a c fundamentals circuits and circuit theory MCQs – Page 2

Practise focused a c fundamentals circuits and circuit theory questions with marked answers for exam preparation and subject revision.

a c fundamentals circuits and circuit theory Mcqs

51. Time constant of an inductive circuit___________?
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A. increases with decrease of inductance and increase of resistance

B. increases with decrease of inductance and decrease of resistance

C. increases with increase of inductance and decrease of resistance

D. increases with the increase of inductance and the increase of resistance

52. A heater is rated as 230 V, 10 kW, A.C. The value 230 V refers to__________?
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A. average voltage

B. peak voltage

C. none of the above

D. r.m.s. voltage

53. Capacitive reactance is more when_______?
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A. capacitance is less and frequency of supply is more

B. capacitance is more and frequency of supply is less

C. capacitance is more and frequency of supply is more

D. capacitance is less and frequency of supply is less

54. Power factor of the system is kept high__________?
0

A. to reduce voltage regulation of the line

B. to maximise the utilization of the capacities of generators, lines and transformers

C. due to all above reasons

D. to reduce line losses

55. The period of a sine wave is _____ seconds. Its frequency is
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A. 20 Hz

B. 40 Hz

C. 50 Hz

D. 30 Hz

56. In the case of an unsymmetrical alternating current the average value must always be taken over__________?
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A. the whole cycle

B. unsymmetrical part of the wave form

C. the quarter cycle

D. the half cycle

57. Pure inductive circuit takes power from the A.C. line when_________?
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A. applied voltage decreases but current increases

B. applied voltage increases but current decreases

C. both applied voltage and current increase

D. both applied voltage and current decrease

58. In an A.C. circuit power is dissipated in____________?
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A. inductance only

B. none of the above

C. capacitance only

D. resistance only

59. Time constant of an inductive circuit_________?
0

A. increases with increase of inductance and decrease of resistance

B. increases with the decrease of inductance and decrease of resistance

C. increases with decrease of inductance and increase of resistance

D. increases with the increase of inductance and the increase of resistance

60. The power is measured in terms of decibles in case of_________?
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A. electronic equipment

B. transformers

C. current transformers

D. auto transformers

61. The inductance of a coil can be increased by_________?
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A. increasing core length

B. choosing core material having high relative permeability

C. decreasing the number of turns

D. decreasing the diameter of the former

62. In an AC. circuit, a low value of kVAR compared with kW indicates_________?
0

A. low efficiency

B. maximum load current

C. high power factor

D. unity power factor

63. In R-L-C series resonant circuit magnitude of resonance frequency can be changed by changing the value of__________?
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A. LorC

B. C only

C. L only

D. R only

E. R,LorC

64. In AC. circuits, laminated iron is invariably used in order to__________?
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A. increase heat radiation

B. make assembly cheap and easier

C. reduce circuit permeability

D. reduce eddy current loss

65. Inductance of coil___________?
0

A. becomes zero with the increase in supply frequency

B. increases with the increase in supply frequency

C. decreases with the increase in supply frequency

D. is unaffected by the supply frequency

66. The time constant of a series R-C circuit is given by____________?
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A. RC2

B. R/C

C. R2C

D. RC

67. In a parallel R-C circuit, the current always________the applied voltage?
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A. leads

B. lags

C. none of the above

D. remains in phase with

68. In a series L-C circuit at the resonant frequency the__________?
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A. impedance is maximum

B. current is maximum

C. voltage across C is minimum

D. current is minimum

69. The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of____________?
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A. increase in temperature

B. skin effect

C. capacitive effect between adjacent coil turns

D. iron loss in core

70. In a pure inductive circuit if the supply frequency is reduced to 1/2, the current will__________?
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A. be four times as high

B. be doubled

C. be reduced by half

D. be reduced to one fourth

71. The r.m.s. value of half wave rectified sine wave is 200 V. The r.m.s. value of full wave rectified AC. will be___________?
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A. 111 V

B. 141.4 V

C. 282.8 V

D. 100 V

72. If a sinusoidal wave has frequency of 50 Hz with 30 A r.m.s. current which of the following equation represents this wave_________ ?
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A. 84.84 sin 25 t

B. 60 sin 25 t

C. 30 sin 50 t

D. 42.42 sin 3141

73. Aphasoris________?
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A. a line which represents the magnitude and phase of an alternating quantity

B. an instrument used for measuring phases of an unbalanced 3-phase load

C. a line representing the magnitude and direction of an alternating quantity

D. a coloured tag or band for distinction between different phases of a 3-phase supply

74. A pure inductance connected across 250 V, 50 Hz supply consumes 100 W. This consumption can be attributed to_________?
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A. the current flowing in the inductor

B. the statement given is false

C. the big size of the inductor

D. the reactance of the inductor

75. The equation of 50 Hz current sine wave having r.m.s. value of 60 A is____________?
0

A. 60 sin 50 t

B. 60 sin 25 t

C. 84.84 sin 3141

D. 42.42 sin 314 t

76. Which of the following statements pertains to resistors only _____________?
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A. can act as energy storage devices

B. oppose sudden changes in voltage

C. can dissipate considerable amount of power

D. connecting them in parallel increases the total value

77. Which of the following refers to a parallel circuit ?
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A. The current through any one element is less than the source current

B. The equivalent resistance is greater than any one of the resistors

C. The voltage across element is in proportion to its resistance value

D. The current through each element is same

78. In a three-phase supply floating neutral is undesirable because it way give rise to___________?
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A. high voltage across the load

B. low voltage across the load

C. minimun voltage across the load

D. unequal line voltages across the load

79. Wire-wound resistors are unsuitable for use at high frequencies because they_______?
0

A. exhibit unwanted inductive and capacitive effects

B. create more electrical noise

C. consume more power

D. are likely to melt under excessive eddy current heat

80. Capacitive susceptance is a measure of__________?
0

A. a purely capacitive circuits ability to resist the flow of current

B. the extent of neutralisation of reactive power in a circuit

C. a purely capacitive circuits ability to pass current

D. reactive power in a circuit

81. The frequency of an alternating current is____________?
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A. the number of waves passing through a point in one second

B. the speed with which the alternator runs

C. the number of electrons passing through a point in one second

D. the number of cycles generated in one minute

82. Power factor of electric bulb is__________?
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A. leading

B. zero

C. unity

D. lagging

83. The phosphors for which of the following pair are 180 out of phase for VL, VC and VR______?
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A. Vc and VR

B. Vc and VL

C. none of the above

D. VL and VR

84. Which of the following waves has the highest value of peak factor ___________?
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A. Sine wave

B. Square wave

C. Triangular wave

D. Half wave rectified sine wave

85. In a purely inductive circuit__________?
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A. none of above is zero

B. actual power is zero

C. apparent power is zero

D. reactive power is zero

86. Time constant of a circuit is the time in seconds taken after the application of voltage to each___________?
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A. 63% of maximum value

B. 25% of maximum value

C. 90% of the maximum value

D. 50% of maximum value

87. Magnitude of current at resonance in R-L-C circuit________?
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A. depends upon the magnitude of L

B. depends upon the magnitude of R, Land C

C. depends upon the magnitude of C

D. depends upon the magnitude of R

88. Time constant of a capacitive circuit__________?
0

A. increases with the decrease of capacitance and decrease of resistance

B. increases with the increase of capacitance and decrease of resistance

C. increase with increase of capacitance and increase of resistance

D. increases with the decrease of capacitance and increase of resistance

89. Which of the following circuit component opposes the change in the circuit voltage ?
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A. Resistance

B. Inductance

C. Conductance

D. Capacitance

90. In a pure capacitive circuit if the supply frequency is reduced to 1/2, the current will__________?
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A. be reduced by half

B. be reduced to one fourth

C. be four times at high

D. be doubled

91. In a R-L-C circuit_________?
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A. all above are correct

B. exchange of power takes place between capacitor and supply line

C. exchange of power takes place between inductor and supply line

D. power is consumed in resistance and is equal to I R

E. exchange of power does not take place between resistance and the supply line

92. Ohm is unit of all of the following except___________?
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A. capacitance

B. resistance

C. capacitive reactance

D. inductive reactance

93. At _______ frequencies the parallel R-L circuit behaves as purely resistive
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A. low

B. high

C. very high

D. very low

94. A parallel AC. circuit in resonance will__________?
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A. have current in each section equal to the line current

B. have a high impedance

C. have a high voltage developed across each inductive and capacitive section

D. act like a resistor of low value

95. Skin effect occurs when a conductor carries current at_______ frequencies
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A. very low

B. medium

C. high

D. low

96. Which of the following coil will have large resonant frequency __________?
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A. A coil with large distributed capacitance

B. A coil with large resistance

C. A coil with low resistance

D. A coil with low distributed capacitance

97. The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA The power drawn by the circuit is__________?
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A. 12 kW

B. 22 kW

C. 64 kW

D. 32 kW

98. All definitions of power factor of a series R-L-C circuit are correct except__________?
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A. ratio of net reactance and impedance

B. ratio of W and VA

C. ratio of kW and kVA

D. ratio of J and Z

99. The ratio of active power to apparent power is known as factor__________?
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A. demand

B. power

C. load

D. form

100. The apparent power drawn by an A.C. circuit is 10 kVA and active power is 8 kW. The reactive power in the circuit is_________?
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A. 8 kVAR

B. 6 kVAR

C. 4 kVAR

D. 16 kVAR

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