Recommended MCQs - 116 Questions - Alternating

Current Contact Number: 9667591930 / 8527521718

Q1. Two sinusoidal voltages of the same frequency are Q4. In a heating arrangement, an alternating current
shown in the diagram. What is the frequency, and the having a peak value of 28 A is used. To produce the same
phase relationship between the voltages? heat energy, if the direct current is used, its magnitude
must be:
1. about 14 A
2. about 28 A
3. about 20 A
4. cannot say

Q5. The variation of EMF with time for four types of

generators are shown in the figures. Which amongst them
can be called AC voltage?

Phase lead of N over M

Frequency in Hz
in radians

(1) 0.4 –π/4

(2) 2.5 –π/2

(3) 2.5 +π/2

(4) 2.5 –π/4

Q2. A direct current of 5A is superimposed on an 1. (a) and (d)

alternating current I = 10sin ωt flowing through a wire. 2. (a), (b), (c), (d)
The effective value of the resulting current will be: 3. (a) and (b)
1. ( )A
15 4. only (a)
2

2. 5√3A Q6. An ac ammeter is used to measure current in a circuit.

3. 5√5A When a given direct current passes through the circuit, the
4. 15 A ac ammeter reads 6 A. When another alternating current
passes through the circuit, the ac ammeter reads 8 A. Then
Q3. find the reading of this ammeter, if dc and ac flow through
the circuit simultaneously.
Alternating current cannot be measured by D.C. ammeter because 1. 10√2 A
2. 14 A
(1) A.C. can not pas through D.C. Ammeter 3. 10 A
4. 15 A
(2) A. C. changes direction

(3) Average value of current for complete cycle is zero

Q7. A sinusoidal supply of frequency 10 Hz and r.m.s.
voltage 12 V is connected to a 2.1 μF capacitor. What is
(4) D.C. Ammeter will get damaged r.m.s. value of current?
1. 5.5 mA
2. 20 mA
3. 26 mA
4. 1.6 mA

Page: 1
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q8. A generator produces a voltage that is given by V = Q14. The output current versus time curve of a rectifier is
240 sin 120 t, where t is in seconds. The frequency and shown in the figure. The average value of output current
r.m.s. voltage are in this case is
(1) 60 Hz and 240 V
(2) 19 Hz and 120 V
(3) 19 Hz and 170 V
(4) 754 Hz and 70 V

Q9. A 44 mH inductor is connected to 220 V, 50 Hz ac

supply. The RMS value of the current in the circuit is:
1. 1.0 A
2. 15 A
(1) 0
3. 15.92 A
(2)
I0

4. 14.29 A 2

(3)
2I0

Q10. The peak value of an alternating e.m.f. (4) I π

E = E sin ωt is 10 volt and its frequency is 50 Hz. At a

0
0

time t = , the instantaneous value of the e.m.f. is

1

600s Q15. Match List I (expression for current) with list II

1. 1 volt (RMS value of current) and select the correct answer.
2. 5√3 volt List I List II
3. 5 volt A. I = I sin ωt cos ωt (i) I
4. 10 volt
0 0

B. I = I sin (ωt + )
0
π

3
(ii) I /√2
0

Q11. An alternating current is given as i = i1 cos ωt - i2 sin

C. I = I (sin ωt + cos ωt) (iii) I e
0 0
ωt. The rms current is given by
1.
i1 + i2
D. I = I (e) 0 (iv) I /(2√2)
0

√2

| i1 + i2 |
2. A B C D
√2

2
i + i
2
(1) 4 2 1 3
3. √
1

2
2
(2) 4 2 3 1
(3) 2 4 3 1
(4) 2 4 1 3
2 2
i + i

4. √
1 2

√2

Q12. The RMS value of an alternating voltage given by

E = (6 sin ωt − 2 cos ωt) volt is Q16. A resistance of 20 ohms is connected to a source of
1. 4√2 V
an alternating potential V = 220 sin(100πt). The time
taken by the current to change from its peak value to r.m.s
2. 2√5 V
value is
3. 2√3 V (1) 0.2 sec
4. 4 V
(2) 0.25 sec
(3) 25 × 10–3 sec
Q13. The time required for a 50 Hz sinusoidal alternating (4) 2.5 × 10–3 sec
current to change its value from zero to the r.m.s. value
1. 1. 5 × 10 s −2

Q17. In an ac circuit I= 100 sin 200 πt. The time required

2. 2. 5 × 10 s −3
for the current to achieve its peak value will be:
3. 10 s−1

1. 1
sec
4. 10 s−6 100

2. sec
200
1

3. 300
1
sec

4. 1

400
sec

Page: 2
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q18. The r.m.s. value of potential difference V shown Q23. L, C and R represent physical quantities inductance,
in the figure is : capacitance and resistance respectively. The combination
representing dimension of frequency is
(1) LC
(2) (LC)–1/2
−1/2

(3) ( L
)
C

(4) C

Q24. In a LCR series network,

1. V 0
/√3 VL = 40 V, VC = 20 V and VR = 15 V . The supply
2. V 0 voltage is
3. V 0/
√2 1. 25V
4. V 0
/2 2. 75V
3. 35V
Q19. An alternating voltage (in volts) given by 4. Zero
V = 200√2sin100t is connected to 1 μF capacitor
through an ac ammeter. The reading of the ammeter will Q25. In an LCR circuit, the potential difference between
be the terminals of the inductance is 60 V, between the
1. 10 mA terminals of the capacitor is 30V and that between the
2. 20 mA terminals of resistance is 40V. The supply voltage will be
3. 40 mA equal to:
43. 80 mA (1) 50 V
(2) 70 V
Q20. An alternating current of frequency ‘f’ is flowing in (3) 130 V
a circuit containing a resistance R and a choke L in series. (4) 10 V
The impedance of this circuit is
(1) R + 2πfL Q26. In a series LCR circuit, resistance R = 10Ω and the
impedance Z = 20Ω. The phase difference between the
(2) √R + 4π f L 2 2 2 2

current and the voltage is

(3) √R + L 2 2

(1) 30°
(4) √R + 2πf L 2
(2) 45°
(3) 60°
Q21. A 100 Ω resistor is connected to a 220 V, 50 Hz ac (4) 90°
supply. The net power consumed over a full cycle is:
1. 484 W Q27. A series AC circuit has a resistance of 4Ω and an
2. 848 W inductor of reactance 3Ω . The impendance of the circuit
3. 400 W is z . Now a capacitor of reactance 6Ω is connected in the
1

4. 786 W series of above combination, the impedance becomes z , 2

z1
Then will be
z2

1. 1 : 1
Q22. In the circuit shown below, what will be the readings 2. 5 : 4
of the voltmeter and ammeter? 3. 4 : 5
4. 2 : 1

Q28. What is the Q-value of a series LCR circuit with L =

2.0 H, C = 32 µF and R = 10 Ω?
1. 35
2. 20
3. 15
4. 25
(1) 800 V, 2A
(2) 300 V, 2A
(3) 220 V, 2.2 A
(4) 100 V, 2A
Page: 3
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q29. In the circuit shown in the figure, neglecting source Q33. In a series RLC circuit, potential differences across
resistance, the voltmeter and ammeter reading respectively R, L and C are 30 V, 60 V and 100 V respectively as
will be: shown in figure. The e.m.f. of source (in volts) is

(1) 0V, 3A
(2) 150V, 3A
(3) 150V, 6A 1. 190
(4) 0V, 8A 2. 70
3. 50
Q30. An ideal resistance R, ideal inductance L, ideal 4. 40
capacitance C, and AC voltmeters V , V , V and V
1 2 3 4

are connected to an AC source as shown. At resonance: Q34. A resistance of 300 Ω and an inductance of henry 1

are connected in series to a ac voltage of 20 volts and 200

Hz frequency. The phase angle between the voltage and
current is :
(1) tan −1 4

(2) tan −1 3

(3) tan −1 3

(4) tan −1 2

1. Reading in V3 = Reading in V1
Q35. In an ac circuit, a resistance of R ohm is connected
2. Reading in V1 = Reading in V2
in series with an inductance L. If phase angle between
3. Reading in V2 = Reading in V4
voltage and current be 45°, the value of inductive
4. Reading in V2 = Reading in V3
reactance will be
(1) R

Q31. It is found that current through the LCR series circuit 4

is maximum. If V , V and V are potential differences (2)

R

r c L 2

across resistance, capacitor, and inductor respectively, (3) R

then which of the following is correct? (4) Cannot be found with the given data
1. Vr = VL > VC

2. VR ≠ VL = VC
Q36. The variation of the instantaneous current (I) and the
instantaneous emf (E) in a circuit is as shown in figure.
3. VR ≠ VL ≠ VC
Which of the following statements is correct?
4. VR = VC ≠ VL

Q32. A transistor-oscillator using a resonant circuit with

an inductance L (of negligible resistance) and a
capacitance C has a frequency f. If L is doubled and C is
changed to 4C, the frequency will be:
1. f/4
2. 8f
3. f/(2√2)
4. f/2 (1) The voltage lags behind the current by π/2.
(2) The voltage leads the current by π/2.
(3) The voltage and the current are in phase.
(4) The voltage leads the current by π.

Page: 4
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q37. For a series RLC circuit R = XL = 2XC. The Q43. An ac source of variable frequency f is connected to
impedance of the circuit and phase difference between V an LCR series circuit. Which one of the graphs in the
and i will be: figure represents the variation of the current I in the circuit
√5R with frequency f?
(1) , tan
2
(2)
−1

√5R
(2) 2
, tan
−1
(
1

2
)

(3) √5X C
, tan
−1
(2)

(4) √5R, tan

−1
(
1
)
2
(1)

Q38. For a LCR series circuit with an A.C. source of

angular frequency ω:
1. circuit will be capacitive if ω > 1

√LC

2. circuit will be inductive if ω = 1

√LC

3. power factor of circuit will be unity if capacitive (2)

reactance equals inductive reactance
4. current will be leading voltage if ω > 1

√LC

Q39. What is the value of inductance L for which

the current is a maximum in a series LCR
circuit with C=10 μF and ω = 1000s-1 ? (3)
1. 10 mH
2. 100mH
3. 1 mH
4. cannot be calculated unless R is known

Q40. In an LCR circuit having L = 8.0 henry, C = 0.5 μF (4)

and R = 100 ohm in series, the resonance frequency in
radian per second is: Q44. Voltage and current in an ac circuit are given by V=
(1) 600 radian π π
5 sin(100πt − ) V and l = 4 sin(100πt + ) A.
(2) 600 Hz 6 6

(3) 500 radian/sec Hence:

(4) 500 Hz 1. the voltage leads the current by 30°.
2. the current leads the voltage by 30°.
Q41. In a series, LC circuit, if L = 10 H and 3. the current leads the voltage by 60°.
−3

C = 3 × 10 F is connected to a 100 V-50 Hz a.c.

−7
4. the voltage leads the current by 60°.
source, the impedance of the circuit is:
5
Q45. In the circuit given below, the reading of the
1.
10
− 10π
3π voltmeter V will be
2. 0. 1π − 3 × 10 π −5

3. 10
−
3π
π

10

4. None of these

Q42. In series LCR circuit, the phase difference between

voltage across L and voltage across C is
1. Zero
2. π
3. π

2 1. 0
4. 2π 2. 100 V
3. 200 V
4. 300 V

Page: 5
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q46. A 50 Hz a.c. source of 20 volts is connected Q51. A coil of self-inductance L is connected in series
across R and C as shown in figure below. The with a bulb B and an AC source. The brightness of the
voltage across R is 12 volts. The voltage bulb decreases when
across C is – (1) frequency of the AC source is decreased
(2) the number of turns in the coil is reduced
(3) a capacitance of reactance Xc=XL is included in the
same circuit
(4) an iron rod is inserted in the coil
1. 8 V
2. 16V
3. 10 V
4. not possible to determine unless values of Q52. A series R-C circuit is connected to an alternating
R and C are given voltage source. Consider two situations:

Q47. An AC voltage is applied to a resistance R and an 1) When the capacitor is air-filled.

inductor L in series. If R and the inductive reactance are 2) When the capacitor is mica filled.
both equal to 3Ω, the phase difference between the applied Current through the resistor is I and voltage across the
voltage and the current in the circuit is capacitor is V then:
(1) π/4 1. V < V
a b

(2) π/2 2. V > V

a b

(3) zero 3. i > i

a b

(4) π/6 4. V = V
a b

Q48. In the circuit shown rms current is 11A. The Q53. The circuit is in a steady state when the key is at
potential difference across the inductor is:- position 1. If the switch is changed from position 1 to
position 2, then the steady current in the circuit is

E0
1.
R

1. 220 V 2.
E0

2. 0 V 3R

3. 300 V 3.
E0

2R
4. 200 V E0
4.
4R

Q49. In an L-C-R series AC circuit, the voltage across

each of the component L, C and R is 50 V. The voltage Q54. An ac source of angular frequency ω is fed across a
across the L-R combination will be resistor r and a capacitor C in series. The current
1. 50 V registered is I. If now the frequency of the source is
2. 50√2V changed to ω/3 (but maintaining the same voltage), the
3. 100 V current in the circuit is found to be halved. Calculate the
4. 0 V ratio of reactance to resistance at the original frequency ω.

(1) √
3

Q50. In a series LCR circuit, voltage leads the current 5

when: (2) √ 2

(Given that ω =resonant angular frequency)

5
0

1. ω < ω 0
(3) √ 1

2. ω = ω 0

(4) √
4

3. ω > ω 0 5

4. None of these
Page: 6
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q55. In a box Z of unknown elements (L or R any other Q58. The diagram shows a capacitor C and a resistor R
combination), an ac voltage E = E sin(ωt + ϕ) is connected in series to an ac source. V1 and V2 are
0

applied and current in the circuit was found to be voltmeters and A is an ammeter:
). Then the unknown elements in
π
I = I sin(ωt + ϕ +
0
4

the box maybe

Consider now the following statements

1. Only the capacitor I. Readings in A and V2 are always in phase
2. Inductor and resistor both II. Reading in V1 is ahead in phase with reading in V2
3. Either capacitor, resistor, and an inductor or only
III. Readings in A and V1 are always in phase
capacitor and resistor
4. Only the resistor Which of these statements is/are correct?
(1) I only
Q56. A 220 V, 50 Hz ac source is connected to an (2) II only
inductance of 0.2 H and a resistance of 20 ohms in series. (3) I and II only
What is the current in the circuit? (4) II and III only
1. 10A
2. 5A Q59. In a circuit L, C and R are connected in series with
3. 33.3A an alternating voltage source of frequency f. The current
4. 3.33A leads the voltage by 45°. The value of C is
(1) 1

2πf (2πf L+R)

(2) 1

Q57. A bulb is rated at 100 V, 100 W, and it's treated as a πf (2πf L+R)

resistor. The inductance of an inductor (choke coil) that (c) 1

2πf (2πf L−R)

should be connected in series with the bulb to operate the
(4) 1

bulb at its rated power with the help of an ac source of 200 πf (2πf L−R)

V and 50 Hz is
π
1. H
√3

2. 100 H

√2
3. H
π

√3
4. H
π

Page: 7
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q60. A constant voltage at different frequencies is applied Q62. A capacitor of capacitance 1 μF is charged to a
across a capacitance C as shown in the figure. potential of 1 V. It is connected in parallel to an inductor
of inductance 10 H. The maximum current that will flow
−3

in the circuit has the value

1. √1000 mA

2. 1 mA

3. 1 μF

4. 1000 mA

Q63. If q is the charge on the capacitor and i the current at

Which of the following graphs correctly depicts the time t, then voltage V will be:
variation of current with frequency?

(1)
q
1. L di

dt
+ iR −
C
= V
q
2. L di

dt
− iR +
C
= V
q
3. L
di
+ iR + = V
dt C
q
4. L
di
− iR − = V
(2)
dt C

Q64. When an ac source of e.m.f. e = E sin(100 t) is

0

connected across a circuit, and the phase difference

between the e.m.f. e and the current i in the circuit is
observed to be as shown in the diagram. If the circuit
π

consists possibly only of RC or LC in series, then the

(3) relationship between the two elements is given by:

(4)

Q61. The figure shows the variation of R, XL, and XC with (1) R = 1kΩ, C = 10μF
frequency f in a series L, C, R circuit. Then for what (2) R = 1kΩ, C = 1μF
frequency point, the circuit is inductive? (3) R = 1kΩ, L = 10H

(4) R = 1kΩ, L = 1H

Q65. An inductor (L) and resistance (R) are connected in

series with an AC source. The phase difference between
voltage (V) and current (i) is 45°. Now a capacitor (C) is
connected in series with L-R, if the phase difference
between V and i remains same, then capacitive reactance
and impedance of L-C-R circuit will be
(1) A 1. 2R, R√2
(2) B 2. R, R√2
(3) C 3. R, R
(4) All points
4. 2R, R√3
Page: 8
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q66. Which one of the following curves represents the Q69. One 10 V, 60 W bulb is to be connected to 100 V
variation of impedance (Z) with frequency f in a series line. The required induction coil has a self-inductance of
LCR circuit? value: (f = 50 Hz)
(1) 0.052 H
(2) 2.42 H
(3) 16.2 mH
(4) 1.62 mH
(1) Q70. Which of the following plots may represent the
reactance of a series LC combination?

(2)

(3) (1) a
(2) b
(3) c
(4) d

(4)

Q67. In the circuit shown below, the ac source has voltage

V = 20 cos(ωt) volts with ω = 2000 rad/sec. the
amplitude of the current will be nearest to

(1) 2A
(2) 3.3 A
(3) 2/√5A
(4) √5A

Q68. What is the reading of the a.c. voltmeter in the

network shown below?

1. zero
2. 100 V
3. 200 V
4. 500 V
Page: 9
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q71. The capacitor and a resistor are connected in series Q74. In the circuit shown in the figure, the AC source
across a.c supply. Which of the following phasor diagrams gives a voltage V = 20cos(2000t) volt. Neglecting source
may be correct? resistance, the voltmeter and ammeter readings will be
(approximately):

1. 2.

1. 4 V, 2.0 A
2. 0 V, 2 A
3. 0 V, 1.4 A
4. 8 V, 2.0 A

Q75. In the circuit shown, the AC source has voltage V =

20 cos(ωt) volt with ω= 2000 rad/s, the amplitude of the
current will be nearest to:

3. 4. 1. 2 A
2. 3.3 A
3. 2/√5 A
4. √5 A

Q76. A series LCR circuit containing 5.0 H inductor, 80

μF capacitor and 40 Ω resistor is connected to 230 V

variable frequency ac source. The angular frequencies of

the source at which power transferred to the circuit is half
the power at the resonant angular frequency are likely to
Q72. A coil has resistance 30 ohm and inductive be:
reactance 20 Ohm at 50 Hz frequency. If an ac 1. 46 rad/s and 54 rad/s
source, of 200 volts, 100 Hz, is connected across 2. 42 rad/s and 58 rad/s
the coil, the current in the coil will be 3. 25 rad/s and 75 rad/s
1. 2.0 A 4. 50 rad/s and 25 rad/s
2. 4.0 A
3. 8.0 A Q77. In an ac circuit, the current is given by
4. 20
A
i = 5 sin (100 t −
π
) and the ac potential is V = 200
√13
2

sin(100t) volt. Then the power consumption is :

Q73. The value of quality factor is : (1) 20 watts
1. ωL

R
(2) 40 watts
2. ω
(3) 1000 watts
RC
(4) 0 watt
3. √LC
4. L/R

Page: 10
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q78. The power factor of the given circuit is Q83. In an ac circuit, the current, i= 100sin100t A and
V=100sin(100t + π

3
) volt. Then the average power
dissipated in the ac circuit is:
1. 2500 W
2. 250 W
3. 5000 W
1.
1
4. 4000 W
2

1
2.
√2
Q84. In a series LCR circuit, the current through the ac
√3
source is 2 A. If resistor R has resistance 10 Ω, the
3.
2
average power dissipated in the circuit is:
4. 0
1. 20 W
2. 30 W
Q79. The power factor of a series LCR circuit in 3. 10 W
resonance condition is: 4. 40 W
1. zero

2.
1 Q85. In an L-R circuit, the inductive reactance is equal to
2
the resistance R of the circuit. An emf E = E0 cos (ωt) is
1
3.
√2
applied to the circuit. The power consumed in the circuit
is
4. 1 2
E

1. 0

Q80. A coil of inductive reactance 31 Ω has a resistance √2R

E
2

of 8 Ω. It is placed in series with a condenser of capacitive 2. 0

4R
reactance 25 Ω. The combination is connected to an a.c. E
2

source of 110 V. The power factor of the circuit is: 3. 2R

0

1. 0.56 E
2

4.
0

2. 0.64 8R

3. 0.80
4. 0.33 Q86. A circuit consists of 3 ohm resistance and 4 ohm
reactance. The power factor of the circuit is :
Q81. An inductor of inductance L and resistor of (1) 0.4
resistance R are joined in series and connected by a source (2) 0.6
of frequency ω. The power dissipated in the circuit is : (3) 0.8
2
(R +ω L )
2 2
(4) 1.0
(1) V

Q87. The instantaneous values of alternating current and

2

(2)
V R

2 2 2
(R +ω L )
voltages in a circuit are given as
(3) 2
V

2 2
1
(R +ω L ) i = sin(100 πt) ampere
√2
√R2 +ω2 L2
(4) 2
1
V e = sin(100πt + π/3) volt
√2

Q82. The potential differences across the resistance, The average power in Watts consumed in the circuit is :
capacitance and inductance are 80V, 40Vand 100V
√3
1. 4
respectively in an L-C-R circuit. The power factor of this
2. 1

circuit is 2

(1) 0.4 3. 1

(2) 0.5 4. 1

(3) 0.8 4

(4) 1.0

Page: 11
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q88. Q91. A resistance 'R' draws power 'P' when connected to

Power dissipated in an L-C-R series circuit connected to an AC source. If an inductance is now placed in series
an AC source of emf E is: with the resistance, such that the impedance of the circuit
becomes 'Z' the power drawn will be:
2
R
1. P ( )
Z

1. R
2. P √
Z

R
3. P ( )
Z

2. 4. P

3.

Q92. If R and L are resistance and inductance of a choke

coil and f is the frequency of current through it, then the
average power of the choke coil is proportional to:
4. 1. R
1
2.
2
f

1
3.
2
L

4. All of these

Q89. An L-C-R series circuit with 100 Ω resistance is

connected to AC source of 200 V and angular frequency Q93. The instanteneous power of resistor having
300 rad/s. When only the capacitance is removed, the resistance R across ac supply of E = E sin ωt is
2
0

current lags behind the voltage by 60°. When only the 1. E0

sin ωt
2

inductance is removed, the current leads the voltage by R

60°. Calculate the power dissipated in the L-C-R circuit.

E0
2
2. cos ωt
R
1. 200 W 2
E0
2. 400 W 3.
R
3. 300 W
4. zero
4. Zero
Q94. An inductor 20 mH, a capacitor 100 μF, and a
Q90. A series LCR circuit is connected to an ac voltage resistor 50 Ω are connected in series across a source of
source. When L is removed from the circuit, the phase emf, V= 10sin314t. The power loss in the circuit is:
difference between current and voltage is . If instead C
π

3 1. 0.79 W
is removed from the circuit, the phase difference is again 2. 0.43 W
π

3
between current and voltage. The power factor of the 3. 2.74 W
circuit is: 4. 1.13 W
1. 0.5
2. 1.0 Q95. The power factor of a good choke coil is:
3. −1. 0 (1) Nearly zero
4. Zero (2) Exactly zero
(3) Nearly one
(4) Exactly one

Page: 12
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q96. An inductor 20 mH, a capacitor 50μF, and a resistor Q101. In which of the following circuits, the power factor
40Ω are connected in series across a source of emf can be zero?
V=10sin340t. The power loss in the AC circuit is: 1. LC circuit
2. LCR circuit
1. 0.67 W 3. Purely resistive circuit
2. 0.78W 4. Both (1) & (2)
3. 0.89 W
4. 0.46 W Q102. The value of power factor for a parallel LC circuit
at a frequency less than resonance frequency is
Q97. LC oscillations are not sustainable for long due to 1. Zero
the following reason: 2. 1
1. Every inductor has some resistance. 3. > 1
2. The effect of resistance is to introduce a damping effect 4.< 1
on the charge & current in the circuit and the oscillations
finally die away. Q103. An LC circuit contains an inductor (L=25 mH ) and
3. Even if the resistance is zero, the total energy of the capacitor (C=25 mF) with an initial charge Q . After what
0

system is radiated away from the system in the form of time will the circuit have an equal amount of electrical
electromagnetic radiation. and magnetic energy?
4. All of the above 1.
π

160
s

3π
2. s
Q98. The natural frequency of the circuit shown in the 160
5π

figure is 3.
160
s

4. All of these

Q104. A condenser of capicity C is charged to a potential

difference of V1. 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 V2 is -
(1) 1

C(V
2
−V
2
)
2π√LC
1.
1 2

(2)
1
L
2 2
π√LC C(V +V )

2. 1 2

(3) 2
L

π√LC 1/2
2 2
C(V −V )
(4) None of these 3. ( 1 2
)
L

1/2
Q99. In LC oscillation, the current in the circuit when the C ( V1 −V2 )
2

4. ( )
total energy is stored in the form of magnetic energy is- L

(where q0 is maximum charge stored by capacitor)

1. Zero Q105. The primary and secondary coils of a transformer

2.
q0
have 50 and 1500 turns respectively. If the magnetic flux
ϕ linked with the primary coils is given by ϕ = ϕ + 4t,
√Lc
0
q0
3.
LC
where ϕ is in webers, t is time in second and ϕ is a 0

constant, the output voltage across the secondary coil is

4. q0 √LC
1. 120 V
2. 220 V
Q100. In an ideal parallel LC circuit, the capacitor 3. 30 V
is charged by connecting it to a dc source 4. 90 V
which is then disconnected. The current in the
circuit :-
1. becomes zero instantaneously.
2. grows monotonically.
3. decays monotonically.
4. oscillates instantaneously.
Page: 13
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q106. The primary winding of transformer has 500 turns Q111. In the transformer shown in figure, ratio of number
whereas its secondary has 5000 turns. The primary is of turns of primary to the secondary is
N1
=
1
. If a
connected to an ac supply of 20 V, 50 Hz. The secondary N2 50

will have an output of voltage souce of 10 V is connected across primary, then

(1) 200 V, 50 Hz induced current through the load of 10 kΩ in secondary
(2) 2 V, 50 Hz is-
(3) 200 V, 500 Hz
(4) 2 V, 5 Hz

Q107.

A step –down transformer transforms a supply line

voltage of 2200 volt into 220 volt. The primary coil
has 5000 turns. The efficiency and power transmitted
by the transformer are 90% and 8 kilowatt 1. A
1

20

respectively. Then the number of turns in the 2. zero

secondary is: 3. A
1

10

1. 5000 4. 1

5
A

2. 50 Q112. A transformer has an efficiency of 90% is working

on 200 V and 3 kW power supply. If the current in the
3. 500 secondary coil is 6 A the voltage across the secondary coil
and the current in the primary coil respectively are:
4. 5 1. 300 V, 15 A
2. 450 V, 15 A
3. 450 V, 13.5 A
4. 600 V, 15 A
Q108. In a step-up transformer, the turn ratio is 1: 20. The
resistance of 100 Ω connected across the secondary is Q113. In a transformer, the number of turns in the primary
drawing a current of 2A. The primary voltage and the and the secondary are 410 and 1230 respectively. If the
current respectively are current in the primary is 6A, then that in the secondary
1. 100 V, 0.5 A coil is:
2. 200 V, 10 A 1. 2 A
3. 10 V, 40 A 2. 18 A
4. 10 v, 20 A 3. 12 A
4. 1 A
Q109. The core of a transformer is laminated because :
1. energy losses due to eddy currents may be minimized Q114. A 220 V input is supplied to a transformer. The
2. the weight of the transformer may be reduced output circuit draws a current of 2.0 A at 440 V. If the
3. rusting of the core may be prevented efficiency of the transformer is 80%, the current drawn by
4. ratio of voltage in primary and secondary may be the primary windings of the transformer is:
increased 1. 3.6 A
2. 2.8 A
Q110. A step-down transformer is connected to 2400 volts 3. 2.5 A
line and 80 amperes of current is found to flow in output 4. 5.0 A
load. The ratio of the turns in primary and secondary coil
is 20 : 1. If transformer efficiency is 100%, then the Q115. In a step-up transformer, the turn ratio is 1:2. A
current flowing in primary coil will be Leclanche cell (e.m.f. 1.5V) is connected across the
(1) 1600 A primary coil. The voltage developed in the secondary coil
(2) 20 A would be-
(3) 4 A 1. 3.0 V
(4) 1.5 A 2. 0.75 V
3. 1.5 V
4. Zero

Page: 14
 Recommended MCQs - 116 Questions - Alternating
Current Contact Number: 9667591930 / 8527521718

Q116. Turn ratio of a step-up transformer is 1 : 25. If

current in load coil is 2A, then the current in primary coil
will be :
1. 25A
2. 50A
3. 0.25A
4. 0.5A

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1. (2) 2. (2) 3. (3) 4. (3) 5. (2) 6. (3)

7. (4) 8. (3) 9. (3) 10. (3) 11. (3) 12. (2)
13. (2) 14. (3) 15. (1) 16. (4) 17. (4) 18. (3)
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31. (2) 32. (3) 33. (3) 34. (1) 35. (3) 36. (2)
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73. (1) 74. (3) 75. (1) 76. (1) 77. (4) 78. (2)
79. (4) 80. (3) 81. (2) 82. (3) 83. (1) 84. (4)
85. (2) 86. (2) 87. (3) 88. (1) 89. (2) 90. (2)
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103. (4) 104. (3) 105. (1) 106. (1) 107. (3) 108. (3)
109. (1) 110. (3) 111. (1) 112. (2) 113. (1) 114. (4)
115. (4) 116. (2)

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