu mathrm{H}, ) what must be the range of its variable capacitor? [Hint: For tuning, the natural frequency
i.e., the frequency of free oscillations of
the LC circuit should be equal to the frequency of the radiowave.]
12
257 In series ( L-R ) circuit, ( X_{L}=R ). Now a
capacitor with ( X_{C}=R ) added in series.
New power factor:
A. Same as initial
B. ( frac{1}{sqrt{2}} ) times the initial
c. ( frac{1}{2} ) times the initial
D. ( sqrt{2} ) times the initial
12
258 the maximum energy so
66. The natural frequency of the circuit shown in figure is

TH
VLC
70
L
Vzic
llllll
llllll
(d) none of these
Problems Based on Mixed Concepts
12
259 A series LCR circuit is connected to an
a.c. source of variable frequency. Draw a suitable phasor diagram to deduce the expressions for the amplitude of the current and phase angle.
12
260 An LC circuit has ( L=5 mathrm{mH} ) and ( mathrm{C}=20 mu boldsymbol{F} )
( boldsymbol{V}=mathbf{5} times mathbf{1 0}^{-3} ) coswt is supplied. ( boldsymbol{omega} ) is
twice the resonant frequency. Find the maximum charge stored in the capacitor.
A. 66.6 nc
B. 11.3 nC
c. 23.2 nc
D. 33.3 nc
12
261 The average half-cycle value of a sine
wave with a ( 40 V ) peak is
A . ( 25.48 V )
B . ( 6.37 V )
c. ( 14.14 V )
D. ( 50.96 V )
12
262 (a) The voltage leads the current by it
8. A direct current of 5 A is superimposed on an alternating
current I=10 sin ot flowing through a wire. The effective
value of the resulting current will be
(a) (15/2) A
(b) 53A
(c) 5√5A
(d) 15 A
mont of uolueamnare is cuina
ܘܘܘܘ
12
263 A ( 300 Omega ) resistor, a ( 0.250 H ) inductor
and a ( 8.00 mu F ) capacitor are in series
with an ac source with voltage amplitude ( 120 V ) and angular frequency ( 400 r a d / s . ) Which of the following is/are
correct?
This question has multiple correct options
A. Voltage amplitude across the resistor is ( 97.9 V )
B. Voltage amplitude across the inductor is ( 32.6 mathrm{V} )
c. voltage amplitude across the capacitor is ( 102 V )
D. Voltage amplitude across the resistor is ( 32.6 V )
12
264 15. Using an ac voltmeter, the potential difference in the elec-
trical line in a house is read to be 234 V. If the line fre-
quency is known to be 50 cycles per second, the equation
for the line voltage is
(a) V= 165 sin(100 mt) (b) V = 331 sin(100 Tot)
(c) V=220 sin(100 mt) (d) V = 440 sin(100 Tt)
12
265 A ( 220 mathrm{V} ) main supply is connected to a resistance of ( 100 mathrm{k} Omega ). The effective
current is?
A. ( 2.2 mathrm{mA} )
B. ( 2.2 sqrt{2} mathrm{mA} )
c. ( frac{2.2}{sqrt{2}} mathrm{m} )
D. None of these
12
266 In a step-down transform the turn ratio is 1: 2 and output power is ( 2.2 k W ). if
output current is ( 10 A ) then the value of
input voltage and input current:
A. ( 100 V, 20 A )
в. ( 110 V, 10 A )
c. ( 440 V, 5 A )
D. ( 440 V, 20 A )
12
267 In a transformer, there are 10000 turns
in the primary coil and 25000 turns in the secondary coil.An AC EMF ( e= )
( 50 sin pi t ) is applied across primary coil
,find the peak EMF across the secondary coil in ideal conditions
12
268 An ideal resistance ( R ), ideal inductance
( L, ) ideal capacitance ( C ) and ( A C ) volt
meters ( V_{1}, V_{2}, V_{3} ) and ( V_{4} ) are
connected to an AC source as shown. At
resonance,
A. Reading in ( V_{3}= ) reading in ( V_{1} )
B. Reading in ( V_{1}= ) reading in ( V_{2} )
c. Reading in ( V_{2}= ) reading in ( V_{4} )
D. Reading in ( V_{2}= ) reading in ( V )
12
269 A steady current of magnitude ( I ) and an
( A C ) current of peak value ( I ) are allowed to pass through identical resistor for
the same time. The ratio of heat
produced in the two resistors will be :
A .2: 1
B. 1: 2
c. 1: 1
D. None of these
12
270 Assertion
According to Lenz Law, since the same
magnetic flux passes through both the primary and secondary windings in an ideal transformer,a voltage is induced
in each winding.
Reason
Voltage induced is same in both the
windings, ideally.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is incorrect but Reason is correct
D. Both Assertion and Reason are incorrect
12
271 The capacitor of an oscillatory circuit of negligible resistance is enclosed in a evacuated container. The frequency of the circuit is ( 150 mathrm{kHZ} ) and when the
container is filled with a gas, the frequency changes by 100 HZ. The dielectric constant of the gas.
( A cdot 2 )
B. 1.53
c. 1.0012
D. 3
12
272 The given graphs (a) and (b) represent the variation of the opposition offered by the circuit element to the flow of
alternating current, with frequency of the applied emf. Identify the circuit element corresponding to each graph.
12
273 In a black box of unknown elements ( (boldsymbol{L} ) or ( R ) or any other combination), an ac
voltage ( boldsymbol{E}=boldsymbol{E}_{0} sin (boldsymbol{omega} boldsymbol{t}+boldsymbol{phi}) ) is applied
and current in the circuit was found to
be ( boldsymbol{I}=boldsymbol{I}_{0} sin [boldsymbol{omega} boldsymbol{t}+boldsymbol{phi}+(boldsymbol{pi} / mathbf{4})] . ) Then the
unknown elements in the box may be
A. Only capacitor
B. Inductor and resistor both
c. Either capacitor, resistor, inductor or only capacito and resistor
D. only resistor
12
274 The potential difference across a ( 2 H )
inductor as a function of time is shown
in figure. At time ( t=0, ) current is zero
Current at ( t=2 ) second is:
A . ( 1 A )
в. 3 А
( c cdot 4 A )
D. ( 5 A )
12
275 ( A 60 mathrm{W} / 120 mathrm{V} ) bulb is connected to a
( 240 / 60 mathrm{Hz} ) supply with an inductance in series. Find the value of inductance so
that bulb gets correct voltage.
A ( cdot frac{2.3}{pi} ) н
в. ( 2 sqrt{3} ) н
с. ( pi ) н
D. ( frac{2 sqrt{3}}{pi} ) н
12
276 In the given circuit, initially ( boldsymbol{K}_{mathbf{1}} ) is
closed and ( K_{2} ) is open. Then ( K_{1} ) is
opened and ( K_{2} ) is closed. If ( q_{1}^{prime} ) and ( q_{2}^{prime} ) are
charges on ( C_{1} ) and ( C_{2} ) and ( V_{1} ) and ( V_{1} )
are the voltage respectively, then
A. charge on ( C_{1} ) gets redistributed such that ( V_{1}=V_{2} )
B. charge on ( C_{1} ) gets redistributed such that ( q_{1}^{prime}=q_{2}^{prime} )
C. charge on ( C_{1} ) gets redistributed such that ( C_{1} V_{1}= ) ( C_{2} V_{2}=C_{1} V )
D. charge on ( C_{1} ) gets redistributed such that ( q_{1}^{prime}+q_{2}^{prime}=2 q )
12
277 A coil of inductance ( 0.1 mathrm{H} ) is connected to
( 50 V, 100 H z ) generator and current is found to be 0.5A. The potential
difference across resistance of the coil
is
A . ( 15 v )
B. 20V
c. ( 25 v )
D. 39V
12
278 At resonance, what is the relation
between impedance of a series ( L C R ) circuit and its resistance ( boldsymbol{R} ) ?
12
279 What is meant by wattless component
of the current?
12
280 A capacitor ‘C’ is connected across a
D.C. source, the reactance of capacitor
will be
A . ZERO
в. Нाप्प
c. Low
D. INFINITE
12
281 Which of the following rejector circuit (symbols have their usual meaning)?
( A )
B.
( c )
D.
12
282 60. A typical light dimmer used to dim the stage lights in a
theatre consists of a variable induction for L (where
inductance is adjustable between zero and Lmax) connected
in series with a light bulb B as shown. The mains electrical
supply is 220 V at 50 Hz, the light bulb is rated at 220 V,
1100 W. What Lmax is required if en
the rate of energy dissipation in
Bulb
to mains
the light bulb is to be varied by a
factor of 5 from its upper limit of
1100 W?
(a) 0.69 H
(b) 0.28 H
(c) 0.38 H
(d) 0.56 H
12
283 ILLUSTRATION 24.4 In the series circuit of the figure, suppose
R= 300 12, L = 60 mH, C =0.50 uF,
source amplitude is Eo = 50 V and
0 = 10,000 rad – Find the
reactances XL and Xc, the impedance
Z, the current amplitude 1o, the phase
angle 0, and the voltage amplitude b
across each circuit element.
… Tid ative and conditive reactances are
12
284 A waveform has a baseline of ( 3 V ), a duty
cycle of ( 20 %, ) and an amplitude of ( 8 V )
The average voltage value is
A . ( 4 V )
в. ( 4.6 V )
c. ( 1.6 V )
D. ( 11 V )
12
285 The phase difference between the
applied emf and the line current in an
anti resonant circuit at resonance is
A ( cdot frac{pi}{2} ) radian
B. ( pi ) radian
c. ( frac{3 pi}{2} ) radian
D. zero
12
286 Assertion
In series ( boldsymbol{L}-boldsymbol{C}-boldsymbol{R} boldsymbol{A} boldsymbol{C} ) circuit, current
and voltage are in same phase at
resonance.
Reason
In series ( boldsymbol{L}-boldsymbol{C}-boldsymbol{R} boldsymbol{A} boldsymbol{C} ) circuit,
resonant frequency does not depend on the value of resistance. Hence current,
at resonance, does not depend on
resistance.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
287 A ( 1.5 mu F ) capacitor is charged of ( 60 V ) The charging battery is then disconnected and a ( 15 mathrm{mH} ) coil is
connected in series with the capacitor so that LC oscillations occurs. Assuming that the circuit contains no
resistance. The maximum current in
this coil shall be close to
A . 1.4 A
B. ( 1.2 A )
( c .0 .8 A )
D. 0.6 A
12
288 The capacitance of a capacitor whose reactance is ( 2.00 Omega ) at ( 50.0 H z ) is ( frac{x}{10} m F ) Find ( boldsymbol{x} ) 12
289 1. The power factor of an AC circuit having resistance R and
inductance L connected in series and an angular velocity
o is
R
(6)
(R² + w²L²) 1/2
R
(d) –
“(R² – w²L²) 1/2
(AIEEE 2002)
12
290 A ( 15.0 mu F ) capacitor is connected to a
( 220 V, 50 H z ) source. Find the
capacitive reactance and the current ( (mathrm{rms} text { and peak }) ) in the circuit. If the frequency is doubled, what happens to the capacitive reactance and the
current?
12
291 Of the following about capacitive
reactance which is correct?
A. The reactance of the capacitor is directly proportional to its ability to store charge
B. Capacitive reactance is inversely proportional to the frequency of the current
C . Capacitive reactance is measured in farad
D. The reactance of a capacitor in an AC circuit is similar to the resistance of a capacitor in a DC circuit
12
292 Define quality factor of resonance in
series LCR circuit.
12
293 In a purely resistive circuit:
A . current lags behind the voltage by ( 90^{circ} )
B. current leads the voltage by ( 90^{circ} )
C . current can lag or lead the voltage by ( 90^{circ} )
D. current is in phase with the voltage
12
294 ( A 750 H z, 20 V ) source is connected to a resistance of ( 100 Omega, ) an inductance of ( 0.1803 H ) and a capacitance of ( 10 mu F ) all
in series. Calculate the time in which
the resistance (thermal capacity
( left.2 J /^{o} Cright) ) will get heated by ( 10^{circ} mathrm{C} ). (lgnore radiation)
A . 6.8 min
B. 5.8 min
c. 7.8 min
D. 9.8 min
12
295 Using the expressions for charge and current for L-C oscillator, explain L-C oscillations. 12
296 A wire carrying ( 5.0 V ) is applied to a primary coil of the transformer. The
primary coil has 10 turns and the secondary coil has 20 turns. Find out the emf induced in the secondary coil?
( mathbf{A} cdot 0.50 V )
в. ( 5.0 V )
c. ( 10 V )
D. ( 50 V )
E . ( 100 V )
12
297 The self inductance of a choke coil is 10
mH. When it is connected with a 10 V
D.C. source, then the loss of power is 20
watt. When it is connected with 10 volt
A.C. source loss of power is 10 watt. The frequency of A.C. source will be.
A . 50 нz
в. 60 на
c. 80 Нz
D. 100 Н ( z )
12
298 In a series LCR circuit, resonance
occurring at ( 105 mathrm{Hz} ). At that time, the potential difference across the 100 resistance is ( 40 mathrm{V} ) while the potential difference across the pure inductor is 30v. The inductance L of the inductor is
equal to
A ( cdot 2.0 times 10^{-4} )
B . ( 3.0 times 10^{-4} )
c. ( 1.2 times 10^{-4} )
D. ( 2.4 times 10^{-4} )
12
299 The equation of an alternating voltage is ( V=100 sqrt{2} sin 100 pi t ) volt. The RMS
value of voltage and frequency will be respectively
A. ( 100 V, 50 H z )
в. ( 50 V, 100 H z )
c. ( 150 V, 50 H z )
D. ( 200 V, 50 H z )
12
300 The frequency of an alternating potential is ( 50 H z ), then the time difference corresponding to a phase
angle of ( 50^{circ} ) is
A . 60 sec
B. 1 sec
c. ( (1 / 60) ) sec
D. ( (1 / 360) ) sec
12
301 toppr
Q Type your question.
obtain expressions for impedance of the circuit and phase angle between voltage and current. Find the condition
when current will be in phase with the voltage. What is the circuit in this
condition called?
(ii) In a series LR circuit ( boldsymbol{X}_{L}=boldsymbol{R} ) and
power factor of the circuit is ( P_{1} ). When
capacitor with capacitance C such that
( X_{L}=X_{C} ) is put in series, the power
factor becomes ( P_{2} ). Calculate ( P_{1} / P_{2} )
OR
(i) Write the function of transformer.
state its principle of working with the help of a diagram. Mention various energy losses in this device.
(ii) The primary coil of an ideal step up transformer has 100 turns and
transformation ratio is also ( 100 . ) The
input voltage and power are respectively ( 220 mathrm{V} ) and ( 1100 mathrm{W} ). Calculate
(a) number of turns in secondary
(b) voltage across secondary
(c) current in primary
(d) current in secondary
(e) power in secondary
12
302 ILLUSTRATION 24.1 The plate on the back of a perso
computer says that it draws 2.7 A from a 120-V, 60-HI
For this computer, what is (a) the average of the square of the
current, (b) the current amplitude, (c) the average current for
positive half cycle, and (d) the average current for a full cycle
Solution
12
303 A condenser of ( 250 mu F ) is connected in parallel to a coil of inductance ( 0.16 mathrm{mH} ) while its effective resistance is ( 20 Omega )
Determine the resonant frequency.
A ( cdot 9 times 10^{4} H z )
B . ( 16 times 10^{7} mathrm{Hz} )
c. ( 8 times 10^{5} H z )
( mathbf{D} cdot 9 times 10^{3} H z )
12
304 Which of the following is correct for a
step up transformer?
( mathbf{A} cdot N_{s}=N_{p} )
В. ( N_{s}N_{p} )
D. Nothing can be said
12
305 26. When 100 V dc is applied across a solenoid, a current of
1.0 A flows in it. When 100 V ac is applied across the
same coil, the current drops to 0.5 A. If the frequency of
the ac source is 50 Hz, the impedance and inductance of
the solenoid are
(a) 200 22 and 0.55 H (b) 100 22 and 0.86 H
(c) 200 22 and 1.0 H (d) 100 22 and 0.93 H
12
306 от России
56. In the circuit shown in the figure, Xc= 100 S2, XL = 200 S2
and R=100 2. The effective current through the source is
M
200 v
)
(a) 2 A
(c) 0.5 A
(b) 212 A
(d) 10.4 A
12
307 A transmitter transmits at a wave
length of 300 meters. A capacitor of a
capacitance ( 9.6 mu mathrm{F} ) is being used. The value of the inductance for the resonant
circuit is approximately
A . 2.5 ( mathrm{mH} )
в. 2.5 ( mu ) Н
c. 2.5 n
D. 2.5 ph
12
308 ( ln ) an ( L C ) oscillation circuit, ( L= )
( mathbf{1} boldsymbol{H}, boldsymbol{C}=frac{mathbf{1}}{mathbf{4}} boldsymbol{F} ) and maximum charge in
capacitor is ( 4 C . ) Match the following two
columns. Note that in column II all
values are in their respective Sl units
12
309 For an ideal step-down transformer, the
quantity which is constant for both the coils will be
A. current in the coils
B. voltage across the coils
c. resistance of coils
D. power in the coils
12
310 In an oscillating LC circuit the maximum charge on the capacitor is ( Q )
The charge on capacitor when the energy is stored equally between electric and magnetic field is :
( mathbf{A} cdot Q / 2 )
в. ( Q / sqrt{3} )
c. ( Q / sqrt{2} )
D. ( Q )
12
311 21. A capacitor of 10 uF and an inductor of 1 H are joined
in series. An ac of 50 Hz is applied to this combination.
What is the impedance of the combination?
(a) 5(17+ – 5), (b) 10(10–īt?),
TT
(c) 10(T? – 5), (d) 5(10–17?),
12
312 An alternating voltage (in volts) given by ( V=200 sqrt{2} sin (100) t ) is connected
to ( 1 mu F ) capacitor through an ideal ac ammeter in series. The reading of the
ammeter and the average power consumed in the circuit shall be
A ( .20 m A, 4 W )
в. ( 20 m A, 0 )
c. ( 20 sqrt{2} m A, 8 W )
D. ( 20 sqrt{2} mathrm{mA}, 4 sqrt{2} mathrm{W} )
12
313 When an ac source of voltage ( boldsymbol{V}= )
( V_{0} sin 100 t ) is connected across a
circuit, the phase difference between
the voltage ( V ) and current lin the circuit
is observed to be ( pi / 4, ) as shown in
figure. If the circuit consists
possibly only of RC or RL or LC in series,
find possible values of two elements.
A ( . R=1 k Omega, C=10 mu F )
B. ( R=1 k Omega, C=1 mu F )
c. ( R=1 k Omega, L=10 m H )
D. ( R=10 k Omega, L=10 m H )
12
314 The angular frequency of an AC source is 10 radian/sec. The reactance of ( 1 mu F ) capacitor will be
A ( cdot 10^{4} Omega )
B . ( 10^{2} Omega )
( mathbf{c} cdot 10^{1} Omega )
D. ( 10^{5} Omega )
12
315 A capacitor of capacitance ( C ) has initial
charge ( Q_{0} ) and connected to an inductor
of inductance ( L ) as shown. At ( t=0 ) switch
S is closed. The current through the inductor when energy in the capacitor is three times the energy of inductor is
A ( cdot frac{Q_{0}}{2 sqrt{L C}} )
в. ( frac{Q_{0}}{sqrt{L C}} )
c. ( frac{2 Q_{0}}{sqrt{L C}} )
D. ( frac{4 Q_{0}}{sqrt{L C}} )
12
316 In a purely resistive ( boldsymbol{A C} ) circuit
A. voltage leads current
B. voltage lags current
C . voltage and current are in same phase
D. nothing can be said
12
317 In the given circuit ( R ) in pure resistance
and ( X ) is unknown circuit element. An
AC voltage source is applied across ( boldsymbol{A} )
and ( C . ) If ( V_{A B}=V_{A C}, ) then ( X ) is
A. Pure resistance
B. Pure inductance
C. Combination of inductance and capacitance at
resonance
D. None of the above
12
318 9. Find out the amount of charge flown through the wire at
seconds.
(a) 3 coulombs
(c) 1 coulomb
(b) 6 coulombs
(d) Zero coulomb
12
319 If in a series L-C-R ac circuit, the
voltages across ( L, C ) and ( R ) are ( V_{1}, V_{2} )
and ( V_{3} ) respectively, then the voltage
of the source is always
A. equal to ( V_{1}+V_{2}+V_{3} )
B. equal to ( V_{1}-V_{2}+V_{3} )
c. more than ( V_{1}+V_{2}+V_{3} )
D. none of the above is true
12
320 ( ln L-C-R operatorname{series} ) circuit, the
capacitor is changed from ( C ) to ( 4 C ). For
the same resonant frequency, the inductance should be changed from
( boldsymbol{L} ) to
A ( .2 L )
в. ( frac{L}{2} )
c. ( frac{L}{4} )
D. ( 4 L )
12
321 Obtain the relation ( boldsymbol{I}=boldsymbol{I}_{0} sin (boldsymbol{omega} boldsymbol{t}+boldsymbol{pi} / mathbf{2}) )
and ( X_{C}=1 / omega C ) for a pure capacitor
across which an altering ( e m f=V= )
( V_{0} sin omega t ) is applied. Draw a phasor
diagram showing emf ( V ), current ( I ) and
their phase difference ( phi )
12
322 A 220 volt input is supplied to a transformer. The output circuit of
2.0 ampere at 440 volts. If the efficiency of the transformer is ( 80 % ), the current drawn by the primary windings of the transformer is
12
323 An inductor, a resistor and a capacitor are joined in series with an ( A C ) source. As the frequency of the source is
slightly increased from a very low value,
the reactance
A. of the inductor increases
B. of the resistor increases
c. of the capacitor increases
D. of the circuit increases
12
324 The natural frequency ( left(omega_{0}right) ) of
oscillations in LC Circuit is given by:
A ( cdot frac{1}{2 pi} frac{1}{sqrt{L C}} )
B. ( frac{1}{pi} frac{1}{sqrt{2 L C}} )
c. ( frac{1}{sqrt{L C}} )
D. ( sqrt{L C} )
12
325 The current which does not contribute
to the power consumed in an AC circuit is called:
A. Non-ideal current
B. Wattless current
c. convectional current
D. Inductance current
12
326 In the given LCR series circuit. Choose the correct option/options (resistance
is nonzero).
A. Reading of Voltmeter ( V_{2} ) may be greater than source
voltage
B. Reading of voltmeter ( V_{4} ) may be equal to ( V_{1} )
C. Reading of ( V_{4} ) may be equal to source voltage ( v )
D. None of these
12
327 In an LCR circuit, the capacitance is made one-fourth, when in resonance. Then what should be the change in inductance, so that the circuit remains
in resonance?
A. 4 times
B. (1/4) times
( c .8 ) times
D. 2 times
12
328 Calculate resonant frequency and ( Q )
factor of a series L-C-R circuit
containing a pure inductor of inductance ( 3 mathrm{H} ), Capacitor of
capacitance ( 27 mu F ) and resistor of resistance ( 7.4 Omega )
12
329 What is ( Q ) -factor? Write its expression
and write the conditions for its
maximum value.
12
330 The impedance of a pure anti-resonant
circuit at resonance is
A . zero
B. infinity
( c cdot 1 )
D. ( frac{1}{2} )
12
331 An inductive circuit contains
resistance of 10 ohms and an
inductance of ( 20 mathrm{H} ). If an A.c voltage of 120 volt and frequency ( 60 mathrm{Hz} ) is applied to this circuit, the current would be
nearly
A. ( 0.16 a m p )
B. ( 0.3 a m p )
c. ( 0.48 a m p )
D. ( 0.80 a m p )
12
332 An alternating voltage of ( 220 V, 50 H z ) frequency is applied across a capacitor of capacitance ( 2 mu F ). The impedence of
the circuit is:
A ( frac{pi}{5000} )
в. ( frac{1000}{pi} )
( c .500 pi )
D. ( frac{5000}{pi} )
12
333 A blackbox (BB) which may contain a
combination of electrical circuit
elements (resistor capacitor or
inductor) is connected with other
external circuit elements as shown
below in the figure (a).After the switch(s) is closed at time ( t=0, ) the
current (I) as a function of time (t) is
shown in the figure (b).
From this we can infer that the blackbox
contains
A. A resistor and a capacitor in series.
B. A resistor and a capacitor in parallel.
c. A resistor and an inductor in series
D. A resistor and an inductorin parallel.
12
334 The primary winding of a transformer
has 500 turns whereas its secondary has 5000 turns. The primary is connected to an ac supply of ( 20 vee, 50 mathrm{Hz} ) What will be the output of the secondary?
A ( .200 vee, 50 ) Н ( z )
в. ( 100 vee, 50 ) Н ( z )
c. ( 200 vee, 500 ) Н ( z )
D. 250 V, 50 нz
12
335 A box contains ( L, C ) and ( R ). When ( 250 V ) dc
is applied to the terminals of the box, a
current of ( 1.0 A ) flows in the circuit.
When ac source of ( 250 mathrm{V} ) rms at
( 2250 r a d / s ) connected, a current of
( 1.25 A mathrm{rms} ) flows. It is observed that the
current rises with frequency and becomes maximum at 4500 rad/s. Find
the values of ( L, C ) and ( R . ) Draw the circuit
diagram.
12
336 Voltage ( V ) and current i in AC circuit is given by ( mathrm{V}=mathbf{5 0} sin (mathbf{5 0} t) ) volt
( mathrm{i}=50 sin left(50 t+frac{pi}{3}right) m A . ) The power
dissipated in circuit is:
( mathbf{A} cdot 5.0 W )
B . ( 2.5 W )
c. ( 1.25 W )
D. zero
12
337 In a transformer, the number of turns of
primary coil and secondary coil are 5 and 4 respectively. If ( 220 mathrm{V} ) is applied on the primary coil, then the ratio
of primary current to the secondary current is :
A .4: 5
B. 5: 4
( c cdot 5: 9 )
D. 9 : 5
12
338 A condenser of capacity ( C ) is charged to
a potential difference of ( V_{1} . ) The plates
of the condenser are the connected to
an ideal inductor of inductance ( L ). The
current through the inductor when the
potential difference across the
condenser reduces to ( V_{2} ) is
( ^{mathbf{A}} cdotleft(frac{Cleft(V_{1}^{2}-V_{2}^{2}right)}{L}right)^{1 / 2} )
( ^{mathbf{B}} cdotleft(frac{Cleft(V_{1}-V_{2}right)}{L}right)^{1 / 2} )
( ^{mathbf{C}} cdot frac{Cleft(V_{1}^{2}-V_{2}^{2}right)}{L} )
D. ( frac{Cleft(V_{1}-V_{2}right)}{L} )
12
339 An alternating voltage ( boldsymbol{V}=boldsymbol{V}_{0} sin omega boldsymbol{t} ) is
applied across a circuit and as a result, a current ( boldsymbol{I}=boldsymbol{I}_{0} sin left(boldsymbol{omega} boldsymbol{t}+frac{boldsymbol{pi}}{2}right) ) flows in it
The power consumed per cycle is
A . ( I_{0} V_{0} )
в. ( 0.5 I_{0} V_{0} )
c. ( 0.7 I_{0} V_{0} )
D. ( 1.41 I_{0} V_{0} )
( E . )
12
340 A capacitor of ( 20 mu F ) is connected in
series with a ( 25 Omega ) resistance to a peak
e.m.f ( 240 v, 50 H z ) A.c. Calculate
(i)the capacitive reactance of the
circuit.
(ii)an impedance of the circuit
12
341 The applied potential difference in the
circuit shown is ( V=10 sin 100 t ) where
( V ) is in volt and ( t ) is in second. If the
power factor of the circuit is ( frac{1}{sqrt{2}}, ) then
the value of capacitance ( C ) of the
circuit, nearly is:
A. ( 111 mu F )
в. ( 333 mu F )
c. ( 222 mu F )
D. ( 444 mu F )
12
342 The instantaneous potential difference between points ( A ) and ( B ) is (Phase angle
is ( left.37^{0}right) )
A ( cdot 8 sin left(50 pi t+37 frac{pi}{180}right) )
B. ( 8 sin left(50 pi t-37 frac{pi}{180}right) )
c. ( 10 sin (50 pi t) )
D. ( 10 cos (50 pi t) )
12
343 4. In the above question the average value of voltage (V) in
one time period will be
(d) zero
12
344 If the inductance ( L ) in an oscillating ( L C ) circuit having a given maximum charge ( Q ) is increased, then
A. the current magnitude increases
B. the maximum magnetic energy increases
c. othere maximum magnetic energy decreases
D. currentt magnitude and maximum magnetic energy remain constant
12
345 The diagram given show the variation of
voltage and current in an AC circuit. The circuit contains
A. Only a resistor
B. Only a pure inductor
c. Only a capcacitor
D. A capacitor and and inductor
12
346 Rms value of current ( boldsymbol{i}=mathbf{3}+ )
( 4 sin left(omega t+frac{pi}{3}right) ) is:
A . ( 5 A )
в. ( sqrt{17} A )
( c cdot frac{5}{sqrt{2}} A )
D. ( frac{7}{sqrt{2}} A )
12
347 The voltage and the current of an a.c circuit are ( V=100 sin (100 t) ) volt and
( boldsymbol{i}=mathbf{1 0 0} sin (mathbf{1 0 0} boldsymbol{t}+boldsymbol{pi} / mathbf{3}) boldsymbol{m} boldsymbol{A} )
receptively. The power dissipated in the circuit is:
A ( cdot 10^{4} W )
в. ( 10 W )
c. ( 2.5 W )
D. ( 5.0 W )
12
348 An ( L C R ) circuit has ( L=10 m H, R= )
( 150 Omega ) and ( C=1 mu F ) connected in
series to a source of ( 150 sqrt{2} ) cos ( omega t ) volt.
At a frequency that is ( 50 % ) of the resonant frequency, calculate the average power (in ( boldsymbol{w} boldsymbol{a} boldsymbol{t} boldsymbol{t} ) ) dissipated per
cycle.
12
349 For an ( L-R ) circuit, the inductive
reactance is equal to the resistance ( boldsymbol{R} )
of the circuit. An emf ( boldsymbol{E}=boldsymbol{E}_{0} cos (boldsymbol{w} boldsymbol{t}) ) is
applied to the circuit. Then, the power consumed in the circuit is :
A ( cdot frac{E_{0}}{R} )
в. ( frac{E_{0}^{2}}{4 R} )
c. ( frac{4 R}{E_{0}} )
D. ( frac{R}{E_{0}} )
12
350 In LC oscillation resistance is ( 100 Omega ) and
inductance and capacitance is ( 1 mathrm{H} ) and
10 ( mu F ). Find the half power of frequency.
( mathbf{A} cdot 266.2 )
B. 366.2
c. 166.2
D. 233.2
12
351 In the given circuit find out :
(i) maximum value of current in the
circuit,
(ii) root mean square value of current in
the circuit,
12
352 In L-C-R circuit power of 3 mH
inductance and ( 4 Omega ) resistance, EMF
( boldsymbol{E}=mathbf{4} cos mathbf{1 0 0 0} boldsymbol{t} ) volt is applied. The
amplitude of current is
A ( .0 .8 AA )
в. ( frac{4}{7} )
c. ( 1.0 dot{A} )
D. ( frac{4}{sqrt{7}} dot{A} )
12
353 An arc lamp requires a direct current of ( 10 A ) at ( 80 mathrm{V} ) to function. If it is connected to a ( 220 mathrm{V}(mathrm{rms}), 50 mathrm{Hz} ) AC supply, the series inductor needed for it to work is
close to:
A . 80H
B. 0.08H
c. 0.0444
D. 0.065H
12
354 ( ln operatorname{an} L C R ) circuit as shown in figure,
both switches are open initially. Now
switch ( S_{1} ) is closed, ( S_{2} ) kept open. ( (q ) is
charge on the capacitor and ( 4 tau=R C ) is
capacity time constant).
Which of the following statement is
correct?
A ( cdot operatorname{At} t=frac{tau}{2}, q=C Vleft(1-e^{-1}right. )
B. Work done by the battery is half of the energy dissipated in the resistor
c. At ( t=tau, q=C V / 2 )
D. At ( t=2 tau . q=C Vleft(1-e^{-2}right) )
12
355 6. An A.C. is given by equation I=1, cos Ot+I sin ot. The
r.m.s. value of current is given by
(d) 1} +1
12
356 Give two point of difference between a step-up transformer and a step-down transformer? 12
357 If the reactance of a choke coil is ( X_{L} )
and its resistance is ( R ) then
A. ( X_{L}=R )
в. ( X_{L}>>R )
c. ( x_{L}<<R )
D. ( X_{L}=alpha )
12
358 In the A.C. circuit shown, keeping’ ( boldsymbol{K} )
pressed, if an iron rod is inserted into
the coil, the bulb in the circuit
A. Gets damaged
B. Glows less brightly
c. Glows with same brightness (as before the rod is inserted
D. Glows more brightly
12
359 In a series LCR circuit connected to an
a.c. source of voltage ( boldsymbol{v}=boldsymbol{v}_{m} sin omega boldsymbol{t} )
use phasor diagram to derive an expression for the current in the circuit. Hence, obtain the expression for the power dissipated in the circuit. Show that power dissipated at resonance is maximum.
12
360 Q Type your question
capacitor is ( 6 m F ) and is decreasing at
the constant rate ( 0.5 m F s^{-1} . ) The
potential difference across the
capacitor at the shown moment is changing as follows ( frac{boldsymbol{d} boldsymbol{V}}{boldsymbol{d} boldsymbol{t}}=boldsymbol{2} boldsymbol{V} boldsymbol{s}^{-1} )
( frac{boldsymbol{d}^{2} boldsymbol{V}}{boldsymbol{d t}^{2}}=frac{1}{2} boldsymbol{V} boldsymbol{s}^{-2} ) and the current in the
( 4 Omega ) resistor is decreasing at the rate of
( 1 m A s^{-1} . ) What is the potential
difference (in ( m V) ) across the inductor
at this moment?
( A cdot 4 )
B. 3
( c cdot 8 )
( D )
12
361 In series LCR circuit, the phase difference between applied voltage and current is
A. Positive when ( X_{L}>X_{C} )
B. Positive when ( X_{C}>X_{L} )
( c cdot 90^{circ} )
D. 0
12
362 In the circuit shown here, the ammeter
( A ) reads ( 5 A ) and the voltmeter ( V ) reads
20V.Find the correct value of resistance
12
363 Assertion
A step up transformer can also be used as a step down transformer
Reason
This is because ( frac{boldsymbol{E}_{boldsymbol{p}}}{boldsymbol{E}_{boldsymbol{s}}}=frac{boldsymbol{n}_{boldsymbol{s}}}{boldsymbol{n}_{boldsymbol{p}}} )
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Assertion is incorrect but Reason is correct
12
364 In an oscillating system, a restoring force is a must. In an ( L-C ) circuit,
restoring force is provide by
A. Capacitor
B. Inductance
c. Resistance
D. Both (A) and (B)
12
365 The reactance of a condenser of
capacity ( 50 mu mathrm{F} ) for an ( A C ) of frequency
( 2 times 10^{3} ) Hertz will be
( A .5 ) ohm
B. ( frac{2}{pi} )
( c cdot frac{3}{pi} )
D. ( frac{5}{pi} )
12
366 In an a.c. circuit, the instantaneous
e.m.f. and current are given by ( e= ) ( mathbf{1 0 0} sin mathbf{3 0} t, boldsymbol{i}=mathbf{2 0} sin left(mathbf{3 0} boldsymbol{t}-frac{boldsymbol{pi}}{mathbf{4}}right) . ) In one
cycle of a.c., the average power consumed by the circuit and the wattles current are, respectively.
A ( cdot frac{50}{sqrt{2}}, 0 )
в. 50,0
c. 50,10
D. ( frac{1000}{sqrt{2}}, 10 )
12
367 In a transformer, number of turns in primary and secondary are 500 and 2000 respectively. If current in primary is ( 48 mathrm{A} ), current in the secondary is :
( A cdot 144 A )
B. 24 A
( c cdot 48 A )
D. 12 A
12
368 In a series RLC circuit, the r.m.s. the
voltage across the resistor and the
inductor are respectively ( 400 mathrm{V} ) and
( 700 V . ) If the equation for the applied voltage is ( varepsilon=500 sqrt{2} sin omega t, ) then the
peak voltage across the capacitor is
B. ( 400 sqrt{2} V )
c. ( 400 V )
D. ( 1200 sqrt{2} mathrm{V} )
12
369 The frequency of the output signal becomes ( _{-}–_{-}-_{-}- ) times by doubling the value of the capacitance in the LC oscillator circuit.
A ( cdot sqrt{2} )
B. ( frac{1}{sqrt{2}} )
( c cdot frac{1}{2} )
D. 2
12
370 toppr 5
Q Type your question_
( mathbf{A} )
Reactance
( B )
Reactance
( c )
Reactance
D. Reactance
12
371 In a LR circuit of 3 m ( H ) inductane and
( 4 Omega ) resistance, emf ( E=4 cos (1000 t) )
volt is applied. The amplitude of current is:
( mathbf{A} cdot 0.8 A )
B. ( frac{4}{7} )
c. ( 1.0 A )
D. ( frac{4}{sqrt{7}} A )
12
372 A mixer of ( 100 Omega ) resistance is
connected to an A.C. source of ( 200 mathrm{V} ) and 50 cycles/sec. The value of average potential difference across the mixer will be:
( A cdot 308 V )
B. 264
c. 220
D. zero
12
373 In an L-C-R a.c. circuit at resonance, the
current:
A. is always in phase with the voltage
B. always leads the voltage
C . always lags behind the voltage
D. may lead or lag behind the voltage
12
374 47. In the above question, the capacitive reactance in the
circuit is
(a) 100 12
(b) 25 122
(c) V125 x 75 2 (d) 400
40 TL 1
tinha
12
375 A series LCR circuit with ( mathrm{R}=22 Omega, mathrm{L}=1.5 )
( mathrm{H} ) and ( mathrm{C}=40 mu mathrm{F} ) is connected to a variable frequency ( 220 mathrm{V} ) ac supply.
When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one
complete cycle?
A. 2000
B. 2200 W
c. 2400 ( w )
D. 2500 W
12
376 Assertion
Peak value of current in ( boldsymbol{A} boldsymbol{C} ) through a
resistance of ( 10 Omega ) is ( 2 A ). Then power
consumed by the resistance should be ( mathbf{2 0} boldsymbol{W} )
Reason
Power in ( boldsymbol{A C} ) is ( boldsymbol{P}=boldsymbol{I}_{r m s}^{2} boldsymbol{R} )
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
377 2.5
FuF capacitor and 3000-ohm resistance are joined in
TT
series to an ac source of 200 volt and 50 sec frequency.
The power factor of the circuit and the power dissipated
in it will respectively
(a) 0.6, 0.06 W
(b) 0.06, 0.6 W
(c) 0.6, 4.8 W
(d) 4.8, 0.6 W
12
378 The square root of the product
of inductance and capacitance has dimensions of
A . length
B. mass
( c . ) time
D. dimensionless
12
379 Let ( ell, r, c ) and ( v ) represent inductance, resistance, capacitance and voltage, respectively. The dimension of ( frac{ell}{r c v} ) is
SI units will be:
A. ( [L T A] )
B . ( left[L A^{-2}right] )
( mathbf{c} cdotleft[A^{-1}right] )
D cdot ( left[L T^{2}right] )
12
380 ( ln ) an oscillating ( L C ) circuit the
maximum charge on the capacitor is ( Q )
The charge on the capacitor when the energy is stored equally between the electric and magnetic field is
( mathbf{A} cdot Q / 2 )
в. ( Q / sqrt{3} )
c. ( Q / sqrt{2} )
D. ( Q )
12
381 (C) 2.0 X10S
(d) 2.5 x 10’s
18. An inductive coil has resistance of 100 12. When an ac
signal of frequency 1000 Hz is fed to the coil, the applied
voltage leads the current by 45°. What is the inductance
of the coil?
(a) 2 mH
(b) 3.3 mH
(c) 16 mH
(d) V5 mH
I
.
1
12
382 Assertion
The capacitive reactance limits the amplitude of the current in a purely capacitive circuit
Reason
Capacitive reactance is proportional to
the frequency and the capacitance
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
383 When the frequency of the AC voltage applied to series LCR circuit is gradually increased from a low value, the impedance of the circuit:
A. monotonically increases.
B. first increases and then decreases.
c. first decreases and then increases.
D. monotonically decreases
12
384 A ( 200 F ) capacitor is initially charged to ( 20 V ) and then shorted across a ( 5 m H )
inductor. The angular frequency of oscillation is
A. 1000 rad( / )s
B. 100 rad( / )s
c. 10000 rad( / )s
D. ( 1 r a d / s )
12
385 Figure shows a series LCR circuit
connected to a variable frequency 230 V
source. ( L=5.0 mathrm{H}, mathrm{C}=80 mu mathrm{F}, mathrm{R}=40 Omega )
(a) Determine the source frequency
which drives the circuit in resonance.
(b) Obtain the impedance of the circuit
and the amplitude of current at the
resonating frequency.
(c) Determine the rms potential drops
across the three elements of the circuit.
Show that the potential drop across the
LC combination is zero at the resonating
frequency.
12
386 Assertion: The resistance offered by an inductor in a d.c circuit is always
constant.
Reason : The resistance of inductor in
steady state is non-zero.
A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion.
B. If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion.
c. If Assertion is true statement but Reason is false
D. If both Assertion and Reason are false statements
12
387 An alternating voltage source is connected in an ( A C ) circuit whose
maximum value is 170 volt. The value
of potential at a phase angle of ( 45^{circ} ) will
be
A . 120.56 volt
B. 110.12 Volt
c. 240 volt
D. zero
12
388 A step up transformer is used to:
A. increase the current and increase the voltage
B. decrease the current and increase the voltage
C. increase the current and decrease the voltage
D. decrease the current and decrease the voltage
12
389 A transformer is used to light a 140 watt, 24 volt lamp from ( 240 V ) AC mains.
The current in the main cable is 0.7
amp. The efficiency of the transformer
is
A . ( 48 % )
B . ( 63.8 % )
c. ( 83.3 % )
D. 90%
12
390 In a transformer the output current and
voltage are ( 4 mathrm{A} ) and ( 20 mathrm{V} ) respectively. If the ratio of number of turns in the
primary and secondary coil is 2: 1 respectively, what is the input current and voltage?
( A cdot 2 A ) and 40
B. 1 A and 20
c. 4 A and ( 10 v )
D. 8 A and 40 v
12
391 Adjoining figure shows a series ( R C L ) circuit connected to an ac source which
generates an alternating emf of frequency ( 50 H z . ) The reading of the
voltmeters ( V_{1} ) and ( V_{2} ) are ( 80 V ) and ( 60 V )
respectively
Find:
The current in the circuit
12
392 A series LCR circuit with ( R=20 Omega, L=1.5 ) ( mathrm{H} ) and ( mathrm{C}=35 mu mathrm{F} ) is connected to a
variable-frequency ( 200 mathrm{V} ) ac supply. When the frequency of the supply equals the natural frequency of the circuit, what is the average power transferred to the circuit in one
complete cycle?
12
393 In a certain loaded transformer, the
secondary voltage is one-fourth the primary voltage. The secondary current is
A. one-fourth the primary current
B. four times the primary current
c. equal to the primary current
D. one-fourth the primary current and equal to the primary current
12
394 In series LCR circuit ( R=18 Omega ) and
impedance is ( 33 Omega ). An r.m.s. voltage
( 220 V ) is applied across the circuit. The true power consumed in a.c. circuit is
A . ( 200 W )
в. ( 400 mathrm{W} )
c. ( 600 W )
D. ( 800 W )
12
395 ( boldsymbol{I}=boldsymbol{6} cos boldsymbol{w} boldsymbol{t}+boldsymbol{8} sin boldsymbol{w} boldsymbol{t} ) is
applied across a resistor of ( 40 Omega ). Find the potential difference across
the resistor
A . ( 660 v )
B. 80
c. ( 330 v )
D. 400
12
396 An ( A C ) source rated ( 100 vee(r m s) )
supplies a current of ( 10 mathrm{A}(mathrm{rm} s) ) to a circiut. The average power delivered by the source. This question has multiple correct options
A. must be ( 1000 mathrm{w} )
B. may be ( 1000 mathrm{w} )
c. may be greater than 1000 w
D. may be less than 1000 w
12
397 The angular frequency for which he detects maximum current in the circuit
is
( mathbf{A} cdot 10^{5} / 7 r a d / s )
B . ( 10^{4} r a d / s )
c. ( 10^{5} r a d / s )
D. ( 10^{4} / 7 r a d / s )
12
398 A condenser and a ( 30 Omega ) resistance are
connected in series. When they are
connected to 120 V A.C. source then the
current flowing in the circuit is 1A The
p.d. across the ends of the condenser
will be nearly
( A cdot 1 v )
B. 116 ( v )
c. zero
D. 220
12
399 Find the current passing through battery immediately after key ( ( K ) ) is
closed. It is given that initially all the capacitors are uncharged (Given that ( R=6 Omega text { and } C=4 mu F) )
( A cdot 1 A )
( c .3 A )
0.24
12
400 An LCR series circuit with ( 100 Omega )
resistance is connected to an ac source
of ( 200 mathrm{V} ) and of frequency of ( 300 mathrm{rad} / mathrm{s} ) When only the capacitance is removed, the current lags behind the voltage by
( 60^{0} . ) When only the inductance is
removed, the current leads the voltage
by ( 60^{0} ) the current through the circuit is:
( A cdot 1 A )
B. 2 A
( c cdot 3 A )
D. ( 4 mathrm{A} )
12
401 Inductive resistance ( 25 Omega ) and
capacitive resistance ( 75 Omega ) are
connected across ( 250 V ) mains in
series. Find the rms potential difference across inductor and capacitor.
12
402 What is the coefficient of coupling for a
transformer in which ( 4 % ) of the total flux
generated in the primary does not pass through the secondary?
A . 0.4
B. 4
( c .9 .6 )
D. 0.96
12
403 7. The variation of the
instantaneous current (1)
and the instantaneous
emf (E) in a circuit is as o 702_ 3102
shown in figure Which of
the following statements
is correct?
(a) The voltage lags behind the current by rd2
(b) The voltage leads the current by ru2
(c) The voltage and the current are in phase
(d) The voltage leads the current by
12
404 The maximum current flowing long time after the switch ( mathrm{S} ) is moved to ( mathrm{B} )
should be
A. 0.707 A
B. 1.0 ( A )
( c cdot 0.5 mathrm{A} )
D. 1.414 A
12
405 A capacitor is connected to an A.C. circuit, then the phase difference between current and the voltage is :
A . ( pi )
в.
c. ( frac{-pi}{2} )
D. zero
12
406 Can the phenomenon of resonance be
exhibited in RL or RC circuit?
12
407 ( ln ) an ( A C ) circuit, the potential difference
( boldsymbol{V} ) and current ( boldsymbol{I} ) are given respectively by ( boldsymbol{V}=mathbf{1 0 0} sin (mathbf{1 0 0} boldsymbol{t}) boldsymbol{V} )
and ( boldsymbol{I}=mathbf{1 0 0} sin left(mathbf{1 0 0 t}+frac{boldsymbol{pi}}{mathbf{3}}right) boldsymbol{m} boldsymbol{A} )
The power dissipated in the circuit will be
A ( cdot 10^{4} K W )
в. ( 10 K W )
c. ( 2.5 K W )
D. ( 5 K W )
12
408 A power transmission line feeds input
power at ( 2400 mathrm{V} ) to a step down transformer with its primary winding having 4000 turns. What should be the
number of turns in the secondary winding in order to get output power at ( 240 vee ? )
A . 400
B. 420
( c cdot 424 )
D. 436
12
409 Find the amplitude response ( left|frac{V_{2}}{V_{1}}right| ) for
the circuit shown in figure. Determine
the half-power frequency.
A ( cdot frac{1}{R C} )
B. ( frac{sqrt{2}}{R C} )
( c cdot frac{sqrt{3}}{B C} )
D. ( frac{2}{R C} )
12
410 An inductor of reactance ( X_{L}=4 Omega ) and
resistor of resistance ( boldsymbol{R}=mathbf{3} Omega ) are
connected in series with a voltage
source of emf ( varepsilon= )
( (20 V)[sin (100 pi r a d / s) t] . ) The current in
the circuit at any time t will be?
A ( cdot I=(4 A)left[sin (100 pi r a d / s) t+37^{circ}right] )
B . ( I=(4 A)left[sin (100 pi r a d / s) t-37^{circ}right. )
C ( cdot I=(4 A)left[sin (100 pi r a d / s) t+53^{circ}right. )
D. ( I=(4 A)left[sin (100 pi r a d / s) t-53^{circ}right. )
12
411 In the following circuit the values of
( boldsymbol{L}, boldsymbol{C}, boldsymbol{R} ) and ( boldsymbol{E}_{mathbf{0}} ) are ( 0.01 mathrm{H}, mathbf{1 0}^{-mathbf{5}} boldsymbol{F}, mathbf{2 5 Omega} )
and 220 volt respectively. The value of current flowing in the circuit at ( boldsymbol{f}=mathbf{0} )
and ( boldsymbol{f}=infty ) will respectively be
( A cdot 8 A ) and ( 0 A )
B. ( 0 A ) and ( 0 A )
( c cdot 8 A ) and ( 8 A )
D. o ( A ) and ( 8 A )
12
412 The power loss is less in transmission lines, when :
A. Voltage is less but current is more
B. Both voltage and current are more
c. Voltage is more but current is less
D. Both voltage and current are less
12
413 16. For an RLC circuit driven with voltage of amplitude Vm
and frequency 0= true. The quality factor, Q is given
(6) WL
R
(d)
R
(0,0)
(JEE Main 2018)
12
414 An inductor, a resistor and a capacitor are joined in series with an AC source. As the frequency of the source is
slightly increased from a very low value, the reactance of the
A. inductor increases
B. resistor increases
c. capacitor increases
D. circuit increases
12
415 0000000
WWW
12. An inductor (L = 100 mH),
a resistor (R = 100 2),
and a battery (E = 100 V)
are initially connected
in series as shown in the
figure. After a long time
the battery is disconnected
after short circuiting the
points A and B. The current in the circuit 1 mm after the
short circuit is
(a) 0.1 A
(b) 1A
(c) A
(d) e A (AIEEE 2006)
12
416 A. ( C . ) supply gives ( 30 V ) r.m.s. which passes through a ( 10 Omega ) resistance. The power dissipated in it is :
B. ( 90 W )
c. ( 45 sqrt{2} mathrm{W} )
D. ( 45 W )
12
417 A capacitor of capacitance ( C ) has initial
charge ( Q_{0} ) and connected to an
inductance ( L . ) At ( t=0 ) switch ( S ) is
closed. The current through the inductor when energy in the capacitor is three times the energy of the inductor is :
A ( cdot frac{Q_{0}}{2 sqrt{L C}} )
в. ( frac{Q_{0}}{sqrt{L C}} )
c. ( frac{2 Q_{0}}{sqrt{L C}} )
D. ( frac{4 Q_{0}}{sqrt{L C}} )
12
418 An LC circuit contains a ( 40 mathrm{mH} ) inductor
and a ( 25 mu ) F capacitor. The resistance of the circuit is negligible. The time is measured from the instant the circuit
is closed. The energy stored in the circuit is completely magnetic at times (in milliseconds)
A . 0,3.14,6.28
B. 0, 1.57, 4.71
c. 1.57,4.71,7.85
D. 1.57, 3.14, 4.71
12
419 The output power in a step-up
transformer is
A. Greater than the input power
B. Equal to the input power
C. Maintained even during the power cut
D. Less than the input power
12
420 Name one source each of D.C and A.C. 12
421 In the given circuit initially the charge
on capacitor is ( Q_{0} ) At ( t=0 ) the switch ( S )
is closed Which of the following statement(s) is/are correct?
This question has multiple correct options
A . Maximum current through the inductor is ( frac{Q_{0}}{sqrt{L C}} )
B. charge on the capacitor is zero at ( t=frac{pi}{2} sqrt{L C} )
C. Current through the inductor is maximum at ( t= )
( frac{pi}{2} sqrt{L C} )
D. Maximum magnetic energy can be stored in the inductor is ( frac{Q_{0}^{2}}{2 C C} )
12
422 In a pure capacitive A.C circuit current and voltage differ in phase by
A ( cdot 0^{circ} )
B . ( 45^{circ} )
( mathrm{c} cdot 90^{circ} )
D. ( 180^{circ} )
12
423 Time
is closed at t = 0.
52. Switch S of the circuit shown in figure is closed at
If e denotes the induced
emf in L and i the current
flowing through the cir-
cuit at time 1, then which
of the following graphs
W
correctly represents the
2000-
variation of e with i?
12
424 A condenser of capacity ( 20 mu F ) is first charged and then discharged through a
10 ( m H ) inductance. Neglecting the
resistance of the coil, the frequency of the resulting vibrations will be
A. 356 cycle/s
B. 35.6 cycle/s
( mathbf{c} cdot 356 times 10^{3} ) cycle ( / mathrm{s} )
D. 3.56 cycle/s
12
425 The ( Q ) factor of a series LCR circuit with
( mathrm{L}=2 mathrm{H}, mathrm{C}=32 mu mathrm{F} ) and ( mathrm{R}=10 Omega mathrm{is} )
A . 15
B. 20
( c cdot 25 )
D. 30
12
426 Answer the following:
What is the impedance of a capacitor of capacitance ( C ) in an ( A C ) circuit using source of frequency n Hz?
12
427 29. For the circuit shown in the
figure, current in inductance is
0.8 A while that in capacitance is
0.6 A. What is the current drawn
from the source?
(a) 0.1 A
(b) 0.3 A
(c) 0.6 A
(d) 0.2 A
12
428 In a primary coil 5 A current is flowing on 220 volts. In a primary coil 5 A current is flowing on 220 volts. the ratio of number of turns in secondary coil and primary coil will be :
A .1: 10
B. 10:
( c cdot 1: 1 )
D. 11:
12
429 A condenser of ( 250 mu F ) is connected in
parallel to a cell of inductance ( 0.16 mathrm{mH} ) while its effective resistance is while
its. Determine the resonant frequency.
A ( cdot 9 times 10^{4} mathrm{Hz} )
B . ( 16 times 10^{7} ) Н ( _{2} )
c. ( 8 times 10^{5} ) Н ( z )
( mathbf{D} cdot 9 times 10^{3} mathrm{Hz} )
12
430 A series LCR circuit is connected to an
ac source. Using the phasor diagram, derive the expression for the impedance
of the circuit. Plot a graph to show the
variation of current with frequency of the source, explaining the nature of its variation.
12
431 An ideal coil of 10 H is connected in series with a
resistance of 5 12 and a battery of 5 V. Two seconds after
the connection is made, the current flowing (in A) in the
circuit is
(a) e
(b) e-
(d) 1 -e (AIEEE 2007)
To coaxial solenoids are mada ha
(C) 1–
12
432 In the given circuit (fig), all the symbols
have their usual meanings. At ( t=0, ) key
Kis closed. Now answer the following
questions. At ( t rightarrow infty, ) the equivalent
resistance between ( A ) and ( B ) is :
( mathbf{A} cdot R_{1}+R_{2}+R_{3} )
B. ( R_{1}+R_{2} )
( mathbf{c} cdot R_{1}+R_{3} )
D. None of the above
12
433 A coil has an inductance of ( 0.7 mathrm{H} ) and is
joined in series with a resistance of 220
Omega. When an alternating e.m.f. of ( 220 mathrm{V} ) at 50 c.p.s. is applied to it, then the wattless component of the current in the circuit is
A. 5 ampere
B. 0.5 ampere
c. 0.7 ampere
D. 7 ampere
12
434 In an A.C. circuit, the current flowing in
inductance is ( boldsymbol{I}=mathbf{5} sin (mathbf{1 0 0} boldsymbol{t}-boldsymbol{pi} / mathbf{2}) )
ampers and the potential difference is ( =200 sin (100 mathrm{t}) ) volts. The power
consumption is equal to
A. 1000 watt
B. 40 watt
c. 20 watt
D. zero
12
435 Assertion
An inductor coil normally produces
more current with ( D C ) source
compared to an ( A C ) source of same
value of rms voltage.
Reason
In ( D C ) source applied voltage remains
constant with time.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
436 ( A 5 mu F ) capacitor is connected to a 200 ( mathrm{V}, 100 mathrm{Hz} ) ac source. The capacitive
reactance is:
( mathbf{A} cdot 212 Omega )
B. ( 312 Omega )
c. ( 318 Omega )
D. ( 412 Omega )
12
437 In a series LCR circuit, what is the
phase difference between ( V_{L} ) and ( V_{C} )
where ( V_{L} ) is the potential difference
across the inductor and ( V_{C} ) is the potential difference across the capacitor?
12
438 A transformer has 100 turns in the
primary coil and carries 8 A current. If input power is ( 1 mathrm{kW} ), the number of turns
in secondary coil to have ( 500 vee ) output will be:
A ( cdot 100 )
B. 200
( c cdot 400 )
D. 300
12
439 In the series LCR circuit shown the
impedance is:
A. ( 200 Omega )
B. ( 100 Omega )
c. ( 300 Omega )
D. ( 500 Omega )
12
440 Transformer works on ( 220 V . ) Its
efficiency is ( 80 % ). Output power is ( 8 K W . ) Primary current is
approximately.
( mathbf{A} cdot 35 A )
в. ( 18 A )
( c .22 A )
D. ( 45 A )
12
441 An A.C. circuit containing only capacitance, the current:
A . Lags the voltage by ( 90^{circ} )
B . Leads the voltage by ( 90^{circ} )
c. Remains in phase with voltage
D. Lags the voltage by ( 180^{circ} )
12
442 An inductor ( 200 mathrm{mH} ), capacitor ( 500 mu mathrm{F} )
and resistor ( 10 Omega ) are connected in
series with a ( 100 mathrm{V} ) variable frequency ac source. What is the frequency at which the power factor of the circuit is unity?
A . ( 10.22 mathrm{Hz} )
B. 12.4 нz
c. ( 19.2 mathrm{Hz} )
D. 15.9 нz
12
443 What is meant by resonance in an LCR circuit? 12
444 A wire carrying ( 5.0 ~ V ) is applied to a
transformer. The primary coil has 5 turns and the secondary coil has 10 turns.
A . ( 0.50 V )
B. ( 5.0 V )
c. ( 10 V )
D. ( 50 V )
E . ( 100 V )
12
445 ( ln operatorname{an} mathrm{L}-mathrm{C} ) circuit ( boldsymbol{L}=mathbf{0 . 7 5} boldsymbol{H} ) and ( boldsymbol{C}= )
( 18 mu F . ) At the instant when the current
in the inductor is changing at a rate of ( 3.40 A / s, ) what is the charge on the capacitor?
A ( .45 .9 mu C )
B. ( 15.9 mu C C )
( c .55 .9 mu C )
D. ( 35.9 mu C )
12
446 In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit?
A. Only resistor
B. Resistor and inductor
c. Resistor and capacitor
D. Only inductor.
12
447 A ( 100 Omega ) resistor is connected to a
( 220 V, 50 H z A C ) supply. Find net power
consumed over a full cycle:
( mathbf{A} cdot 121 W )
B . ( 242 W )
c. ( 368 W )
D. ( 484 W )
12
448 A small signal voltage ( V(t)=V_{0} sin omega t )
is applied across an ideal capacitor ( boldsymbol{C} )
Then:
A . current ( I(t) ), lags voltage ( V(t) ) by ( 90^{circ} )
B. over a full cycle the capacitor ( C ) does not consume any energy from the voltage source
c. current ( I(t) ) is in phase with voltage ( V(t) )
D. current ( I(t) ) leads voltage ( V(t) ) by ( 180^{circ} )
12
449 Answer the following:
What is the value of impedance of a resonant series LCR circuit?
12
450 In an LCR circuit the capacitance is made ( frac{1}{4} ) then what should be the change in inductance that the circuit remains in resonance again?
( A cdot 8 ) times
B. ( frac{1}{4} ) times
( c cdot 2 ) times
D. 4 times
12
451 If the resistance in a parallel resonant circuit is reduced, the bandwidth:
A. increases
B. decreases
c. disappears
D. become sharper
12
452 Inductance ( L, ) capacitor ( C ) and resistor
( R ) are joined in series with an
alternating voltage source ( V=v_{0} sin omega t )
Find the formula of impedance and phase angle, drawing vector diagram of the circuit.
12
453 The ( Q ) factor of an ac circuit lies
between:
A. 0 and 1
B. – 1 and 1
c. -1 and 0
D. none of these
12
454 15. An arc lamp requires a direct current of 10 A at 80 V to
function. If it is connected to a 220 V (rms), 50 Hz AC
supply, the series inductor needed for it to work is close to
(a) 80 H
(b) 0.08 H
(c) 0.044 H
(d) 0.065 H (JEE Main 2016)
12
455 In a series LCR circuit ( mathrm{R}=4 Omega, mathrm{XL}=5 Omega ) and
( X_{C}=8 Omega, ) the current
A. leads the voltage by ( tan ^{-1}(3 / 4) )
B. leads the voltage by tan ( ^{-1}(5 / 8) )
C . leads the voltage by tan ( ^{-1}(3 / 5) )
D. leads the voltage by ( tan ^{-1}(5 / 9) )
12
456 An inductor may store energy in:
A. its electric field
B. its coils
C . its magnetic field
D. both in electric and magnetic fields
12
457 What is the range between ( f_{1} ) and ( f_{2} ) of
an RLC circuit that resonates at
( 150 k H z ) and has a ( Q ) of ( 30 ? )
A . ( 100.0 k H z ) to ( 155.0 k H z )
B. ( 147.5 k H z ) to ( 152.5 k H z )
c. ( 4500 k H z ) to ( 295.5 k H z )
D. ( 149970 H z ) to ( 150030 H z )
12
458 A transistor-oscillator using a resonant circuit with an inductor ( L ) (of negligible resistance) and a capacitor ( mathrm{C} ) in series produce oscillations of frequency f. If is doubled and ( C ) is changed to ( 4 C ), the frequency will be:-
( A cdot frac{f}{4} )
B. 8f
( c cdot frac{f}{2 sqrt{2}} )
( D cdot frac{f}{2} )
12
459 14. For the series LCR circuit shown in the figure, what is the
resonance frequency and the amplitude of the current
the resonating frequency
8 mH
mm
20 F
220 v ©
442
(a) 2500 rad-
sand 572 A
(b) 2500 rad-s- and 5 A
(C) 2500 rad-s’ and A
(d) 25 rad-s– and 572 A
12
460 11. A sinusoidal alternating current of peak value 10 passes
through a heater of resistance R. What is the mean power
output of the heater?
(a)
IOR
(6) LOR
(c) 21R
(d) 21R
12
461 Calculate inductive reactance of coil in
the following figure.
12
462 In a series resonant circuit, having L,C,R as its elements, the resonant current is
i. The power dissipated in the circuit at
resonance is
( mathbf{A} cdot i^{2} l omega )
B . ( i^{2} R )
c. zero
( mathbf{D} cdot i^{2} C omega )
12
463 If ( mathrm{N} ) is the number of turns in a coil, the value of self inductance varies as
A . ( N^{0} )
B.
c. ( N^{2} )
D. ( N^{-2} )
12
464 What is the average value of the AC voltage over one complete cycle?
A. zero
в. ( V_{max } )
c. ( frac{2 V_{max }}{pi} )
D. ( frac{V_{text {max }}}{2} )
12
465 e In the given circuit (figure), current through the 5 mH
inductor in steady state is
5 mH
M
نادرا مهدی
m
10 mH
20 V
522
win
را نیا
12
466 ( = )
( frac{1}{4} )
( = )
12
467 CARLOS
41.
34. The value of current in two series LCR circuits at resonance
is same. Then
(a) both circuits must be having same value of capacitance
and inductance
(b) in both circuits ratio of L and C will be same
(c) for both the circuits X[/Xc must be same at that fre-
quency
(d) both circuits must have same impedance at all frequencies
12
468 A resistor of ( 100 Omega ), a pure inductance coil of ( L=0.5 mathrm{H} ) and capacitor are in series in a circuit containing an a.c sources of ( 200 mathrm{V}, 50 mathrm{Hz} ). In the circuit, current is added is ahead of the voltage
by ( 30^{0} . ) Find the value of the capacitance
A . 1.46
B. 3
( c cdot 4 )
D. 5
12
469 An ( L-C-R ) series circuit with ( L= )
( 0.120 H, R=240 Omega, ) and ( C=7.30 mu F )
carries an rms current of ( 0.450 A ) with a
frequency of ( 400 H z . ) The average rate at
which electrical energy is converted to thermal energy in the resistor is given as ( frac{x}{10} W . ) Find ( x )
12
470 In series ( L-R ) circuit, ( X_{L}=R ). Now a
capacitor with ( X_{C}=R ) added in series.
New power factor:
A. Same as initial
B. ( frac{1}{sqrt{2}} ) times the initial
c. ( frac{1}{2} ) times the initial
D. ( sqrt{2} ) times the initial
12
471 The number of turns in the primary and secondary of a transformer are, respectively 100 and ( 50 . ) If the input power and input current are, respectively ( 60 mathrm{W} ) and ( 1 mathrm{A} ), and the efficiency of the transformer is
( 0.95, ) then, the output power and the output current will be, respectively
( A cdot 60 mathrm{W}, 2 mathrm{A} )
B. ( 60 mathrm{W}, 1 mathrm{A} )
c. ( 57 mathrm{w} ), 2 ( mathrm{A} )
D. 57 W, 1.9 A
12
472 24. An inductor and a resistor are connected in series with an
ac source. In this circuit.
(a) the current and the PD across the resistance lead the
PD across the inductance
(b) the current and the PD across the resistance lag behind
the PD across the inductance by an angle 7/2
(c) the current and the PD across the resistance lag behind
the PD across the inductance by an angle it
(d) the PD across the resistance lags behind the PD across
the inductance by an angle rc/2 but the current in
resistance leads the PD across the inductance by 7/2
12
473 An L-C-R circuit contains ( boldsymbol{R}=mathbf{5 0 Omega} )
( boldsymbol{L}=mathbf{1} boldsymbol{m} boldsymbol{H} ) and ( boldsymbol{C}=mathbf{0 . 1} boldsymbol{mu} boldsymbol{F} . ) The
impedence of the circuit will be minimum for a frequency of
( ^{mathbf{A}} cdot frac{10^{5}}{2 pi} H z )
в. ( frac{10^{6}}{2 pi} H z )
c. ( 2 pi times 10^{5} H z )
D. ( 2 pi times 10^{6} H z )
12
474 A step up transformer is connected on
the primary side to a rechargeable battery which can deliver a large current. If a bulb is connected in the
secondary, then
A. the bulb will glow very bright
B. the bulb will get fused
c. the bulb will glow, but with less brightness
D. the bulb will not glow
12
475 If ( V=100 sin 100 t ) volt, and ( I= )
( 100 sin left(100 t+frac{pi}{6}right) A . ) then find the watt
less power in watt?
A ( cdot 10^{text {। }} cdot 100 )
в. ( 10^{3} )
( c cdot 10^{2} )
D. ( 2.5 times 10^{3} sqrt{3} )
12
476 The values of ( L, C ) and ( R ) in an ( L-C- )
( R ) series circuit are ( 4 m H, 40 p F ) and
100 ( Omega ) respectively. The quality factor of the current is
A . 10
B. 100
( c cdot 1000 )
D. 10,000
12
477 ( ln ) an A.C circuit, the resistance ( boldsymbol{R}= )
( 0.2 Omega . ) At a certain instant, ( V_{A}-V_{B}= )
( 0.5 V, I=0.5 A, ) and the current is
increasing at the rate of ( frac{Delta I}{Delta t}=8 A / s ) The inductance of the coil is:
A . ( 0.05 H )
в. ( 0.1 mathrm{H} )
( c .0 .2 H )
D. none of these
12
478 A source of ( 220 mathrm{V} ) is applied in an ( mathrm{A} . mathrm{C} ) circuit. The value of resistance is ( 220 Omega )
Frequency ( & ) inductance are ( 50 mathrm{Hz} ) and
0.7 H, then wattless current is
A . ( 0.5 a m p )
в. ( 0.7 a m p )
c. ( 1.0 a m p )
( D cdot ) none
12
479 6. A group of electric lamps having a total power rating of
1000 watt is supplied by an ac voltage
E = 200 sin(310t + 60°).
Then the rms value o the circuit current is
(a) 10 A
(b) 10/2 A
(c) 20 A
(d) 2012 A
12
480 To measure
This question has multiple correct options
A. you will measure the potential drop across resistor till it is minimum on varying frequency
B. you will measure the voltage across ( L ) and ( C ) at various frequencies until ( V_{L}=V_{D} )
C. you will measure the voltage across L and C at various frequencies until ( V_{L}=V_{C} )
D. you will measure voltage across L until is minimum at a particular frequency
12
481 Ratio of impedance to capacitive
reactance has
A . no units
B. ohm
c. ampere
D. tesla
12
482 In a primary coil ( 5 A ) current is flowing
on 220 volts. If the secondary coil produces ( 2200 V ) voltage. Then the
ratio of number of turns in secondary coil and primary coil will be
( mathbf{A} cdot 1: 10 )
B. 10: 1
c. 1: 1
D. 11: 1
12
483 ( ln operatorname{an} L-C-R ) circuit the
capacitance is changed from ( C ) to ( 4 C )
For the same resonant frequency, the inductance should be changed from ( boldsymbol{L} )
to
A . L/4
B. L/2
c. 2L
D. 4L
12
484 The phase difference between alternating emf and current in a purely capacitive circuit will be
A . zero
в. ( pi )
( c cdot-frac{pi}{2} )
D.
12
485 The circuit shown in Fig. acts as a
A. tuned filter
B. low pass filter
c. high pass filter
D. rectifier
12
486 The primary and secondary coils of a transformer have 50 and 1500 turns
respectively. If the magnetic flux ( phi ) linked with the primary coil is given by ( phi=phi_{0}+4 t, ) where ( phi ) is in weber, t is
time in seconds and ( phi_{0} ) is a constant.
The output voltage across the secondary coil is
A ( .90 V )
( V )
в. ( 6000 V )
c. ( 220 V )
D. 30 ( V )
12
487 An ( L-C ) circuit consists of a ( 20.0 m H )
inductor and a ( 0.5 mu F ) capacitor. If the
maximum instantaneous current is
( 0.1 A, ) what is the greatest potential difference (in volts) across the
capacitor?
12
488 A step-down transformer increases the input current ( 4 A ) to 24 A at the secondary. If the, number of turns in the
primary coil is ( 330, ) the number of turns in the secondary coil is
A . 60
B. 50
( c cdot 65 )
D. 45
E. 55
12
489 Alternating voltage ( V=400 sin (500 Omega t) )
is applied across the resistance
( (0.2 K Omega) . ) The r.m.s value of current in
ampere is
( A cdot 1.414 mathrm{A} )
B. 14.14 A
( c cdot 0.1414 mathrm{A} )
( D cdot 2 A )
12
490 Assertion
In series ( L C R ) circuit if a ferromagnetic
rod is inserted inside an inductor,
current in the circuit may be increase
or decrease
Reason
By doing so ( X_{L} ) will increase.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
491 In the series LCR circuit (figure), the
voltmeter and ammeter readings are:
A. ( V=100 V, I=2 A )
B. ( V=100 V, I=5 A )
( mathbf{c} . V=1000 V, I=2 A )
D. ( V=300 V, I=1 A )
12
492 Assertion
At some given instant ( I_{1} ) and ( I_{2} ) both are
( mathbf{2} boldsymbol{A} ) each. Then ( boldsymbol{I} ) at this instant should
be zero.
Reason
There is a phase difference of ( pi ) between
( I_{1} ) and ( I_{2} ) functions
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
493 In a circuit, the current lags behind the voltage by a phase difference of ( pi / 2 ) the circuit will contain which of the
following:
A . Only R
B. Only c
c. ( R ) and ( c )
D. only L
12
494 A coil has resistance ( 30 Omega ) and inductive
reactance ( 20 Omega ) at ( 50 H z ) frequency.If an
ac source of ( 200 V, 100 H z ) is connected
across the coil, the current in the coil in
the coil will be
A ( cdot frac{20}{sqrt{13}} A )
в. ( 2.0 A )
c. ( 4.0 A )
D. ( 8.0 A )
12
495 A transformer connected to 220 volt line
shows an output of ( 2 A ) at ( 11000 V . ) The
efficiency is ( 100 % ). The current drawn from the line is:
( mathbf{A} cdot 100 A )
в. ( 200 A )
( c .22 A )
D. ( 11 A )
12
496 The value of admittance at resonance in
antiresonant
A ( cdot sqrt{G^{2}-S^{2}} )
B . ( G^{2}+S^{2} )
c. ( sqrt{G^{2}+S^{2}} )
D. ( frac{G^{2}}{S^{2}} )
12
497 A transformer lowers emf from ( 220 V ) to
( 12 V ) If the number of turns in primary
coil is 8800 , how many turns are there in the secondary coil?
A . 200
B. 300
( c cdot 480 )
D. 500
12
498 A current of 5 A is flowing at 220 V in the primary coil of a transformer. if the voltage produced in the secondary coil
is ( 2200 mathrm{V} ) anf ( 50 % ) of power is lost, then the current in secondary will be
12
499 While comparing the L-C oscillations with the oscillations of spring block system, with whom the magnetic energy can be compared and why? 12
500 The self inductance of a choke coil is
mH. when it is connected with a 10 VDC
source then the loss of power is 20 watt.
When it connected with 10 volt ( A C )
source loss of power is 10 watt. The frequency of AC source will bw-
( A cdot 50 mathrm{Hz} )
B. 60 Н
c. 80 н
D. 100 нz
12
501 The current in resistance ( mathrm{R} ) at
resonance in ac circuit is
A . zero
B. minimum but finite
c. maximum but finite
D. infinite
12
502 The reading of voltmeter and ammeter
in the following figure will respectively
be :
( A cdot O ) and ( 2 A )
B. 2A and OV
c. ( 2 v ) and ( 2 A )
D. ov and on
12
503 A resistance of ( 20 Omega ) is connected to a
source of alternating current rated ( 110 V, 50 H z ) Find the ( r m s ) current
12
504 The ( p . d . V ) across and current ( I ) flowing
through an instrument in an ( a . c . ) circuit
are given by ( V=2 cos omega t V ) and ( I= )
( 2 sin omega t A . ) The power dissipated in the
instrument is:
( mathbf{A} cdot 0 W )
B . ( 2.5 W )
c. ( 1.5 W )
D. ( 9 ~ W )
12
505 In the following circuit, the potential of
source is ( boldsymbol{E}_{mathbf{0}}=mathbf{2 0 0} ) volts, ( boldsymbol{R}=mathbf{2 0 0 Omega} )
( boldsymbol{L}=mathbf{0 . 1} ) henry, ( boldsymbol{C}=mathbf{1 0 . 6} ) farad and
frequency is variable, then the current
at ( f=0 ) and ( f=infty ) is :
A. ( 0 A, 10 A )
B. 10A, OA
C. ( 10 A, ) 10A
D. OA, OA
12
506 The phase angle between current and voltage in a purely inductive circuit is :
A . zero
в. ( pi )
( c cdot pi / 4 )
D. ( pi / 2 )
12
507 A step down transformer changes the
high input voltage used in our houses ( (120 V) ) into the low voltage used to charge an electric razor ( (24 V) . ) What must be the ratio of the turns of wire
from the primary side of the transformer to the secondary side?
A . 1: 5
в. 2: 7
( c cdot 1: 8 )
D. 2: 9
E .1: 10
12
508 A transformer consists of a coil of 1200
turns and another coil, with a total of
120 turns, which can be tapped at various places. Primary voltage is ( 240 V . ) At which pair of terminals would
you connect to a ( 12 V, 24 W ) lamp for it
to be lit normally?
A. ( N_{s}=60 )
is ( N_{s}=60 )
В. ( N_{s}=40 )
( mathbf{C} cdot N_{s}=80 )
D. ( N_{s}=50 )
12
509 An AC source of angular frequency ( omega ) is
fed across a resistor ( r ) and a capacitor
( C ) in series. The current registered is ( I ) If now the frequency of source is changed to ( omega / 3 ) (but maintaining the same voltage), the current in the circuit is found to be halved. Calculate the ratio
of reactance to resistance at the
original frequency ( omega )
A ( cdot sqrt{frac{3}{5}} )
B. ( sqrt{frac{2}{5}} )
c. ( sqrt{frac{1}{5}} )
D. ( sqrt{frac{4}{5}} )
12
510 Two different coils have self inductance
( boldsymbol{L}_{1}=mathbf{8} boldsymbol{m} boldsymbol{H} ) and ( boldsymbol{L}_{2}=boldsymbol{2 m} boldsymbol{H} . ) The
currents in both are increasing at the
same constant rate. At a certain instant
of time, the power given to the two coils
is the same. At this moment the
current, the induced voltage and energy
stored in the first coil are ( i_{1}, V_{1} ) and ( U_{1} )
respectively. The corresponding values
in the second coil are ( i_{2}, V_{2} ) and ( U_{2} ) respectively. Then the values of ( frac{i_{1}}{i_{2}}, frac{V_{1}}{V_{2}} ) and ( frac{boldsymbol{U}_{1}}{boldsymbol{U}_{2}} ) are respectively:
A ( cdot frac{1}{4}, 4, frac{1}{4} )
в. ( 4, frac{1}{4}, frac{1}{4} )
c. ( frac{1}{4}, frac{1}{4}, 4 )
D. ( _{4,4, frac{1}{4}} )
12
511 An RLC circuit has ( f_{1} ) and ( f_{2} ) as the half
power frequency and ( f_{0} ) as the resonant frequency. The Q factor of the circuit is given by:
A ( cdot frac{f_{1}+f_{2}}{2 f_{0}} )
в. ( frac{f_{1}-f_{0}}{f_{2}-f_{0}} )
c. ( frac{f_{0}}{f_{1}-f_{2}} )
D. ( frac{f_{1}-f_{2}}{f_{0}} )
12
512 58. In a black box of unknown elements
(L or R or any other combination),
an ac voltage E = E, sin (@t + ) is
applied and current in the circuit was
found to be I=1, sin [@t+0+ (Tc/4)].
Then the unknown elements in the
box may be
(a) only capacitor
(b) inductor and resistor both
(c) either capacitor, resistor, and inductor or only
capacitor and resistor
(d) only resistor
12
513 When the turns ratio of a step-up transformer is 20 and the primary ac voltage is ( 12 V ), the secondary voltage is
A . ( 12 V )
B. ( 120 V )
c. ( 240 V )
D. 2, 400V
12
514 79. In the circuit shown, sliding
contact is moving with uniform
velocity towards right. Its
value at some instance is 12 12.
The current in the circuit at
0000000
this instant of time will be
(a) 0.5 A
(b) more than 0.5 A
(c) less than 0.5 A
(d) may be less or more than 0.5 A depending on the value
• of L
12
515 At resonant frequency the current
amplitude in series LCR circuit is:
A. maximum
B. minimum
c. zero
D. infinity
12
516 A sinusoidal voltage ( V=200 sin 314 t ) is
applied to a ( 10 Omega ) resistor. Find the peak
voltage
( mathbf{A} cdot 200 V )
B. ( 400 mathrm{V} )
( mathbf{c} .600 V )
D. ( 800 mathrm{V} )
12
517 What is the phase difference between
AC e.m.f and current in the following? Pure resistor and pure inductor.
12
518 Vol112
3. The voltage time (V-t) + V.
graph for triangular wave
having peak value. Vo is
/4
as shown in figure. The – V.
average value of voltage Vin time interval from t = 0 to
Tis
(a) o
(6)
(d) none of these
12
519 According to the law of conservation of energy, any load impedance connected to the ideal transformer’s secondary
winding results in conservation of
A. reactive power
B. real
c. apparent
D. All of the above
12
520 In ( A C ) circuits choke is preferred to
resistors because
A. choke coil is cheap
B. voltage increase
c. energy is not wasted.
D. current increases
12
521 In a circuit inductance ( L ) and
capacitance ( C ) are connected as shown
in figure. ( A_{1} ) and ( A_{2} ) are ammeters

When key ( K ) is pressed to complete the
circuit, then just after closing key ( (boldsymbol{K}) )
the readings of ( A_{1} ) and ( A_{2} ) will be
A. zero in both ( A_{1} ) and ( A_{2} )
B. maximum in both ( A_{1} ) and ( A_{2} )
C. zero in ( A_{1} ) and maximum in ( A_{2} )
D. maximum in ( A_{1} ) and zero in ( A_{2} )

12
522 The power loss in an AC circuit can be minimized by.
A. Decreasing resistance and increasing inductance
B. Decreasing inductance and increasimg resistance
c. Increasing both inductance and resistance
D. Decreasing both inductance and resistance
12
523 In an alternating circuit applied voltage
is ( 220 V . ) If ( R=8 Omega, X_{L}=X_{C}=6 Omega )
then write the values of the following:
(a) Root mean square value of voltage.
(b) Impedance of circuit.
12
524 In an a.c. circuit, the instantaneous
e.m.f. and current are given by
( e=100 sin 30 t )
( i=20 sin left(30 t-frac{pi}{4}right) )
In one cycle of a.c., the average power consumed by the circuit and the wattless current are, respectively:
( mathbf{A} cdot 50,10 )
B. ( frac{1000}{sqrt{2}}, 10 )
c. ( frac{50}{sqrt{2}}, 0 )
D. 50,0
12
525 An rms voltage of ( 110 mathrm{V} ) is applied across a series circuit having a resistance ( 11 Omega ) and an impedance
( 22 Omega . ) The power consumed is
A ( .275 ~ W )
в. ( 366 mathrm{W} )
( c .550 W )
D. ( 1100 W )
12
526 The ac generator in the Figure supplies
( 150 V_{(max )} ) at ( 50 mathrm{Hz} . ) With the switch open as shown in the diagram, the
resulting current leads the generator
emf by ( 60^{circ} . ) With the switch in position
1, the current lags the generator emf by
( 30^{circ} . ) When the switch is in
position ( 2, ) the maximum current is ( 3 A )
Then, the value of R is:
A. ( 50 / sqrt{3} Omega )
B. 83.3 ( Omega )
c. ( 133.3 Omega )
D. ( 50 Omega )
12
527 In the AC circuit shown, ( X_{L}=7 Omega, R= )
( 4 Omega ) and ( X_{c}=4 Omega . ) The reading of the
ideal voltmeter ( V_{2} ) is ( 8 sqrt{2} ). The reading
of the ideal ammeter will be:
A . ( 1 A )
в. ( 2 A )
c. ( sqrt{2} A )
D. ( frac{1}{sqrt{2}} )
12
528 resistance leaus wie D DTU33 uit llluuulance by
25. Figure shows a source of alter-nating voltage conne
to a cap-acitor and a resistor.
Which of the following phasor
diagrams correctly describes the
phase relationship between Ic, the
current between the source and the
capacitor, and Ir, the current in the
resistor?
Ic
IR
(c)
CR
(d)
12
529 ( 200 V ) A.C is applied at the ends of an LCR circuit. The circuit consists of an
inductive reactance ( boldsymbol{X}_{boldsymbol{L}}=mathbf{5 0 Omega} )
capacitive reactance ( X_{C}=50 Omega ) and ohmic resistance ( R=10 Omega ). Calculate
the impedance of the circuit and also
potential difference across ( L ) and ( R )
What will be the potential difference
across L-C?
12
530 ge in
when
and
11. A coil of inductance 300 mH and resistance 2
is connected to a source of voltage 2 V. The current
reaches half of its steady state value in
(a) 0.3 s
(b) 0.15 s
(c) 0.1 s
(d) 0.05 s (AIEEE 2005)
12
531 In an A.C circuit, a resistance R is
connected in series with an inductance
L. If the phase angle between voltage
and current be ( 45^{0}, ) the value of
inductive reactance will be
A ( cdot frac{R}{4} )
в. ( frac{R}{2} )
c. ( R )
D. ( frac{R}{3} )
12
532 In a transformer, in which the losses
may be neglected, the ratio of the primary voltage to secondary voltage is found to be ( 4: 1 . ) The ratio of the
primary to secondary turns and the ratio of the primary current to secondary current are respectively in
the ratio of :
( A cdot 4: 1 & 1: 4 )
B. ( 1: 4 & 4: 1 )
c. ( 4: 1 & 4: 1 )
D. ( 1: 4 & 1: 4 )
12
533 An emf of ( 15 V ) is applied in a circuit of inductance ( 5 H ) and resistance ( 10 Omega )
The ratio of currents flowing at ( t=infty )
and ( t=1 s ) will be
A ( cdot 1-e^{-1} )
B ( cdot e^{-1} )
c. ( frac{e^{2}}{e^{2}-1} )
D. ( frac{e^{1 / 2}}{e^{1 / 2}-1} )
12
534 In series combination of ( boldsymbol{R}, boldsymbol{L}, boldsymbol{C} ) with an
A.C source at resonanace, if ( boldsymbol{R}=mathbf{2 0} )
ohm, then impedence ( Z ) of the combination is
A. 20 ohm
B. zero
c. 10 ohm
D. 400 ohm
12
535 If the frequency of an alternating e.m.f.
is ( f ) in ( L-C-R ) circuit, then the value of
impedance ( mathbf{Z} ) as log(frequency)
increases:
A. increases
B. increases and then becomes equal to resistance, then it will start decreasing
c. decreases and when it becomes minimum, equal to the resistance then it will start increasing
D. go on decreasing
12
536 (0)
100
45. A resistor and an inductor are connected to an ac supply
of 120 V and 50 Hz. The current in the circuit is 3 A.
If the power consumed in the circuit is 108 W, then the
resistance in the circuit is
(a) 122
(b) 40 12
(c) (52 x 28) 2 (d) 360 12
12
537 A step-down transformer has a coil ratio of 1.5 to ( 17 . ) The voltage applied at the
primary side of the transformer is ( 136 V )
What is the output voltage of the transformer?
A . ( 1.2 V )
в. ( 1.5 V )
c. ( 5.25 V )
D. ( 12 V )
E . ( 18.75 V )
12
538 The instantaneous emf and current
equations of an RLC series circuit are ( e=200 sin left(omega t-frac{pi}{6}right) )
( i=20 sin left(omega t+frac{pi}{6}right) )
The average power consumed per cycle is
A. zero
в. ( 2000 mathrm{W} )
c. ( 1000 W )
D. ( 500 W )
12
539 Voltage across each elements of a
series LCR circuit are given by ( V_{L}= )
( mathbf{6 0} boldsymbol{V}, boldsymbol{V}_{boldsymbol{C}}=mathbf{2 0} boldsymbol{V}, boldsymbol{V}_{boldsymbol{R}}=mathbf{3 0} boldsymbol{V} ) Find out
source voltage
A . ( 50 v )
B. 100v
( c cdot 150 v )
D. 200v
12
540 Plot a graph showing variation of capacitive reactance with the change in the frequency of the ( A C ) source. 12
541 With increase in frequency of an ac
supply, the impedance of an ( L-C-R )
series circuit
A. remains constant
B. increases
C . decreases
D. decrease at first becomes minimum and then
increases.
12
542 The reactance of inductance at ( 10^{4} H z )
is ( 10^{4} Omega . ) Its reactance at ( 2 times 10^{4} H z ) will
be:
A ( cdot 10^{4} Omega )
B ( cdot 2 times 10^{4} Omega )
( mathbf{c} cdot 3 times 10^{4} Omega )
D. ( 4 times 10^{4} Omega )
12
543 For a series LCR circuit at resonance,
the statement which is not true is
A. Peak energy stored by a capacitor = peak energy stored by an inductor
B. Average power = apparent power
C. Wattless current is zero
D. Power factor is one
12
544 The maximum current in the inductor
is:
A ( cdot frac{3 V_{0}}{2} sqrt{frac{3 C}{L}} )
3. ( V_{0} sqrt{frac{3 C}{L}} )
( ^{c} cdot 2 V_{0} sqrt{frac{3 C}{L}} )
( v_{0} sqrt{frac{C}{I}} )
12
545 The primary winding of a transformer has 100 turns and its secondary winding has 200turns. The primary is connected to an A.C supply of ( 120 mathrm{V} ) and the current flowing in it is 10 A. The voltage and the current in the secondary
are
A. ( 240 V, 5 A )
в. ( 240 V, 10 A )
c. ( 60 V, 20 A )
D. ( 120 V, 20 A )
12
546 In above circuit, what is the potential
drop across ( Z Y ? )
A ( cdot 160 )
B. ( 80 sqrt{80} )
( c cdot 80 v )
( D )
12
547 In a circuit ( mathrm{L}, mathrm{C} ) and ( mathrm{R} ) are connected in
series with an alternating voltage source of frequency v. The current leads
the voltage by ( 45^{0} . ) The value of ( C ) is
A ( cdot frac{1}{pi v(2 pi v L-R)} )
B . ( frac{1}{2 pi v(2 pi u L-R)} )
c. ( frac{1}{pi v(2 pi v L+R)} )
D. ( frac{1}{2 pi v(2 pi v L+R)} )
12
548 Which of the following graphs represents the correct variation of
capacitive reactance ( boldsymbol{X}_{C} ) with
frequency ( nu ? )
( A )
B.
c.
D.
12
549 An inductor L of inductance ( boldsymbol{X}_{boldsymbol{L}} ) is
connected in series with a bulb ( mathrm{B} ) and
an ac source. How would brightness of the bulb change when (i) number of turn in the inductor is reduced, (ii) an
iron rod is inserted in the inductor and
(iii) a capacitor of reactance ( boldsymbol{X}_{boldsymbol{C}}=boldsymbol{X}_{boldsymbol{L}} )
is inserted in series in the circuit.
Justify your answer in each case.
12
550 The inductor in a LC oscillation has a
maximum potential difference of ( 16 mathrm{V} )
and maximum energy of ( 640 mu ) J. Find
the value of capacitor in ( mu ) F in LC circuit.
A. ( F=5 mu F )
В. ( F=6 mu F )
c. ( F=7 mu F )
D. ( F=8 mu F )
12
551 In the given circuit, the value of resistance effect of the coil Lis exactly
equal to the resistance R. Bulbs B1 and B2 are exactly identical. Answer the following question.
a) Which one of the two bulbs lights up earlier, when key k is closed and why?
b) What will be the comparative brightness of the two bulbs after sometime if the key ( mathrm{K} ) is kept closed
and why?
12
552 Assertion
Potential difference across, resistor,
capacitor and inductor each is ( 10 V ) Then, voltage function and current functions should be in phase.
Reason
At this condition current in the circuit
should be maximum.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
553 A transformers has an efficiency of ( 80 % )
.It is connected to a power output of kw and 100 V.If the secondary voltage is ( 240 mathrm{V} ),the secondary current is
A ( .4 .6 mathrm{A} )
B. 40 A
( c cdot 4.3 mathrm{A} )
D. 13.3 A
12
554 The value of resistance of the coil
calculated by the student is :
A . ( 3 Omega )
в. ( 4 Omega )
( c .5 Omega )
D. 8Omega
12
555 ( mathbf{A} mathbf{5 0} boldsymbol{W}, mathbf{1 0 0} boldsymbol{V} ) lamp is to be connected
to an ( A C ) mains of ( 200 V, 50 H z . ) What capacitance is essential to be put in series with the lamp?
A . 9.2
B. 8
c. 10
D. 12
12
556 11. When an ac source of e.m.f.e= E, sin(100t) is connected
across a circuit, the phase difference between the emf e
and the current i in the circuit is observed to be /4, as
shown in the diagram. If the circuit consists possibly only
of RC or LC in series, find the relationship between the
two elements
i ore
(a) R=1 k92,C = 10 uF (b) R= 1 k-2, C = 1 uF
(c) R = 1 k 2, L = 10 uH (d) R= 1 k 2, L = 1H
12
557 In an a.c. circuit, containing an inductance and a capacitor in series, the current is found to be maximum
when the value of inductance is
0.5henry and of capacitance is 8F. The
angular frequency of the input A.C. Voltage must be equal to
A. 0.5
B. 0.10
( c )
D. 0.3
12
558 When ( Q=200 mu C, ) what is the value of
I?
12
559 A ( 12 Omega ) resistor and a ( 0.21 H ) inductor
are connected in series to an a.c source
operating at ( 20 ~ V, 50 ) cycle/second.
The phase angle between current and source voltage is
A . ( 30^{circ} )
В . ( 40^{circ} )
( c cdot 80^{circ} )
D. ( 90^{circ} )
12
560 A power transmission line feeds input at ( 2200 mathrm{V} ) to a step-down transformer with its primary windings having 3000 turns. find the number of turns in the
secondary to get the power input at 220
( mathbf{V} )
12
561 An ac circuit consist of a series
combination of circuit elements ( X ) and
( Y . ) The Current is ahead of the voltage in phanse by ( frac{pi}{4} . ) If element ( X ) is a pure resistor of ( 100 Omega )
(a) name the circuit element ( Y )
(b) calculate the rms value of current, if
rms value of voltage is ( 141 V )
(c) what will happen if the ac source is replaced by a dc source?
12
562 Determine the power consumed in the
circuit in ( mathbf{w} )
12
563 An AC source is connected to a resistive
circuit. Which of the following is true?
A. Current leads ahead of voltage in phase
B. Current lags behind voltage in phase
c. current and voltage are in same phase
D. Any of the above may be true depending upon the value of resistance
12
564 When the values of inductance and
capacitance in an ( L-C ) circuit are
( 0.5 H ) and ( 8 mu F ) respectively then
current in the circuit is maximum. The
angular frequency of alternating e.m.f. applied in the circuit will be
A ( .5 times 10^{3} ) Radian/sec
B. 50 Radian/sec
c. ( 5 times 10^{2} ) Radian/sec
D. 5 Radian/sec
12
565 The reactance of a circuit is zero. It is
possible that the circuit contains This question has multiple correct options
A. an inductor and a capacitor
B. an inductor but no capacitor
c. a capacitor but no inductor
D. neither an inductor nor a capacitor
12
566 The quality factor of an AC circuit is related to bandwidth as
A. inversely proportional
B. directly proportional
c. directly proportional to log
D. inversely proportional to log
12
567 If the total charge stored in the LC
circuit is ( Q_{0}, ) then for ( t geq 0 )
A ( cdot ) the charge on the capacitor is ( mathrm{Q}=mathrm{Q}_{0} cos left(frac{pi}{2}+frac{mathrm{t}}{sqrt{mathrm{LC}}}right) )
B. the charge on the capacitor is ( mathrm{Q}=mathrm{Q}_{0} cos left(frac{pi}{2}-frac{mathrm{t}}{sqrt{mathrm{LC}}}right) )
c. the charge on the capacitor is ( Q=-L C frac{d^{2} Q}{d t^{2}} )
D. the charge on the capacitor is ( mathrm{Q}=-frac{1 mathrm{d}^{2} mathrm{Q}}{sqrt{mathrm{LC}} mathrm{d}^{2}} )
12
568 Figure shows a LCR circuit connected
with a dc battery of emf ( varepsilon ) and internal
resistance ( R ). Initially the capacitor was
uncharged. After a long time:
This question has multiple correct options
A ( cdot ) current through the inductor is ( frac{varepsilon}{8 R} )
B. charge stored in the capacitor is ( C frac{^{2}}{4} )
C. charge stored in the capacitor is ( C frac{e}{2} )
D. potential difference across the terminals of battery is
( frac{varepsilon}{4} )
12
569 In the series ( L C R ) circuit as shown in
figure, the voltmeter and ammeter
readings are:
A. ( V=100 ) volt, ( I=2 ) amp
B. ( V=100 ) volt, ( I=5 ) amp
c. ( V=1000 ) volt, ( I=2 ) amp
D. ( V=300 ) volt, ( I=1 ) amp
12
570 C, respectively, are connected in series with an inductor of inductance ( L )
Initially the capacitors have charge
such that ( V_{B}-V_{A}=4 V_{0} ) and ( V_{C}- )
( V_{D}=V_{0} . ) Initial current in the circuit is
zero. Find:
a. the maximum current that will flow in
the circuit.
b. the potential difference across each
capacitor at that instant.
( mathbf{A} cdot I_{0}=V_{0} sqrt{frac{3 C}{L}} ; mathbf{b} . V_{1}=3 V_{0}, V_{2}=3 V_{0} )
B ( cdot I_{0}=V_{0} sqrt{frac{6 C}{L}} ; ) b. ( V_{1}=3 V_{0}, V_{2}=3 V_{0} )
C ( cdot I_{0}=V_{0} sqrt{frac{3 C}{L}} ; ) b. ( V_{1}=1.5 V_{0}, V_{2}=3 V_{0} )
D ( cdot I_{0}=V_{0} sqrt{frac{6 C}{L}} ; ) b. ( V_{1}=1.5 V_{0}, V_{2}=3 V_{0} )
12
571 The correct relation between the
impedance of secondary coil with that of primary coil is
( mathbf{A} cdot Z_{S}=Z_{P} )
в. ( Z_{S}=Z_{P} frac{N_{S}}{N_{P}} )
( ^{mathrm{c}} Z_{S}=Z_{P}left(frac{N_{S}}{N_{P}}right)^{2} )
D. ( _{Z_{S}}=Z_{P}left(frac{N_{P}}{N_{S}}right)^{2} )
12
572 The instantaneous voltage through a device of impedence ( 20 Omega ) is ( e= )
( 80 sin 100 pi t . ) The effective value of the
current is
( A .3 A )
в. ( 2.828 A )
c. ( 1.732 A )
D. ( 4 A )
12
573 Which of the following graphs represents the correct variation of
inductive reactane ( X_{L} ) with frequency ( v )
7
( A )
в.
c.
D.
12
574 An electrical device draws 2 kW power
from ac mains voltage ( 223 V(r m s) ) The current differs lags in phase by ( phi=tan ^{-1}left(-frac{3}{4}right) ) as compared to
voltage. The resistance ( R ) in the circuit
is:
A . ( 15 Omega )
B. 20Omega
c. ( 25 Omega )
D. 30Omega
12
575 An inductor of ( 30 mathrm{mH} ) is connected to a
( 220 mathrm{V}, 100 mathrm{Hz} ) ac source. The inductive
reactance is then
A . ( 10.58 Omega )
в. ( 12.64 Omega )
c. ( 18.85 Omega )
D. 22.67Omega
12
576 46. A resistor and a capacitor are connected to an ac supply
of 200 V, 50 Hz in series. The current in the circuit is 2 A.
If the power consumed in the circuit is 100 W then the
resistance in the circuit is
(a) 100 12
(b) 252
(c) /125 x 75 2
(d) 400 22
12
577 A condenser of capacity ( C ) is charged to
a potential difference of ( V_{1} ). The planes
of the condenser are then connected to
an ideal inductor of inductance ( L ). The
current through the inductor when the
potential difference across the
condenser reduces to ( V_{2} ) is ?
A ( cdot frac{Cleft(V_{1}^{2}-V_{2}^{2}right)}{L} )
B. ( frac{Cleft(V_{1}^{2}+V_{2}^{2}right)}{L} )
( left(frac{Cleft(V_{1}^{2}-V_{2}^{2}right)}{L}right)^{1 / 2} )
( left(frac{Cleft(V_{1}-V_{2}right)^{2}}{L}right)^{1 / 2} )
12
578 A resistor and a capacitor are connected to an ac supply of ( 200 V, 50 H z ) in series. The current in the circuit is ( 2 A ). If the power consumed in the circuit is ( 100 W ) then
the resistance in the circuit is
( mathbf{A} cdot 100 Omega )
в. 25 ( Omega )
c. ( sqrt{125 times 75} Omega )
D. ( 400 Omega )
12
579 When a coil is connected to a ( 100 mathrm{V} ) DC
supply, the current is 2 A. When the
same coil is connected to AC source
( E=100 sqrt{2} sin omega t, ) the current is ( 1 A )
Find the inductive reactance used in
the circuit.
12
580 The output power in step-up transformer used in practice is
A. Greater than the input power
B. Equal to the input power
c. Less than the input power
D. None of the above
12
581 A leaky capacitor ( 10 Omega / 60^{circ} ) is
connected in series with a ( 10 Omega )
resistance. Find the overall impedance.
Fig. 26.42
A. ( 10 Omega )
B. ( 10 sqrt{2} ) ?
( mathrm{c} cdot 15 Omega )
D. ( 10 sqrt{3} Omega )
12
582 The potential difference between the
ends of a resistance ( mathrm{R} ) is ( V_{R}, ) between
the ends of capacitor is ( V_{C}=2 V_{R} ) and
between the ends of inductance is ( V_{L}= )
( 3 V_{R} ) then the alternating potential of
the source in terms of ( V_{R} ) will be:
A ( cdot sqrt{2} V_{R} )
в. ( V_{R} )
c. ( frac{V_{R}}{sqrt{2}} )
D. ( 5 V_{R} )
12
583 An alternating e.m.f. of ( 200 mathrm{V} ) and 50 cycles is connected to a circuit of
resistance ( 3.142 Omega ) and inductance
0.01H. The lag in time between the e.m.f. and the current is :
A . ( 1.5 mathrm{ms} )
B. 2.5 ms
c. 3.5ms
D. 0.5 ms
12
584 ( S_{1}: ) In an elastic collision initial and
final K.E. of system will be same.
( S_{2}: ) In a pure ( L-C ) Circuit average
energy stored in capacitor is zero. ( S_{3}: ln Y D S E ) coherent sources are formed by division of wave front method
( S_{4}: ) If a physical Quantity is quantized then it must be integral multiple of it’s lowest value.
A . FFTF
в. ( T T F T )
c. ( F T F T )
D. ( T F T F )
12
585 A step up transformer operates on a 230 volt line and supplies to a load of 2 amp. The ratio of primary to secondary windings is ( 1: 25 . ) Determine the primary
current
A. 12.5 amp
B. 50 amp
c. 8.8 amp
D. 25 amp
12
586 Current flowing in the circuit 12
587 A transformer with primary to secondary turns ratio of ( 1: 2, ) is connected to an alternator of voltage ( 200 mathrm{V} . ) A current of ( 4 mathrm{A} ) is flowing through the primary coil. Assuming that the transformer has no losses, the
secondary voltage and current are respectively:
( A cdot 100 vee, 8 A )
B. ( 400 vee, 8 A )
c. ( 400 vee, 2 mathrm{A} )
D. ( 100 vee, 2 A )
12
588 If ( E_{p} ) and ( E_{s} ) are the input and output voltages of a transformer, then:
(where ( n_{p} ) is the number of turns in
primary and ( n_{s} ) is the number of turns in secondary
A ( cdot frac{E_{s}}{E_{p}}=frac{n_{p}}{n_{s}} )
B . ( E_{s} E_{p}=n_{s} n_{p} )
c. ( E_{s} n_{p}=E_{p} n_{s} )
D. None of these
12
589 53. In the circuit shown in the figure,
if both the bulbs B, and B2 are
L = 10 mH
identical,
(a) their brightness will be the
same
220 V, 50 Hz
(b) B, will be brighter than B
(c) B, will be brighter than B2
(d) only B, will glow because the capacitor has infinite
impedance
12
590 A resistor ( R ) on inductance ( 0.2 H ) and a
capacitor of capacitance ( C ) are
connected in series. A sinusoidal
voltage of ( r m s ) value ( 200 V ) is applied across the combination using a fixed
frequency oscillator. If the rms value of current through the circuit is ( 2.828 A ) and the inductive and capacitive reactances are ( 3 R ) and ( 2 R ) respectively. Calculate (i) resistance of the resistance of the resistor
(ii) frequency of ( A C ) (iii) capacitance of the capacitor.
( begin{array}{ll}text { A. } & (500 Omega, 119.3 H z, 13.3 mu F)end{array} )
B. ( quad(50 Omega, 119.3 H z, 13.3 mu F) )
C. ( quad(50 Omega, 1193 H z, 133 mu F) )
D. ( quad(50 Omega, 0.1193 H z, 133 mu F) )
12
591 The transformation ratio in the step-up
transformer is
A .
B. Greater than one
c. Less than one
D. The ratio greater or less than one depends on the other factors
12
592 In the given circuit what is the potentia
drop across resistance?
A. ( 40 v )
B. 80
( c cdot 120 v )
D. zer
12
593 To step ( 110 V ) ac down to ( 20 V ) ac, the
turns ratio must be
A . 5.5
B . 18
c. 0.18
D. 0.018
12
594 An electrical heater and a capacitor are joined in series across a ( 220 V, 50 H z )
( A C ) supply. The
potential difference across the heater is
( 90 V . ) The potential difference across the
capacitor will be about
( mathbf{A} cdot 200 V )
B. ( 130 V )
( mathrm{c} cdot 110 mathrm{V} )
D. ( 90 V )
12
595 An ideal transformer is used on 220 V
line to deliver 2 A at 110 V. The current
through the primary is :
( A cdot 10 A )
B. 5 A
( c cdot 1 A )
D. 0.1 A
12
596 A step-up transformer of turns ratio 2
1 has ( 50 H z A C ) voltage applied to
primary. The frequency of ( A C ) output
voltage across secondary is
A. zero
B. ( 25 H z )
( mathbf{c} .50 H z )
D. ( 100 H z )
12
597 Primary coil of a step-up transformer
has number of turns than
secondary coil.
A. more
B. less
c. same
D. cant say
12
598 An alternating current of ( 1.5 m A ) and
angular frequency 300 rad/sec flows
through a ( 10 K Omega ) resistor and a ( 0.50 mu F ) capacitor in series. find the rms voltage across the capacitor and impedance of the circuit?
A ( cdot 1.2 times 10^{4} Omega ; 10 V )
B . ( 10^{4} Omega ; 10^{4} V )
c. ( 1.0 times 1.0^{4} Omega ; 50 V )
D. ( 10 Omega ; 10 v )
12
599 If a circuit made up of a resistance ( 1 Omega ) and inductance ( 0.01 mathrm{H}, ) and alternating emf ( 200 mathrm{V} ) at ( 50 mathrm{H} ) is connected, then
the phase difference between the
current and the emf in the circuit is :
12
600 In an ideal transformer, the voltage is stepped down from 11KV to 220V. If the primary current be 20 A the current in
the secondary should be
A. 5 k ( A )
B. 1 kA
c. ( 0.5 mathrm{kA} )
D. 0.1 kA
12
601 A resistance ( (R=12 Omega), ) an inductor
( boldsymbol{L}=mathbf{2} boldsymbol{H}) ) and a capacitor ( (boldsymbol{C}=mathbf{5} boldsymbol{mu} boldsymbol{F}) )
are connected to an AC generator of
frequency ( 50 H z . ) Which of the following statement is correct?
A. At resonance, the circuit impedance is zero
B. At resonance, the circuit impedance is ( 12 Omega )
c. At resonance, the frequency of the circuit is ( 1 / 2 pi )
D. The inductive reactance is less than the capacitive reactance
12
602 The self inductance of a coil is ( 1 / 2 ) henry.
At what frequency will its inductive
reactance be ( 3140 Omega )
A ( .100 H z )
B. ( 10 H z )
c. ( 1000 H z )
D. ( 10000 H z )
12
603 A light bulb is rated at ( 100 W ) for a
( 220 V ) supply. Find the resistance of the
bulb:
A . ( 184 Omega )
B. ( 284 Omega )
c. ( 384 Omega )
D. ( 484 Omega )
12
604 The inductive reactance of a choke coil
of ( 1 / 4 pi m H ) in an ( A C ) circuit of ( 50 H z ) will be
A. 25 ohm
B. 0.25 ohm
c. 0.025 ohm
D. 2.5 ohm
12
605 10. Two alternating voltage generators produce emfs of the
same amplitude E, but with a phase difference of 73. The
resultant emf is
(a) Esin[ax + (7/3)] (b) E, sin[or+ (1/6)
(c) V3 E, sin[et + (rt/6)] (d) V3 E, sin[or+ (1/2)]
11
12
606 Derive an expression for impedence and
current in the series ( L C R ) circuit using phasor diagram
12
607 What is meant by rms (effective) value
of alternating current?
12
608 A transformer steps up an AC supply from ( 220 mathrm{V} ) to ( 2200 mathrm{V} ). If the secondary coil of the transformer has 2000 turns,
the number of turns in its primary coil will be :
A . 200
B. 100
( c .50 )
D. 20
12
609 In a series LCR circuit connected to an
ac source of variable frequency and voltage ( boldsymbol{v}=boldsymbol{v}_{m} sin omega boldsymbol{t}, ) draw a plot
showing the variation of current (I) with angular frequency ( ( omega ) ) for two different values of resistance ( boldsymbol{R}_{1} ) and ( boldsymbol{R}_{2}left(boldsymbol{R}_{1}>right. )
( left.R_{2}right), ) Write the condition under which
the phenomenon of resonance occurs. For which value of the resistance out of
the two curves a sharper resonance is produced? Define ( Q ) -factor of the circuit and give its significance
12
610 A transformer with a ( 110 V ) primary has
a 15: 1 turns ratio. The load resistance,
( R_{L}, ) is ( 120 . ) What is the approximate voltage across the load?
A . ( 7.3 V )
B. ( 73 V )
( c .88 V )
D. ( 880 V )
12
611 20
E alllla
(AIEEE 2007)
16. An inductor of inductance
L = 400 mH and resistors of
resistances R1 = 2 ohm and R =
2 2 are connected to a battery
of emf 12 V as shown in the
figure. The internal resistance
of the battery is negligible. The
switch S is closed at t = 0. The potential drop across L as
a function of time is
(a) be stv
(b) 1 2 3
(c) 6(1 – e-t/0.2) V (d) 12e-51 V (AIEEE 2009)
12
612 A transformer has an efficiency of ( 80 % ) It works at ( 4 mathrm{kW} ) and ( 100 mathrm{V} ). If the
secondary voltage is ( 240 mathrm{V} ), the current in primary coil is
( mathbf{A} cdot 0.4 mathrm{A} )
B. 4 A
c. 10 А
D. 40 A
12
613 63. In the adjoining ac circuit the voltmeter whose reading
will be zero at resonance is
mw
(a) Vi
(c) V₃
(b) V2
(d) V4
12
614 An alternating e.m.f. of ( boldsymbol{E}= ) ( 100 sin (100 pi t) ) is connected to a choke of negligible resistance and current oscillations of amplitude 1 A
are produced. The inductance of the choke should be
( mathbf{A} cdot 100 H )
в. ( frac{1}{pi} H )
c. ( 1 H )
D. ( pi H )
12
615 ( A 220 V, 50 H z A C ) generator is connected to an inductor and a ( 50 Omega ) resistance in series. The current in the
circuit is ( 1.0 A . ) What is the Potential
difference across inductor?
A. ( 102.2 V )
в. ( 186.4 mathrm{V} )
c. ( 214 V )
D. ( 170 V )
12
616 How can you improve the quality factor of a parallel resonance circuit. Obtain the resonant frequency and quality factor of a series L-C-R
circuit with ( L=4 mathrm{H}, mathrm{C}=64 mu F ) and ( mathrm{R}= )
( 20 Omega )
12
617 (9) TOU
(d) 60°
40. In an ac circuit, V and I are given by
V= 100 sin (100 t) volts, I = 100 sin
wa
mA. The
power dissipated in circuit is
(a) 104 watt
(b) 10 watt
(c) 2.5 watt
(d) 5 watt
12
618 ( ln ) a parallel ( L-C-R ) circuit as
shown in figure if ( I_{R}, I_{L}, I_{C} ) and ( I )
represents the rms values of current
flowing through resistor, inductor, capacitor and the source, then choose the appropriate correct answer
( mathbf{A} cdot I=I_{R}+I_{L}+I_{C} )
В . ( I=I_{R}+I_{L}-I_{C} )
c. ( I_{L} ) or ( I_{C} ) may be greater than ( I )
D. None of the above
12
619 The ( Q ) – factor of a resonant circuit is
equal to
( ^{mathbf{A}} cdot frac{1}{L} sqrt{frac{R}{C}} )
в. ( frac{1}{R} sqrt{frac{L}{C}} )
c. ( frac{1}{R L} sqrt{C} )
D. ( frac{1}{C} sqrt{frac{R}{L}} )
12
620 The current in the coil decreases from
10 Amp to 5 Amp in 0.1 second.. Calculate the co-efficient of self-
inductance if induced e.m.f. is ( 5 mathrm{V} )
12
621 A generator at a utility company produces ( 100 A ) of current at ( 4000 V )
The voltage is stepped up to ( 240000 V ) by a transformer before it is sent on a high voltage transmission line. The current in transmission line is
A ( .3 .67 A )
в. ( 2.67 A )
c. ( 1.67 A )
D. ( 2.40 A )
12
622 A ( 10 Omega ) resistance, ( 5 m H ) coil and ( 10 mu F )
capacitor are joined in series. When a suitable frequency alternating current source is joined to this combination, the circuit resonates. If the resistance
is halved, the resonance frequency:
( A ). is halved
B. is doubled
c. remains unchanged
D. is quadrupled
12
623 In a purely inductive circuit, the
current:
A. is in phase with the voltage
B. is out of phase with the voltage
C . leads the voltage by ( pi / 2 )
D. lags behind the voltage by ( pi / 2 )
12
624 In the adjoining circuit, calculate the inductive reactance and the capacitive
reactance. What should be the source
frequency so that the two reactance become equal in magnitude? What would then be the impedance(in ohms) of the circuit?
12
625 The net resistance of the circuit at
resonance is
( ^{A} cdot frac{mathrm{L}}{mathrm{CR}} )
в. ( R )
( c cdot frac{mathrm{CR}^{3}}{mathrm{L}} )
D ( frac{mathrm{L}^{2}}{mathrm{C}^{2} mathrm{R}^{3}} )
12
626 A transformer is used to light a ( 120 W ) ( 24 V ) lamp from ( 240 V ) a.c. mains. The
current in the main cable is ( 0.6 A . ) The efficiency of the transformer is
A . ( 48 % )
B. ( 63.8 % )
c. ( 83.3 % )
D. ( 90 % )
12
627 CISL
UTIV
68. For the given circuit as summing inductor and source to
be ideal, the phase difference between currents I, and l.is
m
12
628 A series ( L C R ) circuit has an inductance
of ( 100 m H, ) a capacitor ( 0.1 mu F ) and a
resistance of ( 200 Omega ). Find the impedance
at resonance and the resonant
frequency.
12
629 The turn ratio of a transformer is ( 2: 3 . ) If
the current through primary is ( 3 A ), then current through load resistance is
( A cdot 1 A )
B. 4.5 A
( c cdot 2 A )
D. 1.5 A
12
630 Calculate the total reactance if two
inductor of ( 10 mathrm{mH} ) and ( 50 mathrm{mH} ) are
connected in series with ( 10 mathrm{kHz} ) AC.
12
631 n the transformer shown in figure, the
load resistor is ( 50 Omega ). The turns ratio
( N_{1}: N_{2} ) is 10: 2 and the source voltage
is ( 200 mathrm{V}(mathrm{r} . mathrm{m} . mathrm{s}) . ) If a voltmeter across the
load measures ( 25 mathrm{V} ) (r.m.s.), then the
source resistance ( R_{S} ) is (power loss is
negligible)
( A cdot 450 Omega )
в. ( 750 Omega )
c. ( 2000 Omega )
D. 100Omega
12
632 In a series L.C.R circuit, the potential drop across ( L, C ) and ( R ) respectively are ( 40 V, 120 V ) and ( 60 V . ) Then the source
voltage is
( mathbf{A} cdot 220 V )
B. ( 160 V )
( mathbf{c} cdot 180 V )
D. ( 100 V )
12
633 An ( L C ) circuit contains a 20 m ( H )
inductor and a ( 50 mu F ) capacitor with an
initial charge of 10 mC.The resistance
of the circuit is negligible. Let the instant circuit is closed be at ( t=0 )
What is the total energy stored initial? Is it conserved during the ( L C ) oscillations?
A. ( 0.01 mathrm{J} ), yes
B. ( 0.1 mathrm{J} ), yes
c. 1 J, yes
D. 2 J, yes
12
634 The value of current in two series ( L C R )
circuits at resonance is same. Then
A. both circuits must be having same value of capacitance and inductance
B. in both circuits ratio of ( L ) and ( C ) will be same
c. for both the circuits ( X_{L} / X_{C} ) must be same at that frequency
D. both circuits must have same impedance at all frequencies
12
635 The natural frequency of the circuit shown in fig. is
A ( frac{1}{sqrt{L C}} )
B. ( frac{1}{2 sqrt{L C}} )
c. ( frac{2}{sqrt{L C}} )
D. none of these
12
636 If the rms current through a ( 6.8 k Omega )
resistor is ( 8 m A ), the rms voltage drop
across the resistor is
( mathbf{A} cdot 5.44 V )
в. ( 54.4 mathrm{V} )
c. ( 7.07 V )
D. 8V
12
637 A series LCR circuit contains
inductance ( 5 m H, ) capacitance ( 2 mu F ) and resistance ( 10 Omega ). If a frequency A.C. source is varied, what is the frequency at which maximum power is dissipated?
( ^{mathbf{A}} cdot frac{10^{5}}{pi} H z )
в. ( frac{10^{-5}}{pi} H z )
c. ( frac{2}{pi} times 10^{5} H z )
D. ( frac{5}{pi} times 10^{3} H z )
12
638 The amount of power delivered by the
AC source in the capacitor ( & ) resistance
( R_{1} ) of the circuit given above is ( frac{X}{8} times 10^{3} )
watt. Then x is:
12
639 ( ln a R, L, C ) circuit, three elements is
connected in series by an a.c. source. If frequency is less than resonating frequency then net impedance of the circuit will be
A. capacitive
B. inductive
c. capacitive or inductive
D. pure resistive
12
640 The input AC voltage to the transformer
is ( 3 mathrm{kV} ) and output is ( 100 mathrm{V} ). Then:
A. The ratio of number of turns in the primary to secondary coil is 30: 1
B. The transformer is a step down transformer
c. The transformer is a step up transformert
D. Both 1 and 2
12
641 A series resonant circuit contains ( boldsymbol{L}= ) ( frac{5}{pi} m H, C=frac{200}{pi} mu F ) and ( R=100 mu ). If a
source of emf ( e=200 sin 1000 pi t ) is
applied, then the rms current is:
A ( .2 A )
в. ( 200 sqrt{2} A )
D. ( 1.41 A )
12
642 In an a.c., circuit with phase voltage ( boldsymbol{V} )
and current ( I ), the power dissipated is
( ^{A} cdot frac{V I}{2} )
B. ( frac{V I}{sqrt{2}} )
c. ( V I )
D. VIcostheta
12
643 The effective resistance in between the
points A and B in the circuit given is?
12
644 The primary to secondary turns ratio of a transformer is given as ( 2: 3 . ) If the current through the primary coil is ( 3 A ) then the current through load resistance is
( A cdot 1 A )
в. 4.5 А
( c cdot 2 A )
D. 1.5 A
12
645 22. In the series LCR circuit (see figure), the voltmeter and
ammeter readings are:
400 V 400 V
R = 50 S2 L
100 V, 50 Hz
(a) V= 100 V, I = 2 A
(c) V = 1000 V, I= 2 A
(b) V= 100 V, 1 = 5 A
(d) V= 300 V, I = 1 A
12
646 A resistor ( R, ) inductor ( L ) and a capacitor ( mathrm{C} ) are connected in series to an
oscillator of frequency v. If the resonant
frequency is ( boldsymbol{v}_{r}, ) then the current lags behind the voltage, when:
( mathbf{A} cdot v=0 )
В. ( vv_{r} )
D. ( v=v_{r} )
12
647 A transformer consists of 500 turn in
the primary coil and 10 turns in a
secondary coil with the load of ( 10 Omega ) Find out current in the primary coil when the voltage across the secondary
coil is ( mathbf{5 0} boldsymbol{V} )
A . ( 5 A )
в. ( 1 A )
( c cdot 10 A )
D. ( 2 A )
12
648 17. A resistance of 20 2 is connected to a source of an alter-
nating potential V = 220 sin(100 g). The time taken by
the current to change from the peak value to rms value, is
(a) 0.2 s
(b) 0.25 s
(c) 2.5 x 10-s (d) 2.5 x 10-s
12
649 A coil of ( 10^{-2} H ) inductance carries a
current ( boldsymbol{I}=2 sin (mathbf{1 0 0} boldsymbol{t}) boldsymbol{A} . ) When current
is half of its peak value then at that instant the induced emf in coil :-
A . ( 1 V )
B. ( sqrt{2} V )
c. ( sqrt{3} V )
D. 2
12
650 Potential difference across capacitor of
capacitance ( C ) when the current in the
circuit is maximum is:
a. ( frac{V_{0}}{4} )
в. ( frac{3 V_{0}}{4} )
( c cdot frac{5 V_{0}}{4} )
D. none of these
12
651 The figure shows the graphical
variation of the reactance of a capacitor
with frequency of ac source.

Draw the graph showing the variation of
the reactance of this inductor with
frequency.

12
652 ( ln L-C ) oscillations
This question has multiple correct options
A ( cdot ) time period of oscillations is ( frac{2 pi}{sqrt{L C}} )
B. maximum current is ( frac{q_{0}}{sqrt{L C}} )
C. maximum rate of change of current in circuit is ( frac{q_{0}}{L C} )
D. maximum potential difference across the inductor is
( frac{q_{0}}{2 C} . ) Here ( q_{0} ) is maximum charge on capacitor.
12
653 A sinusoidal voltage of peak value ( 283 V ) and angular frequency ( 320 / s ) is applied to a series LCR circuit. Given
that ( boldsymbol{R}=mathbf{5} boldsymbol{Omega}, boldsymbol{L}=mathbf{2 5} boldsymbol{m} boldsymbol{H} ) and ( boldsymbol{C}= )
1000 ( mu F ). The total impedance, and
phase difference between the voltage
across the source and the current will
respectively be:
( mathbf{A} cdot 7 Omega ) and ( 45^{circ} )
B. ( 10 Omega ) and ( tan ^{-1}left(frac{5}{3}right) )
c. ( 10 Omega ) and ( tan ^{-1}left(frac{8}{3}right) )
D. ( 7 Omega ) and ( tan ^{-1}left(frac{5}{3}right) )
12
654 The resonance point in ( boldsymbol{X}_{L}-boldsymbol{f} ) and
( X_{c}-f ) curve is
( r )
12
655 In an oscillating LC circuit the maximum charge on the capacitor is ( Q ) The charge on the capacitor when the energy is stored equally between the electric and magnetic field is:
A ( cdot frac{Q}{3} )
в. ( frac{Q}{sqrt{3}} )
c. ( frac{Q}{sqrt{2}} )
D.
12
656 ( ln ) an ac circuit, the resistance of ( mathrm{R} Omega ) is connected in series with an inductance
I. If phase angle between voltage and
current be ( 45^{circ}, ) the value of inductive
reactance will be:
A. ( R / 2 )
B. ( R / sqrt{2} )
( c . R )
D. Insufficient data
12
657 Define capacitor reactance. Write its S.I.
units
12
658 An alternating voltage given as ( boldsymbol{V}= ) ( mathbf{1 0 0} sqrt{mathbf{2}} sin 100 t quad ) is applied to a
capacitor of ( 1 mu F ). The current reading of
the ammeter will be equal to ( mathrm{mA} )
A . 10
B . 20
c. 40
D. 80
12
659 An alternating emf given by equation ( boldsymbol{E}=mathbf{3 0 0} sin [(mathbf{1 0 0} boldsymbol{pi}) boldsymbol{t}] ) volt is applied to
a resistance 100 ohms. The rms current
through the circuit is (in amperes):
( ^{A} cdot frac{3}{sqrt{2}} )
в. ( frac{9}{sqrt{2}} )
( c cdot 3 )
D. ( frac{6}{sqrt{2}} )
12
660 un
connected in the circuit as shown in fig.
Initially capacitor A has no charge and
capacitor ( mathrm{B} ) has ( mathrm{CV} ) charge. Assume that
the circuit has no resistance at all. At
( t=0, ) switch ( S ) is closed, then ( [ ) given ( boldsymbol{L} boldsymbol{C}=frac{boldsymbol{2}}{boldsymbol{pi}^{2} times mathbf{1 0}^{4}} boldsymbol{s}^{2} ) and ( boldsymbol{C V}=mathbf{1 0 0 m C} )
This question has multiple correct options
A. when current in the circuit is maximum, charge on each capacitor is same
B. when current in the circuit is maximum, charge on capacitor A is twice the charge on capacitor
C ( . q=50(1+cos 100 pi t) m C, ) where ( q ) is the charge on
capacitor B at time t
D. ( q=50(1-cos 100 pi t) m C ), where q is the charge on
capacitor B at time t
12
661 The primary winding of transformer has 500 turns whereas its secondary has ( mathbf{5 0 0 0} ) turns. The primary is connected to an A.C supply of ( 20 V, 50 H z ). The secondary will have an output of
A. ( 2 V, 5 H z )
в. ( 200 V, 500 H z )
( mathbf{c} cdot 2 V, 50 H z )
D. ( 200 V, 50 H z )
12
662 In an A.C. circuit, the instantaneous
values of e.m.f. and current are ( boldsymbol{E}= )
( 200 sin 314 t ) volts and ( I=sin (314 t+ )
( pi / 3) ) ampere then the average power
consumed in watts is
A . 200
B. 100
( c cdot 0 )
D. 50
12
663 If in an A.C., L-C series circuit ( boldsymbol{X}_{c}>boldsymbol{X}_{boldsymbol{L}} )
Hence potential
A. Lags behind the current by ( pi / 2 )
B. Leads the current by ( pi ) in phase
c. Leads the current by ( pi / 2 ) in phase
D. Lags behind the current by ( pi ) in phase
12
664 & In the circuit shown in figure neglecting source resistance
the voltmeter and ammeter reading will respectively, will be
R=300X2= 252
X=259
240 V
(a) OV, 3 A
(c) 150 V, 6 A
(b) 150 V, 3A
(d) OV,8A
12
665 For an LCR circuit, the power transferred
from the driving source to the driven
oscillator is ( boldsymbol{P}=boldsymbol{I}^{2} boldsymbol{Z} ) cos ( boldsymbol{p} ) Then
A. the power factor ( cos phi>0, P>0 )
B. the driving force can give no energy to the oscillator (P ( =0 ) ) in some cases.
C. the driving force cannot syphon Out (P ( <0 ) ) the energy out of oscillator.
D. all of these.
12
666 An inductor ( 200 m H, ) capacitor ( 500 mu F )
resistor ( 10 Omega ) are connected in series
with a ( 100 V ), variable frequency ac
source.
Calculate:
(i) frequency at which power factor of circuit its unity
(ii) current amplitude at this frequency
(iii) Q-factor.
12
667 If the current in a primary coil of transformer decreases from ( 0.8 mathrm{A} ) to 0.2
( A ) in 4 millisecond, then calculate induced emf in the secondary coil
[Coefficient of mutual induction is 1.76
( mathrm{H}] )
12
668 33. For the circuit shown in the figure, the ammeter A, reads
1.6 A and ammeter Az reads 0.4 A. Then
(a) 0= TIC
(b) f= TIC
(c) the ammeter A, reads
1.2 A
(d) the ammeter A, reads 2 A
12
669 When the frequency of the voltage applied to a series RC circuit is increased, the phase angle
A . increases
B. decreases
c. remains the same
D. becomes erratic
12
670 Assertion
A given transformer can be used to
step-up or step-down the voltage
Reason
The output voltage depends upon the
ratio of the number of turns of the two
coils of the transformer
A. Both Assertion and Reason are correct and Reason is
the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is
not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
671 A transformer steps up an ac supply from 220 to 2200 V. If the secondary coil of the transformer has 2000 turns, Then
find the number of turns in its primary coil :
( mathbf{A} cdot N_{p}=250 ) turns
B. ( N_{p}=300 ) turns
C ( . N_{p}=100 ) turns
D. ( N_{p}=200 ) turns
12
672 A current ( i_{0} ) is flowing through an ( L-R )
circuit of time constant ( t_{0} . ) The source
of the current is switched off at time
( boldsymbol{t}=mathbf{0} . ) Let ( boldsymbol{r} ) be the value of ( (-boldsymbol{d i} / boldsymbol{d} boldsymbol{t}) ) at
time ( t=0 . ) Assuming this rate to be
constant, the current will reduce to zero
in a time interval of:
A ( cdot t_{0} )
B . ( e t_{0} )
( c cdot t_{0} / e )
D. ( left(1-frac{1}{e}right) t_{0} )
12
673 A ( 5 c m ) long solenoid having 10 ohm
resistance and ( 5 m H ) inductance is
joined to a ( 10 V ) battery. At steady state, the current through the solenoid (in ampere) will be
( mathbf{A} cdot mathbf{5} )
B . 2
( c . )
D. zero
12
674 Assertion
A capacitor blocks the direct current in
the steady state.
Reason
The capacitive reactance of the capacitor is inversely proportional to
frequency ( f ) of the source of emf.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
675 In the circuit shown, a ( 30 mathrm{V} ) d.c source
gives a current ( 2.0 mathrm{A} ) as recorded in the
ammeter ( A ) and ( 30 V ) a.c. source of
frequency ( 100 mathrm{Hz} ) gives a current ( 1.2 mathrm{A} )
The inductive reactance is
( A cdot ) 10ohm
B. 20 ohm
( mathbf{c} cdot 5 sqrt{34} ) ohm
D. 40 ohm
12
676 The sum of rms potential difference across each of the three elements is
A . 50 volt
B. ( 50 sqrt{2} ) volt
c. ( frac{50}{sqrt{2}} ) volt
D. None of these
12
677 A transformer has 200 turns in primary and 400 turns in secondary. When a battery of ( 6 mathrm{V} ) and negligible internal resistance is connected to the primary a current of ( 2 mathrm{A} ) is produced in it. The secondary voltage and current are
( A cdot 12 v, 1 A )
B. 12 V, zero
c. zero, 1A
D. zero, zero
12
678 An inductance, a capacitance and a resistance are connected in series
across a source of alternating voltages. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of
A . ( pi / 4 )
B. zero
( c )
D. ( pi / 2 )
12
679 Assertion: In series LCR circuit
resonance can take place.
Reason: Resonance takes place if inductance and capacitive reactances are equal and opposite.
A. If both assertion and reason are true but the reason is the correct explanation of assertion.
B. If both assertion and reason are true but the reason is not the correct explanation of assertion
c. If assertion is true but reason is false
D. If both the assertion and reason are false
E. If reason is true but assertion is false
12
680 Assertion
( ln operatorname{an} A C ) circuit potential difference
across the inductor may be greater than the applied voltage.
Reason
( boldsymbol{V}_{C}=boldsymbol{I} boldsymbol{X}_{C}, ) whereas ( boldsymbol{V}=boldsymbol{I} boldsymbol{Z} ) and ( boldsymbol{X}_{boldsymbol{C}} )
can be greater than ( Z ) also.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
681 Quality factor of series resonance circuit is given by
A ( cdot frac{f_{2}-f_{1}}{f_{0}} )
в. ( f_{2}-f_{1} )
c. ( frac{f_{1}-f_{0}}{f_{2}} )
D. ( frac{f_{0}}{f_{2}-f_{1}} )
12
682 With increase in frequency of an AC supply, the impedence of an L-C-R series circuit
A. remains constant
B. increases
c. decreases
D. decreases at first, becomes minimum and then increases
12
683 Assertion
The inductive reactance limits
amplitude of the current in a purely inductive circuit
Reason
The inductive reactance is independent
of the frequency of the current
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
684 59. In an ideal transformer, the voltage and the current in the
primary coil are 200 V and 2 A, respectively. If the voltage
in the secondary coil is 2000 V, then the value of current
in the secondary coil will be
(a) 0.2 A
(b) 2 A
(c) 10 A
(d) 20 A
12
685 2
39. What will be the phase difference between virtual voltage
and virtual current, when the current in the circuit is
wattless?
(a) 90°
(b) 45°
(c) 180°
(d) 60°
12
686 An alternating voltage of 260 volt and ( omega ) ( =100 ) radian/second, is applied in an
LCR
series circuit where ( mathrm{L}=0.01 mathrm{H}, mathrm{C}=4 times )
( 10^{-4} F ) and ( R=10 Omega . ) the power supplied
by the source is:
A. 1000 w
в. 6760 w
( c . ) 3380 ( w )
D. 3000
12
687 What do you mean by electrical
resonance? An LC circuit is in a
condition of resonance. If ( C=1.0 times 10^{-6} )
( F ) and ( L=0.25 H, ) then find the frequency
of oscillation of the circuit.
12
688 An oscillator circuit contains an
inductor ( 0.05 H ) and a capacitor
of capacity ( 80 mu F ).When the maximum
voltage across the capacitor is ( 200 V ) the maximum current (in amperes) in the circuit is
( A cdot 2 )
B. 4
c. 8
D. 10
E. 16
12
689 The natural frequency of a ( L-C ) circuit
is
A ( cdot frac{1}{2 pi sqrt{L C}} )
в. ( frac{1}{2 pi} sqrt{frac{C}{L}} )
c. ( frac{1}{2 pi} sqrt{frac{L}{C}} )
D. ( sqrt{L C} )
12
690 ( frac{-}{k} ) 12
691 The phase difference between alternating emf and current in a purely capacitive circuit will be
A . zero
в. ( pi )
( c cdot-frac{pi}{2} )
D.
12
692 Which of the following combination should be selected for better turning of an L.C.R circuit used for
communication?
A. ( R=25 Omega, L=1 cdot 5 H, C=45 mu F )
в. ( R=25 Omega, L=1 cdot 5 H, C=35 mu F )
c. ( R=25 Omega, L=2 cdot 5 H, C=45 mu F )
12
693 In ( P-f ) curve the half power
frequencies are those at which
A ( cdot P=frac{P_{max }}{sqrt{2}} )
B. ( P=frac{P_{text {max }}}{2} )
c. ( quad P=frac{P_{max }}{4} )
D. ( P=P_{max } )
12
694 An alternating voltage ( boldsymbol{V}=boldsymbol{V}_{0} sin (boldsymbol{omega} boldsymbol{t}) )
is applied across a circuit. As a result, a
current ( boldsymbol{I}=boldsymbol{I}_{0} sin (boldsymbol{omega} boldsymbol{t}-boldsymbol{pi} / 2) ) flows in it
The power consumed per cycle is
A . zero
в. ( 0.5 V_{0} I_{0} )
c. ( 0.707 V_{0} I_{0} )
D. ( 1.414 mathrm{V}_{0} mathrm{I}_{0} )
12
695 (U) Lei
62. The reading of ammeter in the circuit shown will be
r.
x c=50
0
110v
X = 522
R= 552
(a) 2 A
(2) 2 A
(c) Zero
(b) 2.4 A
(d) 1.7 A
12
696 In a Zener regulated power supply a
Zener diode with ( V_{z}=6.0 V ) is used for
regulation. The load current is to be ( 4.0 m A ) and the unregulated input is
( 10.0 V . ) What should be the value of
series resistor ( boldsymbol{R}_{s} )
12
697 A lamp consumes only ( 50 % ) of maximum power applied in an AC circuit. What will be the phase difference between applied voltage and circuit current?
A ( cdot frac{pi}{3} r a d )
B. ( frac{pi}{6} r a d )
c. ( frac{pi}{4} r a d )
D. ( frac{pi}{2} r a d )
12
698 A step down transformer having efficiency of ( 75 % ) supplies 3
ampere current at 120 volt. Calculate
the current in its primary coil, if it is operated at 440 volt.
( A cdot 2 )
B.
( c cdot 3 )
D. 4
12
699 A step-down transformer converts
transmission line voltage from ( 11000 V )
to ( 220 V ) The primary of the transformer has 6000 turns and the efficiency of the transformer is ( 60 % ). If the output power
is ( 9 k W, ) then the input power will be
( mathbf{A} cdot 11 k W )
в. ( 12 k W )
c. ( 14 k W )
D. ( 15 k W )
12
700 A step-up transformer works on ( 220 mathrm{V} ) and gives 2 A to an external resistor. The
ratio of the number of turns between the
primary and secondary coils is 2: 25 Assuming ( 100 % ) efficiency, find the secondary voltage, primary current and power delivered
A . 2750 ( vee, ) 25 ( A, 5500 W )
B. 2750 V, 20 A, 5000 W
c. 2570 V, 25 A, 550
D. 2750 V, 20 A, 55 W
12
701 toppr
Q Type your question
3
( c )
( D )
12
702 A power transmission line feeds input power at ( 2300 V ) to a step-down transformer, with its primary winding having 4000 turns. What should be the
number of turns in the secondary winding in order to get output power at
( mathbf{2 3 0} boldsymbol{V} ? )
A . 300
в. 250
( c .400 )
D. 450
12
703 Leading is ( frac{x}{1000} H ) 12
704 If the frequency of an A.C is made 4 times of its initial value, the inductive
reactance will
( A cdot ) be 4 times
B. be 2 times
c. be half
D. remain the same
12
705 The instantaneous values of alternating
current and voltages in a circuit are
given as
( i=frac{1}{sqrt{2}} sin (100 pi t) ) ampere
( e=frac{1}{sqrt{2}} sin (100 pi t+pi / 3) ) volt
The average power in Watts consumed in the circuit is –
A. ( frac{sqrt{3}}{4} )
в.
( c cdot frac{1}{8} )
D.
12
706 The resistance ( R=10 Omega ), inductance ( L= )
( 2 mathrm{mH} ) and capacitance ( operatorname{cof} 5 mu F ) are
connected in same to an AC source of
frequency ( 50 mathrm{Hz} ), then at resonance the impedance of circuit is
A. zero
B. ( 10 Omega )
c. ( 1000 Omega )
D. ( 10 k Omega )
12
707 connected to a resistance ( R ) and two
ideal inductors ( L_{1} ) and ( L_{2} ) through a
switch ( S ) as shown. There is no mutual
inductance between the two inductors.
The switch ( S ) is initially open. At ( t=0 )
the switch is closed and current beings
to flow. Which of the following options is/are correct?
A. After a long time, the current through ( L_{1} ) will be ( frac{V L_{2}}{R L_{1}+L_{2}} )
B. After a long time, the current through ( L_{2} ) will be ( frac{V L_{2}}{R L_{1}+L_{2}} )
c. The ratio of the currents through ( L_{1} ) and ( L_{2} ) is fixed at all times ( (t>0) )
Det the current through the resistance ( R ) is ( frac{V}{R} )
12
708 State whether given statement is True or False

The resistor voltage is always out of phase with the current.
A. True
B. False

12
709 42. What is the amount of power delivered by the ac source
in the circuit shown (in watts).
Xc = 1222 R = 522
Xi = 8 12 R2 = 622
Ems = 130V
(a) 500 watt
(c) 1514 watt
(b) 1014 watt
(d) 2013 watt
12
710 The given graph shows variation with
time in the source voltage and steady
state current drawn by a series RLC
circuit.

Which of the following statements
is/are correct?
This question has multiple correct options
A. Current lags the voltage
B. Resistance in the circuit is ( 250 sqrt{3} Omega )
C. Reactance in the circuit is ( 250 Omega )
D. Average power dissipation in the circuit is ( 20 sqrt{3} mathrm{w} )

12
711 A resistor of resistance ( 100 Omega ) is
connected to an AC source ( varepsilon= )
( (12 V) sin left(250 pi s^{-1}right) t . ) Find the energy
dissipated as heat during ( t=0 ) to ( t= )
1.0 ms.
12
712 The reactance of a ( 2.00 mu F ) capacitor at a frequency of ( 50.0 H z ) is ( frac{x}{10} k Omega . ) Find ( x ) 12
713 If the resistance is removed from the
circuit and the value of induction is
doubled, then the variation of current with time in the new circuit is given as ( frac{x}{100} cos 314 t . ) The value of ( x ) is
12
714 A transformer of efficiency ( 90 % ) has
turns ratio ( 1: 10 . ) If the voltage across
the primary is ( 220 V ) and current in the
primary is ( 0.5 A ), then the current in
secondary is
( mathbf{A} cdot 5.5 A )
B. ( 5 A )
( c cdot 4 A )
D. ( 4.5 ~ A )
12
715 The Sl unit of inductance, henry, can be written as:
A. weber/ampere
B. volt second/ampere
c. joule/ampere ( ^{2} )
D. all of these
12
716 What do you mean by resonance in
( L C R ) series circuit? Write the formula
for resonant frequency.
12
717 If in a transformer the number of turns
of primary coil and secondary coil are 5 and 4 respectively and ( 240 mathrm{V} ) is applied to primary coil, then the ratio of current
in primary and secondary coil is
A .4: 5
B. 5: 4
( c cdot 5: 10 )
D. 8: 12
12
718 ( ln ) a ( A C ) circuit the current is given by ( boldsymbol{i}=mathbf{5} sin left(mathbf{1 0 0 t}-frac{boldsymbol{pi}}{mathbf{2}}right) ) and ( boldsymbol{V}= )
( 200 sin (100 t) V ) then power
consumption is
( mathbf{A} cdot 20 W )
в. ( 1000 mathrm{W} )
c. ( 500 W )
D. ( 0 W )
12
719 resistor R connected
15. The diagram shows a capacitor C and a resistor con
in series to an ac source. V, and V2 are voltmeters and
is an ammeter
Consider now the following statements
I. Readings in A and V, are always in phase
II. Reading in V, is ahead in phase with reading in V,
III. Readings in A and V, are always in phase which of these
statements are/is correct
(a) I only
(b) II only
(c) I and II only (d) II and III only
12
720 In the circuit of given figure (1) and (2) are ammeters. Just after key ( boldsymbol{K} ) is pressed to complete the circuit, the reading is
A. maximum in both 1 and 2
B. zero in both 1 and 2
c. zero in 1 , minimum in 2
D. maximum in 1, zero in 2
12
721 For the given circuit, the natural
frequency is given by :
( mathbf{A} cdot frac{1}{2 pi} sqrt{L C} )
B. ( frac{1}{2 pi sqrt{L C}} )
( c cdot sqrt{frac{l}{C}} overline{underline{l}} )
D. ( sqrt{frac{c}{L}} )
12
722 When ( 4 V ) DC is connected across an
inductor, current is ( 0.2 A . ) When ( A C ) of
( 4 V ) is applied the current is ( 0.1 A ) Then self inductance of the coil is:
( left[text { Given } omega=1000 text { rads}^{-1}right] )
A ( .20 mathrm{mH} )
в. ( 40 mathrm{mH} )
c. ( 20 sqrt{3} mathrm{mH} )
D. none of these
12
723 A transformer steps up an ( A C ) supply from ( 220 V ) to ( 2200 V . ) If the secondary
coil of the transformer has 2000 turns, the number of turns in its primary coil will be:
A . 200
в. 100
c. 50
D. 20
12
724 In an LCR circuit the potential
difference between the terminal of the
inductance is ( 60 V ), between the
terminals of the capacitor is ( 30 V ) and
that between the terminals of the
resistance is ( 40 mathrm{V} ). The supply voltage
will be equal to:
( mathbf{A} cdot 130 V )
в. ( 10 V )
( c .50 V )
D. ( 70 V )
12
725 Statement 1: An emf ( in=€_{0} )
( sin left(omega t+frac{pi}{6}right) ) is applied in a circuit and a current of ( i=i_{0} sin left(omega t-frac{pi}{3}right) ) flows
Then the average power delivered by the source is zero.

Statement 2: If the average value of ( in )
and ( i ) is separately zero, then the power
consumed will be zero.
A. Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement- –
B. Statement-1 is True, Statement-2 is True; Statement-2
is not a correct explanation for Statement-
c. Statement-1 is True, Statement-2 is False
D. Statement-1 is False, Statement-2 is True.

12
726 The self-inductance of the motor of an
electric fan is ( 10 mathrm{H} ). In order to impart maximum power at ( 50 mathrm{Hz} ), it should be
connected to a capacitance of : (Take ( pi^{2} ) ( =10) )
A ( .4 mu F )
в. ( 8 mu F )
c. ( 1 mu F )
D. ( 2 mu F )
12
727 An inductor ( 20 mathrm{mH} ), a capacitor ( 100 mu mathrm{F} ) and a resistor ( 50 Omega ) are connected in
series across a source of emf, ( mathrm{V}=10 )
( sin 314 t . ) The power loss in the circuit is?
A . 2.74 w
в. 0.79 w
c. ( 1.13 mathrm{w} )
D. ( 0.43 mathrm{w} )
12
728 Write any four differences between
step-up and step-down transformer
12
729 What is the approximate peak value of an alternating current producing four times the heat produced per seconds by a steady current of ( 2 mathrm{A} ) in a resistor?
A ( .2 .8 mathrm{A} )
в. 4.0 А
c. 5.6 A
D. 8.0 A
12
730 The time taken by the current to rise to 0.63 of its maximum value in a d.C
circuit containing inductance ( (boldsymbol{L}) ) and
resistance ( (boldsymbol{R}) ) depends on
A. ( L ) only
B. ( R ) only
c. ( frac{L}{R} ) only
D. ( L R ) only
12
731 An inductance of ( 2.0 mathrm{H} ),a capacitance of 18 and a resistance of 10 are connected
to an ( A C ) source of 20 with adjustable frequency
(a) What frequency should be chosen to maximum the current (RMS)
in the circuit?
(b) What is the value of
this maximum current (RMS)?
12
732 What is the phase angle of the source voltage with respect to the current? Does the source voltage lag or lead the current? 12
733 To reduce the resonant frequency in an
LCR series circuit with a generator
A. the generator frequency should be reduced.
B. another capacitor should be added in parallel to the first.
C. the iron core of the inductor should be removed.
D. dielectric in the capacitor should be removed
12
734 An ( L-C ) circuit consists of an
inductor of ( L=0.0900 H ) and a
capacitor of ( C=4 times 10^{-4} F . ) The initial
charge on the capacitor is ( 5.00 mu C ) and the initial current in the inductor is
zero. When the current in the inductor
has half its maximum value, what is
the energy stored in the inductor?
A ( .7 .8 times 10^{-9} J )
B . ( 9.8 times 10^{7} J )
c. ( 7.8 times 10^{7} J )
D. ( 9.8 times 10^{-7} J )
12
735 In L-C oscillation the maximum charge on the capacitor can be ( Q ). If at any instant, electric energy and magnetic energy associated with the current is
equal, then the charge on the capacitor at that instant is :
A ( cdot frac{Q}{sqrt{2}} )
в. ( frac{Q}{2} )
c. ( frac{3 Q}{sqrt{2}} )
D. ( frac{3 Q}{2} )
12
736 An inductance coil of ( 1 H ) and ( a )
condenser of capacity ( 1 p F ) produce
resonance. The resonant frequency will be
( ^{text {A }} cdot frac{10^{6}}{pi} H z )
в. ( 27 pi times 10^{6} mathrm{Hz} )
c. ( frac{2 pi}{10^{6}} H z )
D. ( frac{10^{6}}{2 pi} H z )
12
737 7.
3. An inductor of inductance L and resistor of resistance
R are joined in series and connected by a source of
frequency w. Power dissipated in the circuit is
2 (R²+ w²1²)
V²R
ov
(R? + oʻL?)
(b)
_
V
(C)
(d)
²
& VR² + w²1²
(R+ oʻL)
(AIEEE 2002)
anca of anu transformer is laminated to
12
738 In the electrical network, at ( t<0 ) (as
given in the figure), key is placed on (1)
till the capacitor got fully charged. Key
is placed on (2) at ( t=0 . ) Time when the
energy in both the capacitor and the
inductor will be same for the first time
is
A ( cdot frac{pi}{4} sqrt{L C} )
B. ( frac{3 pi}{4} sqrt{L C} )
C ( cdot frac{pi}{3} sqrt{L C} )
D. ( frac{2 pi}{3} sqrt{L C} )
12
739 A series LCR circuit containing a resistance of ( 120 Omega ) has angular frequency ( 4 times 10^{5} ) rad ( / mathrm{s} ). At resonance
the voltages across resistance and inductance are ( 60 mathrm{V} ) and ( 40 mathrm{V} )
respectively. The angular frequency at which the current in the circuit lags the voltage by ( frac{pi}{4} ) is:
A ( cdot 2 times 10^{5} r a d / s )
B . ( 6 times 10^{5} mathrm{rad} / mathrm{s} )
c. ( 8 times 10^{5} r a d / s )
D. ( 10 times 10^{5} mathrm{rad} / mathrm{s} )
12
740 In LCR series circuit, an alternating
e.m.f. ‘e’ and current ‘i’ are given by the equations ( e=100 sin (100 t) ) volt, ( i= )
( mathbf{1 0 0} sin left(mathbf{1 0 0}+frac{boldsymbol{pi}}{mathbf{3}}right) mathrm{m} mathrm{A} . ) The average
power dissipated in the circuit will be
( mathbf{A} cdot 100 mathrm{w} )
B. 10w
( c .5 w )
D. 2.5w
12
741 Turn ratio in a setup transformer is ( 1: 2.1 mathrm{f} ) a lechlanche cell of ( 1.5 mathrm{V} ) is connected
across the input, what is the voltage across the output?
A . ( 1.5 v )
B. 0.0
( c cdot 3 v )
D. 0.75 ( v )
12
742 Compute the energy stored in the
inductor at ( t=2.00 m s )
A. ( 0.0094 mu J )
B. ( 0.0940 mu J )
c. ( 0.9400 mu J )
D. ( 9.4000 mu J )
12
743 When induced emf in inductor coil is
( 50 % ) of its maximum value then stored
energy in inductor coil in the given
circuit will be-
A ( .2 .5 m J )
( mathbf{B} cdot 5 m J )
c. ( 15 m J )
D. 20.5
12
744 The Figure 26.67 shows variation of ( R )
( X_{L} ) and ( X_{C} ) with frequency fin a series
L, C, R circuit. Then, for
what frequency point, the circuit is inductive?
( A )
B.
( c )
‘. all point
12
745 An A.C. of ( 50 mathrm{Hz} ) and ( 1 mathrm{A} ) peak value flows
in primary coil transformer whose mutual inductance is ( 1.5 mathrm{H} ). Then peak
value of induced emf in the secondary coil is:
A. ( 150 v )
B. ( 150 pi v )
c. ( 300 vee )
D. 200 V
12
746 A ( 120 V, 60 H z ) a.c. power is connected ( 800 Omega ) non-inductive resistance and unknown capacitance in series. The voltage drop across the resistance is found to be ( 102 mathrm{V} ), then voltage drop across capacitor is
( A cdot 8 v )
B. 102v
( c cdot 63 v )
D. ( 55 v )
12
747 For an ( L C R ) series circuit with an A.C.
source of angular frequency ( omega, ) which statement is correct?
A cdot circuit will be capacitive if ( omega>frac{1}{sqrt{L C}} )
B. circuit will be capacitive if ( omega=frac{1}{sqrt{L C}} )
c. Power factor of circuit will be unity if capacitive reactance equals inductive reactance
D. current will be leading voltage if ( omega>frac{1}{sqrt{L C}} )
12
748 ( mathbf{A} )
12 ohm resistor and a 0.21 henry
inductor are connected in series to an
AC source operating at ( 20 v ) olts, 50 cycle/second. The phase angle between the current and the source voltage is
A ( .30^{circ} )
В . ( 40^{circ} )
( c cdot 80^{circ} )
D. ( 90^{circ} )
12
749 A voltage of peak value ( 283 mathrm{V} ) and varying frequency is applied to series LCR combination in which ( R=3 Omega, L=25 )
( mathrm{mH} ) and ( mathrm{C}=400 mu mathrm{F} ). Then the frequency (in ( mathrm{Hz} ) ) of the source at which maximum power is dissipated in the above is
A . 51.5
B. 50.7
( c . ) 51.
D. 50.3
12
750 If resistance of ( 100 Omega ) and the
inductance of 0.5 henry and capacitance of ( 10 times 10^{6} ) farad are
connected in series through ( 50 mathrm{Hz} ) A.C supp;y, then impedence is
A. ( 1.8765 Omega )
B. ( 18.76 Omega )
c. ( 187.6 Omega )
D. 101.3Omega
12
751 The cross-over frequency ( f_{c} ) is
A ( cdot frac{1}{2 pi sqrt{L C}} )
B. ( frac{1}{2 pi R C} )
c. ( frac{R}{2 pi I} )
D. none
12
752 A power transformer (step-up) with an 1: 8 turn ratio has ( 60 H z, 120 V ) across
the primary; the load in the secondary is
( 10^{4} Omega . ) The current in the secondary is
( mathbf{A} cdot 96 A )
B . ( 0.96 A )
( c .9 .6 A )
D. ( 96 m A )
12
753 Complete the diagram of the transformer and connections by labelling all parts joined by you. 12
754 A ( 120 V A C ) line transformer is to supply ( 13000 V ) for a neon sign. To reduce shock hazard a ( 8.5 mathrm{mA} ) fuse is inserted. Find the
maximum input power that can be given to the transformer.
( mathbf{A} cdot 120 W )
B. ( 121 W )
( c cdot 110 W )
D. ( 104 W )
12
755 A choke coil has negligible resistance.
The alternating potential drop across it is 220 volts and the current is ( 5 mathrm{mA} ). The
power consumed is
A ( cdot 220 times frac{5}{1000} W )
в. ( frac{220}{5} W )
c. zero
D. ( 2.20 times 5 W )
12
756 57. The total heat produced in resistor Rin an RL circuit when
the current in the inductor decreases from 1 to 0 is
(a) LI?
(b) ELIE
12
757 The primary of a transformer has 400
turns while the secondary has 2000 turns. If the power output from the secondary at ( 1000 V ) is ( 12 k W, ) what is
the primary voltage?
( mathbf{A} cdot 200 V )
B. ( 300 V )
c. ( 400 V )
D. ( 500 V )
12
758 A light bulb is rated at ( 100 W ) for a
( 220 V ) supply. Find the rms current through the bulb:
( mathbf{A} cdot 0.25 A )
в. ( 0.45 A )
c. ( 0.65 A )
D. ( 0.85 A )
12
759 Two inductors of inductance L each are
connected in series with opposite
magnetic fluxes. The resultant inductance is (Ignore mutual inductance)
A. zero
B.
c. 2L
D. 3L
12
760 has an inductor of inductance ( L ) and a
resistor of resistance it connected in
series. Using the phasar diagram,
explain why the voltage in the circuit
will lead the current in phase.
(b) The potential difference across the
resistor is ( 160 % ) and that across the
inductor is ( 120 V . ) Find the effective
value of the applied voltage. If the
effective current in the circuit be ( 1.0 A )
calculate the total impedance of the circuit.
(c) What will be the potential difference
in the circuit when direct current is
passed through the circuit??
12
761 In an R-C circuit, select the correct
options among the following:
This question has multiple correct options
A. Instantaneous A.C is given by ( I=I_{0} sin (w t+phi) )
B. The alternating current in the circuit leads the emf by a phase angle
C. Its impedance is ( sqrt{R^{2}+(w C)^{2}} )
D. Its capacitive reactance is ( omega C )
12
762 For the circuit shown in the figure,
which of the following statements is
true?
A. With S1 closed ( V 1=15 V, V 2=20 V )
B. With ( S_{3} ) closed, ( V_{1}=V_{2}=25 mathrm{V} )
C. With ( S_{1} ) and ( S_{2} ) closed, ( V_{1}=V_{2}=0 )
D. With ( S_{1} ) and ( S_{3} ) closed, ( V_{1}=30 vee, V_{2}=20 mathrm{V} )
12
763 ( A 60 mu F ) capacitor is connected to a 110 ( mathrm{V}(mathrm{rms}), 60 mathrm{Hz} ) ac supply. The rms value of Current in the circuit is:
A . 1.49 A
B. 14.9 A
c. 2.49 A
D. 24.9 A
12
764 ITOS
ILLUSTRATION 24.2 A voltage, E = 60 sin(314t), is applied
across a resistor of 20 92. What will be the reading of Ime
(a) in an ac ammeter?
(b) in an ordinary moving coil ammeter in series with the
resistor?
пете!
12
765 The Figure shows a parallel ( L-C-R )
circuit connected to a variable
frequency 200V source. L ( =5 mathrm{H}, mathrm{C}=80 mu mathrm{F} )
and ( R=40 Omega ). What is the ems
current in the circuit at resonance?
( A cdot 5 A )
B. 10 A
c. ( frac{5}{sqrt{2}} )
D. ( 5 sqrt{2} A )
12
766 In the AC circuit shown, ( X_{L}=7 Omega, R= )
( 4 Omega ) and ( X_{c}=4 Omega . ) The reading of the
ideal voltmeter ( V_{2} ) is ( 8 sqrt{2} ). The reading
of idea voltmeter ( V_{1} ) will be :
A. 20 volt
B. 7 volt
( c cdot 8 ) volt
D. 10 volt
12
767 An alternative voltage given by ( V= ) ( 140(sin 314 t) ) is connected across a
pure resistor of ( 50 Omega ). Find
(i) The frequency of the source.
(ii) The rms current through the
resistor.
12
768 A circuit element shown in the figure as
box is having either a capacitor or an
inductor. The power factor of the circuit
is ( 0.8, ) which current lags behind the
voltage. The source voltage ( V )
12
769 Find the maximum value of ( boldsymbol{I} ) 12
770 7. In an LCR series AC circuit, the voltage across each
the components, L, C, and R, is 50 V. The voltage across
the LC combination will be
(a) 50 V
(6) 5012 V
(c) 100 V
(d) 0 V (zero) (AIEEE 2004
12
771 In an ideal parallel LC circuit, the capacitor is charged by connecting it to a D.C. source which is then
disconnected. The current in the circuit
A. Becomes zero instantaneously
B. Grows monotonically
c. Decays monotonically
D. oscillates instantaneously
12
772 A transformer has 50 turns in the
primary and 1000 turns in the secondary. If the primary is connected
to a ( 220 V ) DC supply, what will be the voltage across the secondary?
12
773 A series LCR circuit is tuned to resonance
If the angular frequency of the applied AC voltage at resonance is ( omega ), the impedance
of the circuit then is:
A ( cdot R+omega L+left(frac{1}{omega C}right) )
B.
c. ( sqrt{R^{2}+omega L+left(frac{1}{omega C}right)^{2}} )
D. ( sqrt{R^{2}+left(omega L-frac{1}{omega C}right)^{2}} )
12
774 In which of the following devices, the eddy current effect is not used?
A. Induction furnace
B. Magnetic breaking in train
c. Electromagnet
D. Electric heater
12
775 When ( I ) is equal to one half of its maximum value, what is the value of
( |Q| ? )
12
776 At grid sub-stations the voltage is stepped up to reduce loss of
A. current
B. electrical energy
c. power
D. resistance
12
777 A step-down transformer is used to light
( 12 V ) lamp from a ( 240 V ) mains
supply. The lamp lights at normal brightness. The primary coil
has 600 turns.

How many turns are in the secondary
coil?
A .12
B. 20
( c .30 )
D. 50

12
778 What is the range between ( f_{1} ) and ( f_{2} ) of
an RLC circuit that resonates at
( 150 k H z ) and has a ( Q ) of ( 30 ? )
A . ( 100.0 k H z ) to ( 155.0 k H z )
B. ( 147.5 k H z ) to ( 152.5 k H z )
c. ( 4500 k H z ) to ( 295.5 k H z )
D. ( 149970 H z ) to ( 150030 H z )
12
779 A choke coil is needed to operate an arc ( operatorname{lamp} operatorname{at} 160 V(mathrm{rms}) ) and ( 50 mathrm{Hz} ). The arc
lamp has an effective resistance of ( 5 Omega ) when running at ( 10 A(mathrm{rms}) . ) Calculate
the inductance of the choke coil. If the
same arc lamp is to be operated on ( 160 V ) DC, what additional resistance
would be required. Compare the power losses in both the cases.
12
780 The magnetic field energy in an inductor changes from maximum value to minimum value in ( 5.0 m s, ) when
connected to an ( A C ) source. The
frequency of the source is
( A cdot 20 H z )
B. 50 Н
c. 200 н ( z )
D. 500 нz
12
781 What is resonance circuit? An
alternating current circuit consenting L-C-R is connected to a A.C.
voltage source in series. Determine:
A. Resultant voltage
B. Impedance
c. Resonance frequency
D. None of these above
12
782 If a fully charged capacitor ( C ) with
initial charge ( q_{0} ) is connected to a coil of
self inductance ( L ) at ( t=0 . ) The time at
which the energy is stored equally between the electric field and magnetic
field is :
A ( . pi sqrt{L C} )
в. ( frac{pi}{4} sqrt{L C} )
c. ( frac{pi}{2} sqrt{L C} )
D. ( frac{pi}{6} sqrt{L C} )
12
783 Current flowing through the circuit 12
784 Transformer ( rightarrow ) ideal ( rightarrow boldsymbol{E}_{boldsymbol{P}}= )
( mathbf{1 0 0 0} boldsymbol{V}, boldsymbol{I}_{boldsymbol{P}}=mathbf{5 0 A} )
( 220 V rightarrow 80 ) houses
Resistance of secondary coil will be
A . ( 2 Omega )
B. 3Omega
( c .1 Omega )
D. ( 4 Omega )
12
785 31. An LCR circuit contains resistance of 100 22 and a supply
of 200 V at 300 rad angular frequency. If only capacitance
is taken out from the circuit and the rest of the circuit is
joined, current lags behind the voltage by 60°. If, on the
other hand, only inductor is taken out, the current leads
by 60° with the applied voltage. The current flowing in
the circuit is
(a) 1A
(b) 1.5 A
(c) 2 A
(d) 2.5 A
12
786 A transformer having efficiency of ( 75 % ) is working on ( 220 V ) and ( 4.4 k W ) power supply. If the current in the secondary coil is ( 5 A . ) What will be the voltage
across secondary coil and the current in primary coil?
( mathbf{A} cdot V_{s}=220 V, i_{p}=20 A )
B. ( V_{s}=660 V, i_{p}=15 A )
C . ( V_{s}=660 V, i_{p}=20 A )
D. ( V_{s}=220 V, i_{p}=15 A )
12
787 0001
155
25. An inductor (L = 0.03 H) 0.03 H
0.15 k92
and a resistor (R = 0.15 k92)
are connected in series to a
battery of 15 V EMF in a circuit
shown below. The key Khas L E
been kept closed for a long time.
Then at t = 0, K, is opened and
key K, is closed simultaneously. At t = 1 ms, the current
in the circuit will be (@=150)
(a) 100 mA
(b) 67 mA
(c) 6.7 mA
(d) 0.67 mA
(JEE Main 2015)
12
788 The reactance of coil when used in an
A.C. power supply ( 220volts, 50 cycles/sec) is 50ohms. The inductance of the coil is nearly
A . 0.16 Н
B. 0.22
c. ( 2.2 mathrm{H} )
D. 1.6
12
789 An inductor ( 10 Omega / 60^{circ} ) is connected to a
( 5 Omega ) resistance in series. Find net
impedance.
A . ( 15 Omega )
B. ( 12 Omega )
c. ( 13.2 Omega )
D. ( 18 Omega )
12
790 The transformer turns ratio is 1: 5 and
( 0.4 mathrm{A} ) current flows through the second
when power developed across it is 200
W. Calculate secondary voltage
A . 2000 v
B. 1500 v
c. ( 1000 mathrm{v} )
D. 500 v
12
791 A transformer steps up an AC supply
from ( 220 mathrm{V} ) to ( 2200 mathrm{V} ). If the secondary coil of the transformer has 2000
turns,the number of turns in its primary coil will be:
A . 200
B. 100
( c .50 )
D. 20
12
792 Find the value of an inductance which
should be connected in series with a
capacitor of ( 5 mu F, ) a resistance of ( 10 Omega )
and an ac source of ( 50 H z ) so that the
power factor of the circuit is unity.
A ( cdot frac{20}{pi^{4}} )
в. ( frac{20}{pi^{2}} )
c. ( frac{20}{pi^{3}} )
D. ( frac{20}{pi^{5}} )
12
793 A series R-C circuit is connected to an
alternating voltage source. Consider two situation:
(a) When capacitor is filled
(b) When capacitor is mica filled Current through resister is i and voltage across capacitor is ( V ) then :
A ( . V_{a}=V_{b} )
в. ( V_{a}V_{b} )
( mathbf{D} cdot i_{a}=i_{b} )
12
794 Assertion
In a series ( L C R ) circuit, at resonance
condition power consumed by circuit is
maximum.
Reason
At resonance condition, the effective
resistance of circuit is maximum.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect
12
795 A ( 10 Omega ) resistance, ( 5 mathrm{mH} ) coil and ( 10 mu mathrm{F} )
capacitor are joined in series. When a suitable frequency alternating current source is joined to the combination, the circuit resonates. If the resistance is
halved the resonance frequency is
A. halved
B. doubled
c. remains same
D. quadrupled
12
796 The transformation ratio of a step up
transformer is :
A. greater than one
B. less than one
C. less than one and some times greater than one
D. greater than one and some times less than one
12
797 ( ln ) an ( mathrm{AC} ) circuit, ( V ) and ( I ) are given below,
then the power dissipated in the circuit:
( V=50 sin (50 t) V, I=50 sin left(50 t+frac{pi}{3}right) m A )
A. ( 0.625 W )
В. ( 1.25 mathrm{W} )
c. ( 2.50 W )
D. ( 5.0 W )
12
798 For the circuit shown in the Figure, the current through the inductor is ( 0.9 A )
while the current through the condenser
is ( 0.4 A )
A. current drawn from generator ( 1=1.13 mathrm{A} )
B. ( omega=frac{1}{(1.5 L C)} )
( mathbf{C} cdot I=0.5 mathrm{A} )
( D cdot I=0.6 A )
12
799 If a capacitor is connected to two
different A.C. generators, then the value of capacitive reactance is:
A. directly proportional to frequency
B. inversely proportional to frequency
C. independent of frequency
D. inversely proportional to the square of frequency
12
800 ( ln operatorname{an} A C ) circuit ( V ) and ( I ) is given by
( boldsymbol{V}=mathbf{1 0 0 0} sin (mathbf{1 0 0 0} boldsymbol{t}) ) volt
( boldsymbol{I}=mathbf{1 0 0} sin left(mathbf{1 0 0 0} boldsymbol{t}+frac{boldsymbol{pi}}{mathbf{6}}right) boldsymbol{m} boldsymbol{A} )
The power dissipation in the circuit in one complete cycle is.
( mathbf{A} cdot 25 W )
B. ( 25 sqrt{3} )
c. ( 100 mathrm{W} )
D. 10 W
12
801 In a LCR series resonating circle circuit Give the value of average power loss. 12
802 A ( 0.2 Omega ) resistor and ( 15 mu ) rapacitor are connected in series to a ( 220 mathrm{V}, 50 mathrm{Hz} ) ac source. The impedance of the circuit is
A . ( 250 Omega )
в. ( 268 Omega )
c. ( 29.15 Omega )
D. ( 291.5 Omega )
12
803 22. In the circuit given in the figure, Vc = 50 V and R= 50 S2.
The values of C and VR are
[vc=50v
110 V
60 Hz
R= 50 2 3
(a) 3.3 mF, 60 V
(c) 52 uF, 98 V
(b) 104 uF, 98 V
(d) 2 uF, 60 V
12
804 A step-up transformer of turns ratio 2: 1 has ( 50 mathrm{Hz} ) AC voltage applied to primary The frequency of AC output voltage across secondary is :
A. zero
B. 25 Hz
c. 50 нz
D. 100 нz
12
805 Calculate the resonant frequency and ( Q )
factor (Quality factor) of a series L-C-R circuit containing a pure inductor of inductance ( 4 mathrm{H} ), capacitor of
capacitance ( 27 mu F ) and resistor of resistance ( 8 cdot 4 Omega )
12
806 The inductive reactance of a coil is
( 2500 Omega . ) On increasing its selfinductance three times, the
new inductive reactance will be
A. ( 7500 Omega )
B. 2500 Omega
c. ( 1225 Omega )
D. zero
12
807 In a series resonant ( L C R ) circuit, the
voltage across ( boldsymbol{R} ) is 100 volts and ( boldsymbol{R}= )
( 1 k Omega ) with ( C=2 mu F . ) The resonant
frequency is 200 rad/s. At resonance
the voltage across ( L ) is
A. ( 4 times 10^{-3} V )
В. ( 2.5 times 10^{-2} V )
c. ( 40 V )
D. 250 V
12
808 In a parallel L-C-R circuit spring constant ( K ) is analogous to:
A .
B.
( c cdot 1 / L )
D. ( 1 / c )
12
809 The capacitive reactance at ( 1600 H z ) is
81 Omega. When the frequency is doubled then capacitive reactance will be
A . ( 40.5 Omega )
в. ( 81 Omega )
( c cdot 162 Omega )
D. Zero
12
810 When resonance is produced in a series
( L C R ) circuit, then which of the following
is not correct?
A. Current in the circuit is in phase with the applied voltage
B. Inductive and capacitive reactance are equal
C. If ( R ) is reduced, the voltage across capacitor wil increase
D. Impedance of the circuit is maximum.
12
811 If ( 25 W ) of power are applied to the primary of an ideal transformer with a
turns ratio of ( 10, ) the power delivered to the secondary load is
A ( .25 W )
B. ( 0 W )
c. ( 250 W )
D. ( 2.5 W )
12
812 State whether given statement is True or False

Apparent power is expressed in watts.
A. True
B. False

12
813 6. Alternating current cannot be measured by a DC ammeter
because
(a) AC cannot pass through DC ammeter
(b) AC changes direction
(c) the average value of current for complete cycle is zero
(d) DC ammeter will get damaged (AIEEE 2004)
A

it the oltogo
12
814 The efficiency of a transformer is ( 98 % ) The primary voltage and current are ( 200 V ) and ( 6 A . ) If the secondary voltage is ( 100 V ), the secondary current is :
A . ( 11.76 A )
B. ( 12.25 A )
c. ( 3.06 A )
D. ( 2.94 A )
12
815 An ideal inductor takes a current of ( 10 A )
when connected to a ( 125 V, 50 H z A C )
supply. A pure resistor across the same
source takes 12.5 A. If the two are
connected in series across a ( 100 sqrt{2} V )
( 40 H z ) supply, the current through the circuit will be
( mathbf{A} cdot 10 A )
B. ( 12.5 A )
( c .20 A )
D. ( 25 A )
12
816 An A.C. of ( 50 mathrm{Hz} ) and ( 1 mathrm{A} ) peak value flows
in primary coil transformer whose mutual inductance is ( 1.5 mathrm{H} ). Then peak
value of induced emf in the secondary coil is:
A. ( 150 v )
B. ( 150 pi v )
c. ( 300 vee )
D. 200 V
12
817 Two resistors are connected in series
( operatorname{across} ) a ( 5 ~ V ) rms source of alternating potential. The potential difference ( operatorname{across} 6 Omega ) resistor is ( 3 V . ) If ( R ) is
replaced by a pure inductor ( L ) of such
magnitude that current remains same, then the same potential difference ( operatorname{across} L ) is:
( mathbf{A} cdot 1 V )
B. ( 2 V )
c. ( 3 V )
D. ( 4 V )
12
818 A series LCR-circuit with ( boldsymbol{R}=mathbf{2 0} boldsymbol{Omega} )
( boldsymbol{L}=mathbf{1 . 5} boldsymbol{H} ) and ( boldsymbol{C}=mathbf{3 5} boldsymbol{mu} mathrm{F} ) is connected
to a variable frequency ( 200 V ) ac supply When the frequency of the supply equals the natural frequency of the circuit, the average power transferred to the circuit in one complete cycle is?
( mathbf{A} cdot 200 W )
в. ( 2000 mathrm{W} )
( c .100 W )
D. ( 4000 mathrm{W} )
12
819 A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load.
The ratio of the turns in primary and secondary coil is ( 20: 1 . ) If transformer efficiency is ( 100 % ), then the current flowing in primary coil will be :
( A cdot 8 A )
в. ( 4 A )
( c .5 A )
D. ( 9 A )
12
820 State whether given statement is True or False

A reflective load is a load as it appears
to the source in the primary of a transformer.
A. True
B. False

12
821 5. Voltage and current in an ac circuit are given by
V = 5 sin ( 1001t – and 1 = 4 sin 1007t +-
(a) Voltage leads the current by 30°
(b) Current leads the voltage by 30°
(c) Current leads the voltage by 60°
(d) Voltage leads the current by 60°
12
822 ( 50 H z ) alternative current current of
crest value ( 1 A ) flows through the primary of a transformer. If mutual
inductance between the primary and secondary is ( 0.5 ~ H, ) then crest voltage
induced in the secondary is:
( mathbf{A} cdot 100 V )
B. ( 150 V )
( mathrm{c} .75 mathrm{V} )
D. ( 50 V )
12
823 An inductance of negligible resistance whose reactance is ( 22 Omega ) at ( 200 H z ) is
connected to 200 volt. If the line
frequency is known to be 50 cycles/second, the equation for the line voltage is :
A. 0.0175 Henry
B. 0.175 Henry
c. 1.75 Henry
D. 17.5 Henry
12
824 n an L-C-R circuit as shown both
switches are open initially. Now switch ( S_{1} ) and ( S_{2}, ) are closed. ( (q ) is the charge on the capacitor and ( r=R C ) is
capacitance time constant). What is the charge on the capacitor at ( t=2 tau ? )
12
825 In a series ( L, R, C ) circuit which is
connected to ac source, when resonance
is obtained then net impedance Z will
be:
A ( . Z=R )
B. ( quad Z=omega L-frac{1}{omega C} )
( mathbf{c} cdot Z=omega L )
D. ( z=frac{1}{w C} )
12
826 State whether given statement is True or False
The circuit phase angle is the angle between the total current and the
applied (source) voltage.
A. True
B. False
12
827 11. In a series resonant LCR circuit, the voltage across
R is 100 V and R = 1 k12 with C = 2 uF. The resonant
frequency ois 200 rad/s. At resonance the voltage across
L is
(a) 250 V
(b) 4 x 10-3 v
(c) 2.5 x 10-2 V (d) 40 V (AIEEE 2006)
A gonerator coil with turns oul of the come
12
828 The reading shown in AC Voltmeter
when ( mathrm{S} ) is moved to ( mathrm{B} ) is:
A . ( 120 v )
B. 100 ( v )
( c cdot 140 v )
D. ( 160 mathrm{V} )
12
829 ( ln ) an oscillating ( L-C ) circuit in which
( C=4.00 mu F, ) the maximum potential
across the capacitor during the
oscillations is ( 1.50 V ) and the maximum
current through the inductor is ( 50.0 m A )
What is the inductance ( L ? )
( mathbf{A} cdot 8.6 m H )
в. ( 3.6 m H )
c. ( 6.6 m H )
D. ( 4.6 m H )
12
830 To produce an ( 800 H z ) sine wave, a four
pole generator must be operated at
A. 200 rps
в. 400 rps
c. 800 rps
D. 1,600 rps
12
831 State whether True or False:
A series resonant circuit is commonly called a tank circuit.
A. True
B. False
12
832 Identify the graph which correctly
represents the variation of capacitive
reactance ( X_{C} ) with frequency.
( A )
B.
( c )
D.
12
833 A DC circuit contains ( 10 Omega ) of resistance
in series with ( 10 H ) coil. The impedance
of the circuit is
A . ( 10 Omega )
B. 20Omega
c. ( 1 Omega )
D. zero
12
834 Which of the following in electricity is
analogous to momentum ( m v ) in dynamics?
A. IV
B . IL
c. ( mathrm{Q} )
D. IQ
12
835 The voltage in the primary and the
secondary coils of a step up transformer are ( 200 mathrm{V} ) and ( 4 mathrm{KV} ) respectively. If the
current in the primary is 1 ampere then the current in the secondary coil will be
( A cdot 50 mathrm{m} ) A
B. 500 ( mathrm{m} ) A
( c cdot 5 A )
( D cdot 5 m A )
12
836 An inductor coil stores ( U ) energy when ( i )
current is passed through it and
dissipates energy at the rate of ( P . ) The time constant of the circuit, when this
coil is connected across a battery of
zero internal resistance is :
A ( cdot frac{4 U}{P} )
в. ( frac{U}{P} )
c. ( frac{2 U}{P} )
D. ( frac{2 P}{U} )
12
837 A capacitor ‘C’, a variable resistor’R’ and
a bulb ‘B’ are connected in series to the
ac mains in circuit as shown. The bulb
glows with some brightness. How will the glow of the bulb change if (i) a dielectric slab is introduced between
the plates of the capacitor, keeping resistance ( R ) to be the same; (ii) the
resistance ( R ) is increased keeping the
same capacitance?
12
838 A transmitter transmits at a
wavelength of ( 300 m . ) A condenser of
capacitance ( 2.4 mu F ) is being used. The
value of the inductance for the resonant
circuit is approximately
( mathbf{A} cdot 10^{-4} H )
в. ( 10^{-6} H )
c. ( 10^{-8} H )
D. ( 10^{-10} mathrm{H} )
12
839 If in a transformer the number of turns
of primary coil and secondary coil are 5 and 4 respectively and ( 240 mathrm{V} ) is applied to primary coil, then the ratio of current in primary and secondary coil is :
A .4: 5
B. 5: 4
c. 5: 10
D. 8: 12
12
840 In series L-C-R resonant circuit, to
increase the resonant frequency:
A. ( L ) will have to be increased
B. C will have to be increased
c. LC will have to be decreased
D. LC will have to be increased
12
841 With increase in frequency of an A.C.
supply, the inductive reactance
A. decreases
B. increases directly with frequency
C. increases as square of frequency
D. decreases inversely with frequency
12
842 61. A telephone wire of length 200 km has a capacitance of
0.014 uF per km. If it carries an ac of frequency 5 kHz,
what should be the value of an inductor required to be
connected in series so that the impedance of the circuit is
minimum
(a) 0.35 mH
(b) 35 mH
(c) 3.5 mH
(d) Zero
12
843 ( ln ) a circuit ( L, C, R ) are connected in
series with an alternating voltage source of frequency ( f ). The current lags
the voltage by ( 45^{0} . ) The value of ( C ) is:
A ( cdot frac{1}{pi f(2 pi f L+R)} )
B・ ( frac{1}{2 pi f(2 pi f L-R)} )
c. ( frac{1}{2 pi f(2 pi f L+R)} )
D. ( frac{1}{pi f(2 pi f L-R)} )
12
844 ( ln operatorname{an} A C ) circuit ( V ) and ( I ) are given ( V= )
( 100 sin (100 t) V ) and ( I= )
( mathbf{1 0 0} sin (mathbf{1 0 0} t+boldsymbol{pi} / mathbf{3}) boldsymbol{m m} . ) The power
dissipated in the circuit is:
A ( cdot 10^{4} ) watt
B. 10 watt
c. 2.5 watt
D. 5 watt
12
845 Draw a curve for showing variation in alternating current with frequency in LCR resonant circuit. Hence obtain an
expression of bandwidth.
12
846 For the circuit shown in the figure the
current through the inductor is ( 1.6 A )
while the current through the condenser is ( 0.4 A ), then the current ( l ) drawn from
the source is :
A ( cdot 2 sqrt{2} A )
B. ( 1.65 A )
( c .1 .2 A )
D. 2.0
12
847 In the circuit shown in figure,
This question has multiple correct options
A ( cdot V_{R}=80 V )
В. ( X_{C}=50 Omega )
c. ( V_{L}=40 V )
D. ( V_{0}=100 V )
12
848 ov
80. A circuit containing capacitors
C and CZ as shown in the
figure are in steady state with
key K, closed. At the instant
1 = 0, if K, is opened and K
is closed then the maximum
current in the circuit will be
1.= 2 uF C2 = 2 uF
Kzoo
(a) 1A
0000000
L = 0.2 mH
(b) A
(d) None
(c) 24
12
849 In a series LCR circuit ( mathbf{R}=200 ) Omega
and the voltage and the frequency of the main supply is ( 220 mathrm{V} ) and ( 50 mathrm{Hz} )
respectively. On taking out the capacitance from the circuit the
current lags behind the voltage by ( 30^{0} ) On taking out the inductor from the
circuit the current leads the voltage by
( 30^{0} . ) The power dissipated in the LCR
circuit is
A . ( 305 mathrm{W} )
B. ( 210 mathrm{W} )
c. ZeroW
D. ( 242 mathrm{W} )
12
850 The current in the shown circuit is found to be ( 4 sin left(314 t-frac{pi}{4}right) A ). Find the value of inductance 12
851 The instantaneous potential difference
between points ( A ) and ( B ) is :
A ( cdot 8 sin left(50 pi t+37 frac{pi}{180}right) )
B ( cdot 8 sin left(50 pi t-37 frac{pi}{180}right) )
c. ( 10 sin (50 pi t) )
D. ( 10 cos (50 pi t) )
12
852 Power loss (in W) in case of dc is 12
853 A capacitor of capacitance ( 2 mu F ) is connected in the tank circuit of an
oscillator oscillating with a frequency of 1 kHz. If the current flowing in the circuit is ( 2 mathrm{mA} ), the voltage across the capacitor will be :
A . ( 0.16 mathrm{v} )
B. 0.32
c. 79.5 ( v )
D. ( 159 mathrm{V} )
12
854 A choke coil and capacitor are connected in series and the current through the combination is maximum for ( A C ) of frequency ( n ). If they are connected in parallel, at what frequency is the current through the combination minimum?
( A )
в. ( n / 2 )
( c cdot 2 n )
D. None of these
12
855 15 s,
elf-
10. The self-inductance of the motor of an electric fan is
10 H. In order to impart maximum power at 50 Hz, it
should be connected to a capacitance of
(a) 2 ur
(b) 1 uF
(c) 8 uF
(d) 4uF (AIEEE 2005)
13)
in
12
856 The r.m.s current in an ac circuit is ( 1 A )
If the watt less current be ( sqrt{3} A ), Then
what is the power factor
12
857 ( ln ) a circuit ( L C=10^{-3} H, C=10^{-3} F )
Find angular frequency.
A. 1000 rad ( / ) sec
B. 100 rad/sec
c. 10 rad ( / ) sec
D. ( 10^{-3} )rad( / )sec
12
858 If we change the value of ( R ), then
A. Voltage does not change on ( L )
B. Voltage does not change on LC combination
C. Voltage does not change on ( mathrm{C} )
D. Voltage change on LC combination
12
859 When an AC voltage of ( 220 mathrm{V} ) is applied to the capacitor ( C ), then
A. the maximum voltage between plates is 220 v.
B. the current is in phase with the applied voltage
c. the charge on the plate is not in phase with the applied voltage
D. power delivered to the capacitor per cycle is zero
12
860 In the circuit shown in the figure, the
A.C. source gives a voltage ( V=20 cos )
( (2000 mathrm{t}) ) volt. Neglecting source resistance, select correct alternative(s).
This question has multiple correct options
A. The reading of voltmeter is 0 V
B. The reading of voltmeter is 5.6
C. The reading of ammeter is 1.4 A
D. The reading of ammeter is 0.47 A
12
861 A certain series resonant circuit has a
bandwidth of ( 2 k H z . ) If the existing coil
is replaced with one having a higher value of ( Q, ) the bandwidth will
A. Increase
B. Remain the same
c. Decrease
D. Be less selective
12
862 In an oscillating ( L-C ) circuit in which
( C=4.00 mu F, ) the maximum potential
across the capacitor during the oscillations is ( 1.50 V ) and the maximum
current through the inductor is ( 50.0 m A )
How much time does the charge on the capacitor take to rise from zero to its maximum value?
A. ( 0.238 mathrm{ms} )
B. ( 0.788 mathrm{ms} )
c. ( 0.488 mathrm{ms} )
D. ( 0.188 mathrm{ms} )
12
863 The reactance at a circuit Is zero. it Is
possible mat me circuit contains
This question has multiple correct options
( A . ) an inductor and a capacitor
B. an inductor but no capacitor
C. so a capacitor but no inductor
D. neitherr an inductor nor a capacitor
12
864 The capacitive reactance of a condenser
of capacity ( 25 mu mathrm{F} ) for an ( mathrm{AC} ) of frequency
( 4000 mathrm{Hz} ) will be
A ( cdot frac{5}{pi} Omega )
в. ( frac{10}{pi} Omega )
c. ( 5 pi Omega )
D. ( frac{pi}{5} Omega )
12
865 A step down transformer reduces ( 220 mathrm{V} )
to ( 11 mathrm{V} ).The primary coil draws ( 5 mathrm{A} ) current and secondary coil supplies 90A.Efficiency of the transformer will be
A . 4.4%
B. 20%
c. 33%
D. 90%
12
866 In a series LCR circuit at resonance, the
appiled ac voltage is ( 220 mathrm{V} ). If bthe potential drop across the inductance is ( 110 V, ) then the potential drop across the resistance is
A ( cdot 110 sqrt{2} V )
B. ( 110 V )
c. ( 220 V )
D. ( 220 sqrt{2} V )
12
867 A transformer consists of a coil of 1200
turns and another coil, with a total of
120 turns, which can be tapped at various places. Primary voltage is ( 240 mathrm{V} ) At which pair of terminals would you connect to a ( 12 mathrm{V}, 24 mathrm{V} ) lamp for it to be
lit normally?
12
868 A ( 2 F ) capacitor is initially charged to ( 20 V ) and then shorted across a ( 5 m H )
inductor. The angular frequency of oscillation is.
A. ( 1000 mathrm{rad} / mathrm{s} )
B. 100 rad/s
c. ( 10000 mathrm{rad} / mathrm{s} )
D. ( 10 mathrm{rad} / mathrm{s} )
12
869 In modern days incoming frequency of
radio receiver is superposed with a locally produced frequency produce intermediate frequency which is always constant. This makes tuning of the receiver very simple. This is used in
superheterodyne oscillators.
12
870 In a transformer the output current and
voltage are ( 4 mathrm{A} ) and ( 20 mathrm{V} ) respectively. If the ratio of number of turns in the
primary and secondary coil is 2: 1 respectively, what is the input current and voltage ?
( A cdot 2 A ) and 40
B. 1 A and 20
c. 4 A and ( 10 v )
D. 8 A and 40 v
12
871 ( 0.21-H ) inductor and ( a 88-Omega ) ( mathbf{A} )
resistor are connected in series to a
( 220-V, 50-H z A C ) source. The
current in the circuit and the phase angle between the current and the
source voltage are respectively. Use
( boldsymbol{pi}=mathbf{2 2} / mathbf{7} )
A ( cdot 2 A, tan ^{-1} 3 / 4 )
B. ( 14.4 A, tan ^{-1} 7 / 8 )
c. ( 14.4 A, tan ^{-1} 8 / 7 )
D. ( 3.28 A, tan ^{-1} 2 / 11 )
12
872 13. In an AC circuit, the voltage applied is E = E, sin ot. The
resulting current in the circuit is I = 1, sin (ot – T/2). The
power consumption in the circuit is given by
e Eolo
(a) P=0
(b) P= 2
(c) P= V2 Eolo
(d) P=
O
(AIEEE 2007)
Tonna noon
12
873 In a transformer the number of turns of
primary coil and secondary coil are 2.5 and 2 respectively and ( 140 mathrm{V} ) is applied on primary coil, then find the ratio of current in primary and secondary coils:
A ( cdot I_{p}: I_{s}=4: 5 )
B . ( I_{p}: I_{s}=5: 4 )
( mathrm{c} cdot I_{p}: I_{s}=4: 3 )
D. ( I_{p}: I_{s}=3: 5 )
12
874 The resonant frequency of the given RLC
circuit.
12
875 52. Figure shows an iron-cored
transformer assumed to be
Primary
coil
100% efficient. The ratio of
Secondary 6.0.2
coil
the secondary turns to the
primary turns is 1:20.
A 240 V ac supply is connected to the primary coil and a
6 12 resistor is connected to the secondary coil. What is
the current in the primary coil?
(a) 0.10 A
(b) 0.14 A
(c) 2 A
(d) 40 A
12
876 In a circuit, the frequency is ( boldsymbol{f}=frac{mathbf{1 0 0 0}}{mathbf{2} pi} )
( mathrm{Hz} ) and the inductance is 2 henry, then
the reactance will be
( A cdot 200 Omega )
в. 200 ( mu ) Omega
c. ( 2000 Omega )
D. 2000 ( mu Omega )
12
877 The core of a transformer is laminated
to reduce
A. flux leakage
B. hysteresis
c. copper loss
D. eddy current
12
878 In an LC circuit the capacitor has
maximum charge qo. The value of ( left(frac{d I}{d t}right)_{max } )
A ( cdot frac{q_{0}}{L C} )
в. ( frac{q_{0}}{sqrt{L C}} )
c. ( frac{q_{0}}{L C}-1 )
D. ( frac{q_{0}}{L C}+1 )
12
879 1. If i = 12; 0<t<T then r.m.s. value of current is
72
(d) None of these
12
880 Compare a step-up transformer with a step-down transformer based on the number of loops in the primary and secondary coils. 12
881 The incorrect statement for L-R-C series
circuit is
A. The potential difference across the resistance and the appleid e.m.f. are always in same phase
B. The phase difference across inductive coil is ( 90^{circ} )
C. The phase difference between the potential difference across capacitor and potential difference across inductance is ( 90^{circ} )
D. The phase difference between potential difference across capacitor and potential difference across resistance is ( 90^{circ} )
12
882 The alternating current in a circular is
described by the graph as shown in
figure. The rms current obtained from
the graph would be
A ( cdot 1.4 mathrm{A} )
B. 2.2 A
( c cdot 1.6 A )
D. 2.6 A
12
883 2. In a transformer, the number of turns in the primary are 140
and that in the secondary are 280. If the current in primary
is 4 A, then that in the secondary is
(a) 4A
(b) 2 A
(c) 6A
(d) 10 A (AIEEE 2002)
12
884 38. A sinusoidal ac current flows through a resistor of resistanceR.
If the peak current is Ip, then the power dissipated is
(a) 1Rcos e
(b) IR
(d) – BR
WUL
A
2011
bediib
uoltolto
12
885 Which of the following combinations should be selected for better tuning of an L-C-R circuit used for
communication?
A. ( R=20 Omega, L=1.5 mathrm{H}, mathrm{C}=35 mu F )
B. ( R=25 Omega, L=2.5 mathrm{H}, mathrm{C}=40 mu F )
c. ( R=15 Omega, L=3.5 mathrm{H}, mathrm{C}=30 mu F )
D. ( R=25 Omega, L=1.5 mathrm{H}, mathrm{C}=45 mu F )
12
886 In an L-C-R series circuit, at resonance
A. the current and voltage are in phase
B. the impedance is maximum
c. the current is minimum
D. the quality factor is Independent of R
E ( cdot ) the current leads the voltage by ( frac{pi}{2} )
12
887 A step-down transformer with an efficiency of ( 80 % ) is used on a 1000 v line to deliver ( 10 mathrm{A} ) at ( 100 mathrm{V} ) at the
secondary coil. The Current drawn from the line is
A . ( 1.5 mathrm{A} )
B. 2 A
( c cdot 3 A )
D. 1.25 A
E. 1 A
12
888 An ( L-C-R ) series circuit with ( L= )
( 0.120 H, R=240 Omega, ) and ( C=7.30 mu F )
carries an rms current of ( 0.450 A ) with a
frequency of ( 400 H z . ) What is the average rate at which electrical energy is dissipated (converted to other forms) in the inductor?
12
889 26. An LCR circuit is equivalent to
a damped pendulum. In an LCR
circuit the capacitor is charged to go
and then connected to the Land R as
shown below:
If a student plots graphs of the square of maximum
charge (Q Max) on the capacitor with time (t) for two
different values L, and L2 (L,>L) of L then which of the
following represents this graph correctly?
(Plots are schematic and not drawn to scale)
Oʻmax!
gmax
(a)
24 (b)
max
max
Q (for both L
and L)
(JEE Main 2015)
12
890 The peak voltage of an ac supply is ( 300 V . ) What is the rms voltage? 12
891 Power consumed in an AC circuit
becomes zero if
A. inductance and resistance are both high.
B. inductance and resistance are both low.
C. inductance is very high and resistance is negligible.
D. inductance is low and resistance is high.
12
892 In the given figure, the instantaneous
value of the alternating e.m.f is ( e= )
14.14sinwt. The voltmeter reading in
volts will be:
( mathbf{A} cdot 141.4 )
B. 10
c. 200.0
D. 70.7
12
893 What is ( Q ) factor of a RC circuit?
A ( cdot frac{1}{R} )
в. ( frac{X_{C}}{R} )
( c .1 )
D.
12
894 20. A 50 W, 100 V lamp is to be connected to an ac mains
of 200 V, 50 Hz. What capacitor is essential to be put in
series with the lamp?
(6)
30
tv5UF
100
(c)
uF
12
895 The secondary windings of a transformer in which the voltage is stepped down are usually made of thicker wire than the primary. Explain why. 12
896 The ratio of turns in the transformer is
given as ( 2: 3 . ) If the current passing through the primary coil is 3 A. Find the current through the load resistance:
A. ( 4.5 mathrm{A} )
B. 1.5 A
( c cdot 2 A )
D. 1 A
12
897 In which of the following circuit, there
may be no change in current with
increase in the frequency when same ac
current is passed through them:
( A )
B.
(b)
( c )
D.
12
898 A resistance of ( 10 Omega ) and an inductance
of ( 100 m H ) are connected in series with
an AC source of voltage ( boldsymbol{V}= ) ( 100 cos (100 t) ) volt. The phase difference
between the voltage applied and the current flowing in the circuit will be
A . zero
в. ( frac{pi}{2} )
c.
D. ( pi )
12
899 In a transformer, the number of turns in
the primary coil is 140 and that in the secondary coil is ( 280 . ) If the current in the primary coil is ( 4 A ), then that in the secondary coil is
( A cdot 4 A )
B. 2 A
( c cdot 6 A )
D. 10 A
12
900 An electronic test circuit produced a
resonant curve of half power frequency points at ( 414 H z ) and ( 436 H z ). If ( Q ) factor
be ( 10, ) the resonant frequency of the circuit is:
A ( .220 H z )
B. ( 22 H z )
c. ( 2.2 H z )
D. ( 0.22 H z )
12
901 The circuit shown below acts as:
A. Tuned filter
B. Low pass filter
c. High pass filter
D. Rectifier
12
902 The phase relationships between the voltages across the inductor, the capacitor and the source. 12
903 The natural frequency of the circuit
shown in adjoining figure is
A ( cdot frac{1}{2 pi sqrt{L C}} )
в. ( frac{1}{2 pi sqrt{2 L C}} )
c. ( frac{2}{2 pi sqrt{L C}} )
D. zero
12
904 ( ln ) an ( L C ) circuit the capacitor has
maximum charge ( q_{0} . ) The value of ( left(frac{d I}{d t}right)_{max }, ) where ( I ) is current in the circuit and ( t ) is time, is
( ^{A} cdot frac{q_{0}}{L C} )
в. ( frac{q_{0}}{sqrt{L C}} )
c. ( frac{q_{0}}{L C}-1 )
D. ( frac{q_{0}}{L C}+1 )
12
905 In a step-up transformer, if ratio of truns of primary to secondary is 1: 10 and primary voltage is ( 230 V ). If the load
current is ( 2 A ), then the current in
primary is
A . ( 20 A )
в. ( 10 A )
( c . $ 2 A )
D. ( 1 A )
12
906 Draw the graphs showing variation of Inductive reactance and Capacitive
reactance with frequency of applied A.C
source.
12
907 The capacitor offers zero resistance to
A. D.C. only
B. A.C. & D.C.
c. A.C. only
D. neither A.C. nor D.C.
12
908 An AC source is connected to a purely resistive circuit. What is true of the
following
A. current leads ahead of voltage in Phase
B. current lags behind voltage in phase
c. current and voltage are in same Phase
D. any of the above may be true depending upon the value of resistance
12
909 The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an ac supply of ( 20 vee, 50 )
Hz. What will be the output of the secondary?
12
910 What is resonant electrical circuit?
What are its types? Find out an expression for resonant frequency for series L-C-R circuit.
12
911 In an RLC series circuit shown in figure,
the readings of voltmeters ( V_{1} ) and ( V_{2} )
are ( 100 mathrm{V} ) and ( 120 mathrm{V}, ) respectively. The
same voltage is ( 130 mathrm{V} ). For this situation, mark out the incorrect statement.
A. Voltage across resistor, inductor and capacitor are 50 ( vee, 50 sqrt{3} mathrm{V} ) and ( 120+50 sqrt{3} mathrm{V}, ) respectively
B. Voltage across resistor. inductor and capacitor are 50 V, ( 50 sqrt{3} ) V and ( 120-50 sqrt{3} ) V, respectively
c. Power factor of the circuit is ( 5 / 13 )
D. The circuit is capacitance in nature
12
912 If the values of inductance and
frequency in an AC circuit are 2 henry and ( frac{10^{3}}{2 pi} ) Hz respectively then the value of inductive reactance will be
A ( cdot frac{2 times 10^{3}}{pi} Omega )
B . ( 2 times 10^{2} Omega )
( c cdot 10^{3} Omega )
D. ( 2 times 10^{3} Omega )
12
913 In transformer, power of secondary
A. less than primary coil
B. more than primary coil
C. more in step up and less in step primary coil
D. same in both primary and secondary coil
12
914 The primary and secondary coils of a
transformer
have 50 and 1500 turns respectively. If
the
magnetic flux linked with the primary coil is
given by ( phi=phi_{0}+4 t, ) where ( phi ) is in
webers, tis
time in seconds and ( phi_{0} ) is a constant,
the output voltage across the secondary coil is:
A. 30 volts
B. 90 volts
c. 120 volts
D. 220 volts
12
915 V sin [ax + (14)
55. A current source sends a current I = 1, cos(ot). When
connected across an un-
known load, it gives a a
voltage output of V =
Load
Vo sin[ot +(Td/4)] across
that load. Then the
voltage across the cur-
rent source may be
brought in phase with the current through it by
(a) connecting an inductor in series with the load
(b) connecting a capacitor in series with the load
(c) connecting an inductor in parallel with the load
(d) connecting a capacitor in parallel with the load
12
916 A charged ( 30 mu mathrm{F} ) capacitor is connected
to a ( 27 mathrm{mH} ) inductor. What is the
angular frequency of free oscillations of the circuit?
12
917 10. Find out the current flown through the wire at t= – second.
(a) 4.5 Amp
(b) 4.573 Amp
(c) V2 Amp (d) 9 Amp
12
918 A fascinating behaviour of the series RLC circuit is the phenomenon of resonance.
a) Explain Resonance in an LCR circuit.
b) Draw a graphical representation of
variation of current amplitude ( i_{m} ) with
frequency ( omega )
c) What do you mean by sharpness of resonance? Explain it.
12
919 A inductance capacitance circuit is in
the state of resonance. if the ( C=0.1 mu F )
and ( boldsymbol{L}=mathbf{0 . 2 5} ) Henry. Neglecting ohmic resistance of circuit what is the
frequency of oscillations
A. ( 1007 mathrm{Hz} )
в. ( 100 mathrm{Hz} )
( mathrm{c} .109 mathrm{Hz} )
D. ( 500 H z )
12
920 51. In the shown AC circuit phase different between cur
I, and I, is
Xc
mm
R
Ein Rio
ton-1 X ₂ – X c
I
12
921 A pure resistance is connected as
shown in the figure. The phase difference between the voltage applied and the current flowing in it will be
A . zero
в. ( frac{pi}{2} )
( c cdot-frac{pi}{2} )
D. ( frac{pi}{4} )
12
922 In an ideal transformer turn ratio is 2: 3
If input voltage is ( 100 mathrm{V} / 60 mathrm{Hz} ), then
output voltage is
A . 150 V/90 нz ( z ) z
B. 150 V/40 нZ
c. ( 150 vee / 60 ) Н ( z )
D. 66.6 V/60 нz
12
923 An AC circuit contains a variable
inductor ( L, ) connected in series with a
light bulb of resistance ( R ) as shown
Assume that the resistance of the light bulb is independent of its temperature. Now it is desired to reduce the power of the light bulb to one fourth then
(frequency of ac source is ( frac{R}{2 pi L_{0}} ) wher
This question has multiple correct options
A. Power factor of the circuit should be reduced to half
B. Inductance of the circuit should be increased by a factor of ( sqrt{3} )
c. Impedance of the circuit should be increased by a factor of 4
D. R.M.S. current in the circuit should be reduced to half
12
924 In medium wave broadcast a radio can
be tuned in the frequency range 800 ( mathrm{kHz} ) to ( 1200 mathrm{kHz} ). In L-C circuit of this
radio effective inductance is ( 200 mu H )
what should be the range of the variable capacitor?
( A cdot 88 ) pF to 198 pF
B. 98 pF to 198 pF
C. 78 pF to 146 pF
D. 20 pF to 112 pF
12
925 A series LCR circuit consists of an
inductor L a capacitor ( C ) and a resistor ( R )
connected across a source of emf ( varepsilon= )
( varepsilon_{0} sin omega t . ) When ( omega L=frac{1}{omega C} ) the current in
the circuit is ( l_{0} ) and if angular frequency
of the source is changed to ( omega ) ‘, the
current in the circuit becomes ( frac{l_{0}}{2}, ) then
the value of ( left|boldsymbol{omega}^{prime} boldsymbol{L}-frac{mathbf{1}}{omega^{prime} boldsymbol{C}}right| ) is
( A )
B. ( sqrt{3} ) R
( c cdot sqrt{15} )
12
926 An LC circuit has ( L=5 mathrm{mH} ) and ( C=20 mu mathrm{F} )
( boldsymbol{v}=mathbf{5} times mathbf{1 0}^{-mathbf{3}} ) coswt is supplied.
is twice the resonant frequency. Find
the maximum charge stored in the
capacitor:
A. 66.6 nc
B. 11.3 nc
c. 23.2 nc
D. 33.3 nç
12
927 a
rms
1.TI
.UT
10. An ac source of angular frequency ois fed across a resistor
r and a capacitor C in series. The current registered is I.
If now the frequency of source is changed to 0/3 (but
maintaining the same voltage), the current in then circuit
is found to be halved. Calculate the ratio of reactance to
resistance at the original frequency o
(b) VE
d)
12
928 A circuit has a self-inductance of ( 1 boldsymbol{H} )
and carries a current of ( 2 A . ) To prevent sparking, when the circuit is switched off, a capacitor which can withstand
( 400 V ) is used. The least capacitance of
the capacitor connected across the
switch must be equal to
A. ( 50 mu F )
B. ( 25 mu F )
c. ( 100 mu F )
D. ( 12.5 mu F )
12
929 ( mathbf{A} mathbf{7} mathbf{5} mathbf{0} boldsymbol{H} boldsymbol{z}, mathbf{2 0} boldsymbol{V} ) source is connected to
a resistance of ( 100 Omega, ) an inductance of
( 0.1803 H ) and a capacitance of ( 10 mu F )
all in series. The time in which the
resistance (thermal capacity ( left.=2 J /^{0} Cright) )
will get heated by ( 10^{0} C ) is
A . 348 s
B. 328 s
c. 248 s
D. 228
12
930 In a series ( L C R ) circuit the frequency of
a ( 10 V, A C ) voltage source id adjusted in such a fashion that the reluctance of
the inductor or measures ( 15 Omega ) and that
of the capacitor ( 11 Omega . ) If ( R=3 Omega, ) the
potential difference across the series combination of ( L ) and ( C ) will be:
( A cdot 8 V )
B. ( 10 V )
( c cdot 22 V )
D. ( 52 V )
12
931 A current of ( 5 A ) is flowing at ( 220 V ) in the primary coil of a transformer. If the voltage produced in the secondary coil
is ( 2200 V ) and ( 50 % ) of power is lost, then
the current in the secondary will be
A . ( 2.5 A )
в. ( 0.5 A )
c. ( 0.25 A )
D. ( 5 A )
12
932 A sinusoidal voltage of peak value ( 293 mathrm{V} ) and frequency ( 50 mathrm{Hz} ) is applied to a series LCR circuit in which ( mathrm{R}=6 Omega, mathrm{L} )
( =25 mathrm{mH} ) and ( mathrm{C}=750 mu mathrm{F} ). The impedance
of the circuit is:
A. ( 7.0 Omega )
B. ( 8.9 Omega )
( c cdot 9.9 Omega )
D. 10.0 ( Omega )
12
933 An oscillating circuit contains an inductor of inductance ( 10^{-6} mathrm{H} ) and two
capacitor each of capacitance ( 5 times 10^{-6} )
farad connected in parallel. Then the
resonance frequency of the circuit is
A ( cdot frac{10^{5}}{2 pi} )
B. ( frac{10^{5}}{pi} )
c. ( frac{3 times 10^{5}}{2 pi} )
D. ( frac{sqrt{2 times 10^{5}}}{pi} )
12
934 A step down transformer is connected
to 2400 volts line and 80 amperes of current is found to flow in output load.
The ratio of the turns in primary and secondary coil is ( 20: 1 . ) If the
transformer efficiency is ( 100 % ), then the current flowing in the primary coil will be
( mathbf{A} cdot 1600 mathrm{amp} )
B. 20 amp
c. 4 amp
D. 1.5 amp
12
935 ( ln ) an ( A C ) circuit voltage ( V=V_{0} sin w t )
and inductor L is connected across the
circuit. Then the instentaneous power
will be
A ( cdot frac{V_{0}^{2}}{2 w l} sin w t )
B. ( frac{-V_{0}^{2}}{2 w l} sin w t )
c. ( frac{V_{0}^{2}}{2 w l} sin 2 w t )
D. ( frac{V_{0}^{2}}{w l} sin w t )
12
936 The transformation ratio of a
transformer is ( 10: 1 . ) The current in the
primary circuit if the secondary current required is 100 A assuming the transformer be ideal, is
( A cdot 500 A )
B. 200 A
( c cdot 1000 A )
D. 2000 A
12
937 The capacitance in an oscillatory LC circuit is increased by ( 1 % ). The change in inductance required to restore its frequency of oscillation is to
A. decrease it by 0.5%
B. increase it by 1%
c. decrease it by 1%
D. decrease it by ( 2 % )
12
938 In a series LCR circuit ( boldsymbol{R}=mathbf{3 0 0 Omega}, boldsymbol{L}= )
( mathbf{0 . 9 H}, boldsymbol{C}=mathbf{2} boldsymbol{mu} boldsymbol{F}, boldsymbol{omega}=mathbf{1 0 0} mathbf{o} ) rad/s. The
impedance of the circuit is?
A. ( 500 Omega )
B. 1300Omega
c. ( 400 Omega )
D. ( 900 Omega )
12
939 20 V, 0.1 2 5.90
28. In the circuit of the figure, the source
frequency is a = 2000 rad s .
The current in the circuit will be
(a) 2 A
(b) 3.3
A
(c) 2/15 A
(d) V5 A
5 mH, 412
m
50 uF
12
940 In non-resonant circuit, the nature of
circuit for frequencies greater than the
resonant frequency is :
A . resistive
B. capacitive
c. inductive
D. both 1 and 2
12
941 A transformer having 4000 turns on its primary side and 500 turns on the secondary side. If the input voltage is
( 240 V, ) find out the output voltage of the secondary side of the transformer?
A . ( 15 ~ V )
в. ( 30 V )
c. ( 60 V )
D. ( 120 V )
E . ( 240 mathrm{V} )
12
942 The voltage across the capacitor as a
function of time is given by ( 10^{x} t^{2} V )
then find ( x )
A. 7
B. 6
( c cdot-5 )
D. 4
12
943 The number of turns in the coil of an AC
generator is 5000 and the area of the
coil is0.25 ( m^{2} . ) The coil is rotated at the
rate of 100 cycles /sec in the magnetic field of ( 0.2 W / m^{2} . ) then the peak value will be :
A. ( 786 mathrm{kv} )
B. 178 kV
c. ( 157 mathrm{kv} )
D. 123 kv
12
944 Primary winding and secondary winding of a transformer has
100 and 300 turns respectively. If its
input power is ( 60 mathrm{W} ) then output power of the transformer will be
A . 240 ( w )
B. 180 ( w )
( c cdot 60 w )
D. 20 W
12
945 What are the values of the elements? 12
946 An inductor and resistor are connected
in series with an ac source. In this
circuit.
A. The current and the PD across the resistance lead the
PD across the inductance
B. The current and the PD across the resistance lag behind the PD across the inductance by an angle ( pi / 2 )
C. The current and the PD across the resistance lag behind the PD across the inductance by an angle ( pi )
D. The PD across the resistance lags behind the PD across the inductance by an angle ( pi / 2 ) but the current in resistance leads the PD across the inductance by ( pi / 2 )
12
947 A coil of inductive reactance ( 1 / sqrt{3} Omega ) and resistance ( 1 Omega ) is connected to
( 200 V, 50 H z ) A.C. supply. The time lag
between maximum voltage and current
is
A ( cdot frac{1}{600} s )
в. ( frac{1}{200} s )
c. ( frac{1}{300} s )
D. ( frac{1}{500} s )
12
948 A current source sends a current i ( = )
( i_{0} cos (omega t) . ) When connected across an
unknown load gives a voltage output of,
( boldsymbol{v}=boldsymbol{v}_{0} sin (omega t+boldsymbol{pi} / 4) ) across that load
Then voltage across the current source
may be brought in phase with the
current through it by
A. connecting an inductor in series with the load
B. connecting a capacitor in series with the load
C. connecting an inductor in parallel with the load
D. connecting a capacitor in parallel with the load.
12
949 In an AC circuit, electrical energy is consumed in
A .
B.
( c cdot R )
D. Land
12
950 If the frequency of the AC source connected across a series LCR circuit is
continuously in which the following is observed. Assume all other parameters
are kept the same.
A. rms current continously increases.
B. rms current remains constant
c. rms current first increases, reaches a maximum and then decrease
D. rms current first decreases, reached a minimum and then increases
12
951 Draw the graph of ( I_{r m s} rightarrow omega ) for an A.C.
L-C-R series circuit and hence explain
Q-factor.
12
952 Draw a labelled diagram of a step-up transformer and explain how it works. State two characteristics of the primary coil as compared to its secondary coil. 12
953 The power in series ( R L C ) -circuit with
( A C ) source is given by :
A. zero
B. ( V I sin phi )
c. ( V I )
D. ( V I cos phi )
12
954 In an ideal step-up transformer input voltage is ( 110 mathrm{V} ) and current flowing in the secondary is ( 10 mathrm{A} ), if transformation
ratio is ( 10, ) calculate output voltage,
current in primary input power and
output power.
12
955 If the phase difference between Alternating Voltage and Alternating
Current is ( frac{pi}{6} ) and the resistance in the circuit is ( sqrt{300} Omega, ) then the impedance of the circuit will be
A . 25Omega
B. ( 50 Omega )
( c cdot 20 Omega )
D. ( 100 Omega )
12
956 A transformer consisting of 300 turns in the primary and 150 turns in the
secondary gives output power of ( 2.2 k W ) .f the current in the secondary coil is
( mathbf{1 0} A, ) then the input voltage and current in the primary coil are :
A . ( 220 V ) and ( 10 A )
B. ( 440 V ) and ( 5 A )
c. ( 440 V ) and ( 20 A )
D. 220V and 20A
12
957 A ( 50 H z ) alternating current of crest value ( 2.0 . A ) flows through the primary of a transformer. If the mutual inductance
between the primary and secondary is ( 0.25 H . ) The crest voltage induced in the
secondary is
A . ( 50 V )
B. ( 100 V )
c. ( 200 V )
D. 300V
12
958 toppr
Q Type your question_
( A )
B.
( c )
( D )
12
959 A coil has an inductance of ( 0.7 ~ H ) and is
joined in series with a resistance of
220Omega. When an alternating emf of ( 220 V ) at ( 50 ~ c p s ) is applied to it, then the
wattless component of the current in the circuit is (take ( 0.7 pi=2.2) )
( mathbf{A} cdot 5 A )
B. ( 0.5 A )
( mathbf{c} cdot 0.7 A )
D. ( 7 A )
12
960 ( ln ) a ( L C ) circuit. Angular frequency at resonance is ( boldsymbol{w} ). What will be the new
angular frequency when inductor’s
introduces is made 2 times and
capacitance is made 4 times?
A ( cdot frac{w}{sqrt{2}} )
в. ( frac{w}{2 sqrt{2}} )
c. ( 2 w )
D. ( frac{2 w}{sqrt{2}} )
12
961 Determine the voltage across the
inductor as a function of time(in ( mathrm{mV} ) )
12
962 After the capacitor gets fully charged,
( mathbf{S}_{1} ) is opened and ( mathbf{S}_{2} ) is closed so that the
inductor is connected in series with the
capacitor. Then,
A ( . ) at ( t=0, ) energy stored in the circuit is purely in the form of magnetic energy
B. at any time ( t>0 ), current in the circuit is in the same
c. at ( t>0, ) there is no exchange of energy between the inductor and capacitor
D. at any time ( t>0 ), instantaneous current in the circuitt ( operatorname{may} mathrm{v} sqrt{frac{mathrm{c}}{mathrm{L}}} )
12
963 In series ( L-C-R ) circuit voltage drop
across resistance is ( 8 V, ) across
inductor is ( 6 V ) and across capacitor is
( mathbf{1 2} V ). Then
A. Voltage of the source will be leading in the circuit
B. Voltage drop across each element will be less than the applied voltage.
c. Power factor of the circuit will be ( 3 / 4 )
D. None of the above
12
964 A step down transformer is used on
( 1000 V ) line to deliver ( 20 A ) at ( 120 V ) at
the secondary coil. If the efficiency of
the transformer is ( 80 % ) the current
drawn from the line is
( mathbf{A} cdot 3 A )
в. 30 А
( mathbf{c} cdot 0.3 A )
D. 2.4 ( A )
12
965 The inductive reactance of a coil is
( 2500 Omega . ) On increasing it’s selfinductance to three times, the new inductive reactance will be:
A. ( 7500 Omega )
B. 2500Omega
c. ( 1225 Omega )
D. zero
12
966 For an ideal transformer:
A. Output power = Input power
B. Efficiency is ( 100 % )
C ( cdot frac{V_{s}}{V_{p}}=frac{I_{p}}{I_{s}} )
D. All of these
12
967 An AC circuit containing ( 80 m H )
inductor and a ( 60 mu F ) capacitor is in series with ( 15 Omega ) resistance. They are
connected to ( 230 V, 50 H z ) AC supply
What is the total average power absorbed by the circuit?
A . zero
B. 5 watt
c. 40 watt
D. 10 watt
12
968 ( ln ) an oscillating ( boldsymbol{L}-boldsymbol{C} ) circuit, the
maximum charge on the capacitor is ( Q ) The charge on the capacitor, when the energy is stored equally between the electric and magnetic field is:
A ( cdot frac{Q}{2} )
B. ( frac{Q}{sqrt{2}} )
c. ( frac{Q}{sqrt{3}} )
D. ( frac{Q}{3} )
12
969 If a capacitance ( C ) is connected in series with an inductor of inductance ( L )
then the angular frequency will be
A ( cdot sqrt{frac{1}{L C}} )
в. ( sqrt{frac{L}{C}} )
c. LC
D. ( sqrt{L C} )
12
970 60. In the circuit shown (figure), the coil has inductance and
resistance. When X is joined to Y, the time constant is t
during the growth of current.
When the steady state is reached, heat is produced in the
coil at a rate P. X is now joined to Z. After joining X and Z:
(a) The total heat produced in
the coil is PT
(b) The total heat produced in
the coil is 1/2 Pt
(c) The total heat produced in
the coil is 2PT
(d) The data given are not sufficient to reach a conclusion
12
971 What are resonating frequency for two circuits. 12
972 The frequency of oscillation of current in
the inductance is
A ( cdot frac{1}{3 sqrt{L C}} )
в. ( frac{1}{6 pi sqrt{L C}} )
c. ( frac{1}{sqrt{L C}} )
D. ( frac{1}{3 pi sqrt{L C}} )
12
973 A power (set up) transformer with an
1: 8 turn ratio has ( 60 H_{z}, 120 V ) across
the primary, the load in the secondary is ( 10^{4} Omega . ) The current in the secondary is
A . ( 96 A )
B. ( 0.96 A )
( mathbf{c} .9 .6 A )
D. 96 m ( A )
12
974 A resistor and an inductor are
connected to an ac supply of ( 120 mathrm{V} ) and ( mathbf{5 0} boldsymbol{H} z . ) The current in the circuit is ( mathbf{3} boldsymbol{A} )
If the power consumed in the circuit is ( 108 W, ) then the resistance in the
circuit is
A. ( 12 Omega )
в. ( 40 Omega )
c. ( sqrt{(52 times 28)} ),
D. ( 360 Omega )
12
975 The figure shows the graphical
variation of the reactance of a capacitor
with frequency of ac source

Find the capacitance of the capacitor

12
976 A ( 100 Omega ) resistor is connected to a
( 220 V, 50 H z ) AC supply. Find rms value
of current in the circuit and the net
power consumed for a complete cycle.
A. ( 2.20 A, 484 W )
в. ( 3.20 A, 564 W )
c. ( 1.60 A, 278 W )
D. ( 5.80 A, 646 W )
12
977 Statement ( (A): ) The reactance offered by an inductance in A.C. circuit decreases with the increase of ( A C )
frequency. Statement ( (mathrm{B}): ) The reactance offered
by a capacitor in AC circuit increases with the increase of AC frequency.
A. A is true but B is false
B. Both A and B are true
c. A is false but B is true
D. Both A and B are false
12
978 A capacitor of capacitance ( C ) has initial
charge ( Q_{0} ) is connected to a inductor of
inductance L as shown. Att = 0 switch S
is closed. Then the current though the
inductor when energy in the capacitor is
three times energy of inductor is
A ( cdot frac{Q_{0}}{2 sqrt{L C}} )
B. ( frac{Q_{0}}{sqrt{L C}} )
c. ( frac{2 Q_{0}}{sqrt{L C}} )
D. ( frac{Q_{0}}{4 sqrt{L C}} )
12
979 C
ome 5
5. In an LCR circuit, the capacitance is changed from to
2C. For the resonant frequency to remain unchanged, the
inductance should be changed from L to
(a) 4L
(b) 2L
(c) L/2
(d) L/4 (AIEEE 2004)
12
980 In a series LCR circuit,the inductive
reactance is twice the resistance and the capacitance reactance is ( frac{1}{3}^{r d} ) the
inductive reactance. The power factor of
the circuit is:
A . 0.5
B. 0.6
( c .0 .8 )
D.
12
981 In the following diagram, the value of
emf of A.C. source will be :
A . ( 40 V )
B . ( 40 sqrt{2} V )
c. ( frac{40}{sqrt{2}} V )
D. ( 160 V )
12
982 Draw a labelled diagram of a step-up transformer. Obtain the ratio of
secondary to primary voltage in terms of number of terns and current in the
two coil.
12
983 A ( 100 Omega ) resistor is connected to a
( 220 V, 50 H z A C ) supply. Find ( r m s ) value
of current in the circuit :
A . ( 1.10 A )
в. ( 2.20 A )
c. ( 3.30 A )
D. ( 4.40 A )
12
984 An ideal coil of ( 10 mathrm{H} ) is joined in series
with a resistance of ( 5 Omega & ) a battery of ( 5 V . ) Two seconds after the connection is
made, the current flowing in amperes in the circuit is:
A ( cdot e^{-1} )
В ( cdotleft(1-e^{-1}right) )
( mathbf{c} cdot 1-e )
D. ( e )
12
985 Assertion
The only element that dissipates energy in an ac circuit is the resistive element
Reason

There are no power losses associated
with pure capacitances and pure inductances in an ac circuit
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
c. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

12
986 Power dissipated in pure inductance will be
( ^{A} cdot frac{L I^{2}}{2} )
В ( cdot 2 L I^{2} )
c. ( frac{L I^{2}}{4} )
D. zero
12
987 The current in the shown circuit is found to be ( 4 sin left(314 t-frac{pi}{4}right) A . ) Find the value of inductance 12

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