**51. Inductance of coil**

(a) is unaffected by the supply frequency

(b) decreases with the increase in supply frequency

(c) increases with the increase in supply frequency

(d) becomes zero with the increase in supply frequency

Ans: c

**52. In any A.C. circuit always**

(a) apparent power is more than actual power

(b) reactive power is more than apparent power

(c) actual power is more than reactive power

(d) reactive power is more than actual power

**Ans: a**

**53. Which of the following circuit component opposes the change in the circuit voltage ?**

(a) Inductance

(b) Capacitance

(c) Conductance

(d) Resistance

**Ans: a**

**54. In a purely inductive circuit**

(a) actual power is zero

(b) reactive power is zero

(c) apparent power is zero

(d) none of above is zero

**Ans: a**

**55. Power factor of electric bulb is**

(a) zero

(b) lagging

(c) leading

(d) unity

**Ans: d**

**56. Pure inductive circuit takes power from the A.C. line when**

(a) applied voltage decreases but cur¬rent increases

(b) applied voltage increases but cur¬rent decreases

(c) both applied voltage and current increase

(d) both applied voltage and current decrease

**Ans: a**

**57. Time constant of a circuit is the time in seconds taken after the application of voltage to each**

(a) 25% of maximum value

(b) 50% of maximum value

(c) 63% of maximum value

(d) 90% of the maximum value

**Ans: c**

**58. Time constant of an inductive circuit**

(a) increases with increase of inductance and decrease of resistance

(b) increases with the increase of inductance and the increase of resistance

(c) increases with the decrease of inductance and decrease of resistance

(d) increases with decrease of inductance and increase of resistance

**Ans: a**

**59. Time constant of a capacitive circuit**

(a) increases with the decrease of capacitance and decrease of resistance

(b) increases with the decrease of capacitance and increase of resistance

(c) increases with the increase of capacitance and decrease of resistance

(d) increase with increase of capacitance and increase of resistance

**Ans: d**

**60. Magnitude of current at resonance in R-L-C circuit**

(a) depends upon the magnitude of R

(b) depends upon the magnitude of L

(c) depends upon the magnitude of C

(d) depends upon the magnitude of R, LandC

**Ans: a**

**61. In a R-L-C circuit**

(a) power is consumed in resistance and is equal to I R

(b) exchange of power takes place between inductor and supply line

(c) exchange of power takes place between capacitor and supply line

(d) exchange of power does not take place between resistance and the supply line

(e) all above are correct

**Ans: e**

**62. In R-L-C series resonant circuit magnitude of resonance frequency can be changed by changing the value of**

(a) R only

(b) L only

(c) C only

(d) L or C

(e) R,L or C

**Ans: d**

**63. In a series L-C circuit at the resonant frequency the**

(a) current is maximum

(b) current is minimum

(c) impedance is maximum

(d) voltage across C is minimum

**Ans: a**

**64. The time constant of a series R-C circuit is given by**

(a) R/C

(b) RC2

(c) RC

(d) R2C

**Ans: c**

**65. If resistance is 20 Q. and inductance is 27 in a R-L series circuit, then time constant of this circuit will be**

(a) 0.001 s

(b) 0.1 s

(c) 10 s

(d) 100 s

**Ans: b**

**66. Which of the following coil will have large resonant frequency ?**

(a) A coil with large resistance

(b) A coil with low resistance

(c) A coil with large distributed capacitance

(d) A coil with low distributed capacitance

**Ans: c**

**67. If a sinusoidal wave has frequency of 50 Hz with 30 A r.m.s. current which of the following equation represents this wave ?**

(a) 42.42 sin 3141

(b) 60 sin 25 t

(c) 30 sin 50 t

(d) 84.84 sin 25 t

**Ans: a**

**68. The safest value of current the human body can carry for more than 3 second is**

(a) 4 mA

(b) 9 mA

(c) 15 mA

(d) 25 mA

**Ans: b**

**69. A pure inductance connected across 250 V, 50 Hz supply consumes 100 W. This consumption can be attributed to**

(a) the big size of the inductor

(b) the reactance of the inductor

(c) the current flowing in the inductor

(d) the statement given is false

**Ans: d**

**70. The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA. The power drawn by the circuit is**

(a) 12 kW

(b) 22 kW

(c) 32 kW

(d) 64 kW

**Ans: c**

**71. The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of**

(a) iron loss in core

(b) skin effect

(c) increase in temperature

(d) capacitive effect between adjacent coil turns

**Ans: a**

**72. In an AC. circuit, a low value of kVAR compared with kW indicates**

(a) low efficiency

(b) high power factor

(c) unity power factor

(d) maximum load current

**Ans: b**

**73. In AC. circuits, laminated iron is invariably used in order to**

(a) reduce eddy current loss

(b) increase heat radiation

(c) make assembly cheap and easier

(d) reduce circuit permeability

**Ans: a**

**74. The ratio of active power to apparent power is known as factor.**

(a) demand

(b) load

(c) power

(d) form

**Ans: c**

**75. All definitions of power factor of a series R-L-C circuit are correct except**

(a) ratio of net reactance and impedance

(b) ratio of kW and kVA

(c) ratio of J and Z

(d) ratio of W and VA

**Ans: a**