NEET

ALTERNATING CURRENT WS 1
NEET-UG - Physics

1. An inductor 20 mH, a capacitor 100 μ F and a resistor 50Ω are connected in series across a source of emf, V = [4]
10sin 314t. The power loss in the circuit is:

a) 1.13 W b) 0.43 W

c) 0.79 W d) 2.74 W
2. A circuit has a resistance of 12 ohm and an impedance of 15 ohm. The power factor of the circuit will be [4]

a) 0 ⋅ 8 b) 1 ⋅ 125

c) 0 ⋅ 4 d) 1 ⋅ 25

3. In an LCR-series a.c. circuit, the voltage across each of the components. L, C and R is 50 V. The voltage across [4]
the LC-combination will be:

a) zero b) 100 V
–
c) 50√2 V d) 50 V
4. In an ideal inductor, L = 4H and ω = 100 rad/s. The power developed is: [4]

a) 0 b) 2V0I0
Vo Io
c) V0I0 d) 2

5. Series LCR circuit is connected to a variable frequency 230 V source where L = 5.0 H, C = 80 μF, R = 40 Ω . [4]
Impedance of the circuit and the amplitude of current at the resonating frequency are

a) 50 Ω , 8.1 A b) 40 Ω , 5.75 A

c) 80 Ω , 3.9 A d) 25 Ω , 5.4 A
6. The power dissipated in an LCR series circuit connected to an a.c. source of emf ε is [4]
2

a) b)
2
ε R 1
2 2
ε [ √R +(Lω− ) ]
2 Cω
2 1
[ R +(Lω− ) ]
Cω
R

c) d)
2
ε R 1
2 2
ε √R +(Lω− )
2 Cω
2 1
√R +(Lω− )
Cω R

7. A transformer of 100% efficiency has 200 turns in the primary coil and 40000 turns in the secondary coil. It is [4]
connected to a 220 V main supply and secondary feeds to a 100 kΩ resistance. The potential difference per turn
is

a) 11 V b) 18 V

c) 25 V d) 1.1 V
8. A series circuit consists of an ac source of variable frequency, a 115.0 Ω resistor, a 1.25 μF capacitor, and a [4]
4.50-mH inductor. The impedance of this circuit when the angular frequency of the ac source is adjusted to half
the resonant angular frequency is

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 a) 156.0 Ω b) 166.0 Ω

c) 176.0 Ω d) 146.0 Ω
9. In a pure capacitive circuit, the current [4]

a) leads the applied emf by angle b) leads the applied emf by an angle π
π

c) and applied emf are in same phase d) lags behind the applied emf by angle
π

10. If the rms current in a 50 Hz ac circuit is 5 A, the value of the current 1

300
seconds after its value becomes zero is [4]
−
−
a) 5

6
A b) 5√
3
A
2

–
c) d)
5
A 5√2A
√2

11. An inductive circuit have zero resistance. When ac voltage is applied across this circuit, then the current lags [4]
behind the applied voltage by an angle

a) 90o b) 0o

c) 45o d) 30o

12. The voltage across a resistor, an inductor, and a capacitor connected in series to an ac source are 20 V, 15 V and [4]
30 V respectively. The resultant voltage in the circuit is

a) 5 V b) 25 V

c) 20 V d) 65 V
13. A condenser of 250 μ F is connected in parallel to a coil of inductance 0.16 mH, while its effective resistance is [4]
20 Ω . Determine the resonant frequency.

a) 8 × 105 Hz b) 9 × 10 Hz

c) 16 × 107 Hz d) 9 × 104Hz

14. A coil of inductance 0.50 H and resistance 100 Ω is connected to a 240 V, 50 Hz ac supply. Maximum current in [4]
the coil and time lag between the voltage maximum and the current maximum are

a) 1.62 A, 3.82 ms b) 2.82 A, 3.82 ms

c) 1.82 A, 3.2 ms d) 5.22 A, 2.82 ms

15. A 220 volt input is supplied to a transformer. The output circuit draws a current of 2.0 ampere at 440 volts. If the [4]
efficiency of the transformer is 80 %, the current drawn by the primary windings of the transformer is:

a) 2.5 ampere b) 5.0 ampere

c) 2.8 ampere d) 3.6 ampere

16. A coil has a resistance of 48.0 Ω . At a frequency of 80.0 Hz, the voltage across the coil leads the current in it by [4]
53
∘
. Inductance of the coil is

a) 0.114 H b) 0.84 H

c) 0.94 H d) 0.124 H
17. An ideal inductor is connected across an AC source of voltage. The current in the circuit [4]

a) lags voltage in phase by π. b) lags voltage in phase by .

π

c) is ahead of voltage in phase by π

2
. d) is ahead of the voltage in phase by π.

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18. In an a.c. circuit, the current flowing is I = 5 sin (100 t - ) (in A) and the potential difference is V = 200 sin 100 [4]
π

t (in V). The power consumption is equal to

a) 40 W b) 20 W

c) 0 W d) 1,000 W
19. The impedance of a series LCR circuit is [4]
−−−−−−−−−−−−
a) R + XL + XC b) 1
+
1
+ R
2
√ 2 2
X X
C L

−−−−−−−−−−−− −−−−−−−−−−−−−−
c) √X 3
L
− X
C
2 2
+ R d) √R2 + ( X
L − XC )
2

20. A resistor of 100 Ω and a capacitor of 10μF are connected in series to a 220 V 50 Hz ac source. Voltage across [4]
the resistor and capacitance are

a) 66 V, 210 V b) 66 V, 110 V

c) 60 V, 280 V d) 56 V, 210 V
21. In an electrical circuit, the components R, L, C and an ac voltage source are all connected in series. When L is [4]
removed from the circuit, the phase difference between the voltage and the current in the circuit is . If instead,
π

C is removed from the circuit, the phase difference is again . The power factor of the circuit is:
π

a) √3
b) 1

2
2

c) 1 d) 1

√2

22. A transmitting station transmits radiowaves of wavelength 360 m. Find the inductance of the coil required with a [4]
condenser of capacity 1.20 pF in the resonant circuit.

a) 3.07 × 10-8 H b) 2.25 × 10-8 H

c) 1.25 × 10-8 H d) 1.9 × 10-8 H

23. The selectivity of a series LCR a.c. circuit is large, when [4]

a) L is small and R is small b) L is large and R is small

c) L is large and R is large d) L = R

24. An inductor with L = 9.50 mH is connected across an ac source that has voltage amplitude 45.0 V. Phase angle [4]
for the source voltage relative to the current is

a) 120o b) 90o

c) -180o d) -90o

25. The phase difference between the current and the voltage in series LCR circuit at resonance is [4]

a) b)
π
π
2

c) π

3
d) zero
26. In the AC circuit, the current is expressed as I = 100 sin 200πt . In this circuit the current rises from zero to peak [4]
value in time:

a) 1

300
s b) 1

100
s

c) 1

400
s d) 1

200
s

27. The best material for the core of a transformer is: [4]

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 a) soft iron b) mild steel

c) hard steel d) stainless steel

28. A voltage signal is described by: [4]
v = V0 for 0 ≤ t ≤
T

= 0 for T

2
≤ t ≤ T

for a cycle. Its rms value is:

V0 V0
a) b)
2 √2

–
c) V0 d) √2 V0

29. A transformer is used to light a 100 watt and 110 volt lamp from a 220 volt mains. If the main current is 0.5 [4]
ampere, the efficiency of the transformer is approximately

a) 90% b) 30%

c) 20% d) 10%
30. The power factor of a series LCR circuit at resonance will be [4]

a) 1

2
b) 1

c) 0 d) 1

√2

31. What is the ratio of inductive and capacitive reactance in an ac citcuit? [4]

a) ω 2
LC b) LC2

c) ω d)
2 LC
L
2
ω

32. In an LRC series circuit R = 300.0 Ω , XC = 300.0 Ω and XL = 500.0 Ω . The average power consumed in the [4]

resistor is 60.0 W. What is the power factor of the circuit?

a) 0.881 b) 0.831

c) 0.931 d) 0.911
33. An electric bulb marked 40 W and 200 V is used in a circuit of supply voltage 100 V. Its power would be: [4]

a) 20 W b) 100 W

c) 10 W d) 40 W
34. The rms value of AC current which when passed through a resistor produces heat energy four times that [4]
produced by DC of 2 A through the same resistor in same time, is:

a) 32 A b) 8 A

c) 2 A d) 4 A
35. Parameter that remains unchanged in a transformer is [4]

a) frequency b) voltage

c) efficiency d) current
36. The wiring for a refrigerator contains a starter capacitor. A voltage of amplitude 170 V and frequency 60 Hz [4]
applied across the capacitor is to produce a current amplitude of 0.850 A through the capacitor. Capacitance
required is

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 a) 17.8 μF b) 13.3 μF

c) 15.3 μF d) 23.4 μF
37. A conductor of 10 Ω is connected across a 6 V ideal source. The power supplied by the source to the conductor [4]
is

a) 1.8 W b) 7.2 W

c) 2.4 W d) 3.6 W
38. The coil of a choke in a circuit [4]

a) has high resistance to d.c. circuit. b) increases the current

c) decreases the current d) does not change the current

39. A circuit is connected to an ac source of variable frequency. As the frequency of the source is increased, the [4]
current first increases and then decreases. Which of the following combinations of elements is likely to comprise
the circuit?

a) L and R b) L, C and R

c) L and C d) R and C
40. A 100 mH coil carries a current of 1 A. Energy stored in the form of the magnetic field is [4]

a) 1 J b) 0.1 J

c) 0.5 J d) 0.05 J
41. The best material for the core of a transformer is [4]

a) soft iron b) hard steel

c) mild steel d) stainless steel

42. A choke coil has [4]

a) high inductance and high resistance b) low inductance and high resistance

c) low inductance and low resistance d) high inductance and low resistance
43. An inductor may store energy in [4]

a) its magnetic field b) its electric field

c) both in electric and magnetic fields d) its coils

44. The rms current in a circuit connected to 50 Hz ac source is 15 A. The value of the current in the circuit ( 1
)s [4]
600

after the instant the current is zero, is

a) b)
15 √2
A A
√2 15

–
c) 15√2 A d) 8 A
45. In an LRC series circuit R = 300.0 Ω , XC = 300.0 Ω and XL = 500.0 Ω . The average power consumed in the [4]

resistor is 60.0 W. Rms voltage of the source is

a) 151 V b) 141 V

c) 161 V d) 131 V
46. Quantity that remains unchanged in a transformer is [4]

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 a) voltage b) Ampere

c) frequency d) current
47. If the current in a series LCR circuit is maximum, then ω will be: [4]
−−
−
a) as large as possible b) √LC

−−−−
c) √LC R d) equal to natural frequency of LCR system
48. The peak voltage of 220 V ac mains is [4]

a) 155.6 V b) 440 V

c) 220.0 V d) 311 V
49. A small signal voltage V(t) = V0 sin t is applied across an ideal capacitor C. [4]

a) Current I(t) lags voltage V(t) by 90o b) Current I(t) leads voltage V(t) by 180o.

c) Over a full cycle the capacitor C does not d) Current I(t) is in phase with voltage V(t)
consume any energy from the voltage
source.
50. A step down transformer is used on a 1000 V line to deliver 20 A at 120 V at the secondary coil. If the efficiency [4]
of the transformer is 80%, the current drawn from the line is

a) 3 A b) 30 A

c) 2.4 A d) 0.3 A
51. An ac voltage v = v0 sin ωt is applied to a series combination of a resistor R and an element X. The [4]
instantaneous current in the circuit is I = I0 sin (ωt + . Then which of the following is correct?
π
)
4

–
a) X is an inductor and XL = √2R b) X is an inductor and XL = R
–
c) X is a capacitor and XC = √2 R d) X is a capacitor and XC = R

52. Which of the following statements about a series LCR circuit connected to an ac source is correct? [4]

a) At resonance, the voltage drop across the b) At resonance, the voltage drop across the
inductor is more than that across the capacitor is more than that across the
capacitor. inductor.

c) If the net reactance (XL - XC) of circuit d) If the frequency of the source is increased,

becomes equal to its resistance, then the the impedance of the circuit first decreases
and then increases.
current leads the voltage by 45o.
53. The voltage across the terminals of an ac power supply varies with time according to Vcosωt . The voltage [4]
amplitude is V = 45.0 V. Average potential difference between the two terminals of the power supply is

a) 35.8 V b) 33.8 V

c) 37.8 V d) 0 V
54. The reactance of a capacitor of capacitance C connected to an ac source of frequency ω is X. If the capacitance [4]
of the capacitor is doubled and the frequency of the source is tripled, the reactance will become:

a) b) 6 X
3
X
2

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 c) X

6
d) 2

3
X

55. In a transformer, number of truns in the primary is 140 and that in the secondary is 280. If current in primary is 4 [4]
A, then that in the secondary is:

a) 6 A b) 10 A

c) 2 A d) 4 A
56. A series LCR circuit with R = 20 Ω , L = 1.5 H and C = 35 μF is connected to a variable-frequency 200 V ac [4]
supply. When the frequency of the supply equals the natural frequency of the circuit, average power transferred
to the circuit in one complete cycle is

a) 2800 W b) 2000 W

c) 1000 W d) 1800 W
–
57. In an ac circuit an alternating voltage, e = 200√2 sin 100t volts is connected to a capacitor of capacity 1 μ F. [4]
The rms value of the current in the circuit is

a) 20 mA b) 100 mA

c) 200 mA d) 10 mA
58. A circuit containing a 80 mH inductor and a 60 μF capacitor in series is connected to a 230 V, 50 Hz supply. [4]
The resistance of the circuit is negligible. Average powers transferred to the inductor and to the capacitor are
respectively

a) 10 W, 10 W b) 0 W, 0 W

c) 10 W, 20 W d) 20 W, 10 W
59. With increase in frequency of an A.C. supply, the impedance of a series L-C-R circuit [4]

a) remains constant b) decreases at first, becomes minimum and

then increases

c) increases d) decreases
60. The primary winding of a transformer has 500 turns, whereas its secondary has 5,000 turns. The primary is [4]
connected to an a.c. supply 20 V-50 Hz. The secondary will have an output of:

a) 200 V - 50 Hz b) 200 V - 500 Hz

c) 2 V - 50 Hz d) 2 V - 5 Hz
61. The peak value of an alternating emf ε given by ε = ε0 cos ωt is 10 volt and its frequency is 50 Hz. At time t = [4]
sec, the instantaneous emf is:
1

600

a) 10 V b) 5 V
–
c) 5√3 V d) 1 V
62. In a series LC circuit connected to an ac source, with the increase in the frequency of the source, the net [4]
reactance:

a) decreases linearly b) first increases to become maximum and

then decreases to zero

c) first decreases to become zero and then d) increases linearly

increases

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63. The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux ϕ [4]
linked with the primary coil is given by ϕ = ϕ0 + 4t , where ϕ is in weber, t is time in second and ϕ is a
0

constant, the output voltage across the secondary coil is:

a) 90 V b) 220 V

c) 120 V d) 30 V
64. In an ac circuit, voltage V and current i are given by [4]
V = 100 sin 100 t volt
i = 100 sin (100t + ) mA
π

The power dissipated in the circuit is

a) 5 W b) 10 W

c) 2.5 W d) 104W

65. When an alternating voltage E = E0 sin ωt is applied to a circuit, a current I = I0 sin(ωt + flows through it. [4]
π
)
2

The average power dissipated in the circuit is

E0 I0
a) Erms ⋅ Irms b)
√2

c) Zero d) E0 I0

66. Alternating current can not be measured by d.c. ammeter, because: [4]

a) average value of current of complete cycle b) a.c. cannot pass through a.c. ammeter
is zero

c) a.c. ammeter will get damaged d) a.c. changes direction

67. The primary winding of a transformer has 50 turns and its secondary has 500 turns. If the primary is connected [4]
to a.c. supply of 20 V-50 Hz, then secondary will have an

a) 200 V - 50 Hz b) 2 V - 5 Hz

c) 200 V - 500 Hz d) 2 V - 50 Hz
68. Inductance of an inductor whose reactance is 120 Ω at 80.0 Hz is [4]

a) 0.239 H b) 0.209 H

c) 0.199 H d) 0.219 H
69. An a.c. is represented by = 220sin(100)t V and is applied over resistance of 110 Ω . The heat produced in 7 min [4]
is:

a) 11 × 103 cal b) 25 × 103 cal

c) 33 × 103 cal d) 22 × 103 cal

70. A hair dryer meant for 110V, 60Hz is to be used in India. If 220 V is the supply voltage in India, the turns ratio [4]
for a transformer would be

a) step-down transformer with turn ratio 3 : 1 b) step-up transformer with turn ratio 1 : 2

c) step-down transformer with turn ratio 2 : 1 d) step-down transformer with turn ratio 2.5 : 1
71. In a series RLC circuit R = 300 Ω , L = 60 mH, C = 0.50 μF applied voltage V = 50 V and ω = 10,000 rad/s. [4]
Inductive reactance X , capacitive reactance X and impedance Z are
L C

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 a) 600 Ω , 200 Ω and 500Ω b) 450 Ω , 200 Ω and 450 Ω

c) 550 Ω , 300 Ω and 100 Ω d) 500 Ω , 250 Ω and 500 Ω

72. The power factor of an a.c. circuit having resistance R and inductance L (connected in series) and an angular [4]
velocity ω is:

a) R /(R2 + ω2L2)1/2 b) R / ωL

c) R /(R2 - ω2L2)1/2 d) ω L/R

73. The core of a transformer is laminated to reduce the effect of [4]

a) flux leakage b) hysteresis loss

c) eddy current d) copper loss

74. The phase difference between the alternating current and emf is . Which of the following cannot be the [4]
π

constituent of the circuit?

a) L alone b) C alone

c) L-C d) R, L
75. A step up transformer operates on a 230 volt line and a load current of 2 ampere. The ratio of the primary and [4]
secondary windings is 1 : 25. The current in the primary is:

a) 15 amp b) 25 amp

c) 12.5 amp d) 50 amp

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