Question Bank in AC Circuits

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Question Bank in AC Circuits

A. SINUSOIDAL VOLTAGE AND CURRENT 1. REE Board Exam September 2000

Find the average current during the half cycle given the instantaneous maximum value of 20 amperes.

A. 12.73 amperes C. 20 amperes

B. 14.14 amperes D. 10 amperes

2. REE Board Exam April 1997

The phase shift between the current and voltage vectors us due to the following except one

A. magnet coils C. power capacitors

B. electric flat iron D. fluorescent lamp 3. REE Board Exam April 2001

An alternating rectangular wave has a maximum value of 10 V and a frequency of 1 cycle per second. What is the average value of the wave?

A. 5 V C. 0

B. 10 V D. 7.07 V

4. REE Board Exam October 2000

A sinusoidal current wave has a maximum value of 20 A. What is the average value of one-half cycle?

A. 5 A C. 14.14 A

B. 12.7 A D. 0

What is the wavelength of a carrier wave with frequency of 100 megahertz?

A. 3.0 m C. 1.5 m

B. 7.5 m D. 6.0 m

A chart speed of a recording instrument is 25 mm/sec. One cycle of the signal being recorded extends over 5 mm. What is the frequency of the signal?

A. 20 cps C. 50 cps

B. 2 cps D. 5 cps

7. EE Board Exam April 1992

Determine the rms value of the current drawn by a 2 μF condenser, which is connected across a source of potential. The potential has a third and fifth harmonic components, which are 30% and 20% respectively of the fundamental. The fundamental sinusoidal component has a peak value of 1000 volts and 60 Hz frequency.

A. 0.89 A C. 0.91 A

B. 0.75 A D. 0.84 A

A 240-V, 25 Hz sinusoidal generator is connected to a 20 ohms resistor. Determine the instantaneous current when elapsed time is 0.01 second.

A. 15.43 A C. 16.97 A

B. 16.30 A D. 12.00 A

A wire carries a current i = 3 cos 314t amperes. What is the average current over 6 seconds?

A. 0 A C. 1.5 A

B. 3.0 A D. 0.532 A

Across a 230-V, 60 Hz power supply is a 15-ohm non-inductive resistor. What is the equation of the resulting current?

A. i = 21.68 sin 377t C. i = 15.33 sin 377t B. i = 26.56 sin 377t D. i = 28.16 sin 120t 11. EE Board Exam April 1991

Determine the effective value of the circuit current of an emf of 151 sin 377t is connected in series with a DC emf of 110 volts. Both supply a load of 10 + j8 ohms.

A. 10.3 A C. 13.8 A

B. 12.5 A D. 11.4 A

An alternating current and a direct current flow simultaneously in the same conductor. If the effective of the alternating current is 5 A and the direct current is 10 A, what will an AC ammeter read when connected in the circuit?

A. 7.5 A C. 11.18 A

B. 15 A D. none of these

If e = 100 sin (ωt – 30°) – 50 cos 3ωt + 25 sin (5ωt + 150°) and i = 20 sin (ωt + 40°) + 10 sin (3ωt + 30°) – 5 sin (5ωt – 50°). Calculate the power in watts.

A. 1177 C. 1043

B. 919 D. 1224

14. ECE Board Exam November 2001

It is the value of sine wave of voltage or current at one particular instant of time.

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B. effective value D. instantaneous value

If the combination of an ac voltage and a dc voltage has an instantaneous voltage that varies through a range from -2 V to +10 V, what is the peak ac voltage of the combination?

A. 10 V C. 6 V

B. 16 V D. 12 V

16. ECE Board Exam April 2001

Measured in Hertz, it is the number of cycles of alternating current per second.

A. frequency C. peak to peak

B. period D. wavelength

If an ac signal has an average voltage of 18 V, what is the rms voltage?

A. 16.2 V C. 25.38 V

B. 19.98 V D. 12.73 V

If an ac signal has a peak voltage of 55 V, what is the average value voltage?

A. 61.05 V C. 34.98 V

B. 38.86 V D. 86.35 V

What is the phase relationship between current and voltage in an inductor? A. in phase

B. current lags voltage by 90° C. voltage lags current by 90° D. current lags voltage by 180° 20. ECE Board Exam November 1995

If sine wave voltage varies from 0 to 200 V, how much is its instantaneous voltage at 90°?

A. 100 V

B. minimum voltage C. 200 V

D. half of its maximum voltage 21. ECE Board Exam November 2000

How many degrees are there in one complete wave cycle? A. 360 degrees C. 180 degrees

B. 90 degrees D. 720 degrees

When comparing rms voltage and average voltages, which of the following statement is true, assuming sine waves?

A. Either the rms voltage or the average voltage might be larger. B. The average voltage is always greater than the rms voltage.

C. There will always be a very large difference between the rms voltage and the average voltage.

D. The rms voltage is always greater than the average voltage.

It is the maximum instantaneous value of a varying current, voltage, or power equal to 1.414 times the effective value of a sine wave.

A. rms value C. effective value

B. peak to peak value D. peak value

It is the description of two sine waves that are in step with each other going through their maximum and minimum points at the same time and in same direction.

A. stepped sine waves B. sine waves in coordination C. phased sine waves D. sine waves in phase

What is the average voltage (Eave) output of a full wave rectifier with an

output of 100 volts peak?

A. 63.7 volts C. 141.4 volts

B. 14.14 volts D. 6.37 volts

The relation of the voltage across an inductor to it current is ____ A. Lagging the current by 90 degrees

B. Leading the current by 90 degrees C. In phase with the current

D. Leading the current by 180 degrees 27. ECE Board Exam April 1999

If two equal frequency ac signals of exactly 5 V each are combined with one of the signals 180 degrees out of phase with the other, what will be the value of the resultant voltage?

A. 2.25 V C. 0 V

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Kind of electric current where amplitude drops to zero periodically normally produced by rectifier circuits

A. alternating current B. varying direct current C. damped alternating current D. pulsating direct current

If an ac signal has an average voltage of 18 V, what is the rms voltage?

A. 16.2 V C. 25.38 V

B. 19.98 V D. 12.726 V

In electronic circuit the current that flows over a capacitor _____. A. In phase with the voltage

B. Leads the voltage by 180 degrees C. Lags the voltage by 90 degrees D. Leads the voltage by 90 degrees

31. Two current sources deliver current to a common load. The first source delivers a current whose equation is 25 sin 100πt amperes while the second delivers a current whose equation is 15 cos 100πt amperes. What is the rms value of the current in the load?

A. 29.15 A C. 20.6 A

B. 40 A D. 10 A

32. Two alternators A and B delivers 100 A and 150 A, respectively to a load. If these currents are out of phase by 30 electrical degrees, determine the total current drawn by the load.

A. 201.5 A C. 215.4 A

B. 250.0 A D. 241.8 A

33. When using circuit laws and rules we must use

A. maximum value C. effective value

B. average value D. peak to peak value

34. A 60 Hz frequency would cause an electric light to A. turn on and off 120 times per second

B. flicker noticeable

C. turn on and off 180 times per second D. turn on and off 60 times per second

35. The relationship between frequency f, number of revolutions per second n and pair of poles p is given by

A. f = n/p C. f = n/2p

B. f = np D. f = 2np

36. The difference between the peak positive value and the peak negative of an a.c. voltage is called the

A. maximum value C. average value

B. effective value D. peak to peak value

37. The greatest value attained during one half of the cycle is called the A. peak value C. r.m.s. value

B. average value D. effective value

38. The root mean square (r.m.s.) value of a.c. is the same as A. instantaneous value C. effective value

B. average value D. maximum value

39. The r.m.s. value of a sine wave is equal to

A. 0.637 maximum value C. 0.707 maximum value

B. 0.506 maximum value D. 1.414 maximum value 40. Form factor is defined as

A. r.m.s. value/peak value B. maximum value/r.m.s. value C. r.m.s. value/average value

D. effective value/ r.m.s. value

41. The value of form factor for a pure sine wave is

A. 1.414 C. 0.707

B. 0.637 D. 1.11

42. The value of peak factor for a pure sine wave is

A. 1.414 C. 0.707

B. 0.637 D. 1.11

43. If the current and voltage are out of phase by 90, the power is

A. 1.1 VI C. Maximum

B. minimum D. zero

44. If e1 = A sin t and e2 = B sin (t - ) then

A. e1 lags e2 by  C. e2 lags e1 by 

B. e2 leads e1 by  D. e1 leads e2 by 

45. Which of the following statements concerning the graph of figure below is most correct?

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0 1 2 3 time A. it represents ac B. it represents dc

C. it represents half-wave rectified ac D. it represents sum of ac and dc

46. Average value of a sine wave is √ times the maximum value

A. True B. False

47. The equation for 25 cycles current sine wave having rms value of 30 amperes will be

A. 30 sin 25t C. 30 sin 50t

B. 42.4 sin 25πt D. 42.4 sin 50πt

48. The voltage v = 90 cos (ωt – 161.5°) may be represented as a sine function by

A. 90 sin (ωt + 18.5°) C. 90 sin (ωt + 71.5°) B. 90 sin (ωt – 71.5°) D. 90 sin (ωt - 18.5°) 49. Which of the following frequencies has the longest period?

A. 1 Hz C. 1 kHz

B. 10 Hz D. 100 kHz

50. RMS value and the mean value is the same in case of A. square wave

B. sine wave C. triangular wave

D. half-wave rectified sine wave

51. If emf in a circuit is given by e = 100 sin 628t, the maximum value of voltage and frequency are

A. 100 V, 50 Hz C. 100 V, 100 Hz

B. 50√ V, 50 Hz D. 50√ V, 100 Hz

52. When the sole purpose of an alternating current is to produce heat, the selection of conductor is based on

A. average value of current C. rms value of current B. peak value of current D. any of the above 53. The form factor of dc supply voltage is always

A. infinite C. 0.5

B. zero D. unity

54. The frequency of a sinusoidal signal shown in figure is

A. 500 Hz C. 25 kHz

B. 1 kHz D. 500 kHz

55. The period of the voltage 2 cos 4500πt + 7 sin 7500πt is

A. 2.51 s C. 2.51 ms

B. 2.51 ns D. 2.51 μs

56. The a.c. system is preferred to d.c. system because ____ A. a.c. voltages can easily be changed in magnitude

B. d.c. motors do not have fine speed control C. high-voltage a.c. transmissions is less efficient D. d.c. voltage cannot be used for domestic appliances 57. In a.c. system, we generate sine wave form because ____

A. it can be easily drawn

B. it produces lest disturbance in electrical circuits C. it is nature’s standard

D. other waves cannot be produced easily 58. ____ will work only on d.c. supply.

A. Electric lamp C. Heater

B. Refrigerator D. Electroplating

59. ____ will produce a.c. voltage.

A. Friction C. Thermal energy

B. Photoelectric effect D. Crystal

60. In Fig. 1.1, the component of flux that will contribute to e.m.f. in the coil is ____

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Coil of N turns ω rad/sec

φmax Figure 1.1

A. max sin t C. max tan t

B. max cos t D. max cot t

61. In Fig. 1.1, the maximum e.m.f. induced in the coil is ____.

Coil of N turns ω rad/sec

φmax Figure 1.1

A. N max C. N max sin t

B. max D.  N max

62. A coil is rotating in the uniform field of an 8-pole generator. In one revolution of the coil, the number of cycles generated by the voltage is ____.

A. one C. four

B. two D. eight

63. An alternating voltage is given by v = 20 sin 157t. The frequency of the alternating voltage is ____.

A. 50 Hz C. 100 Hz

B. 25 Hz D. 75 Hz

64. An alternating current is given by i = 10 sin 314t. The time taken to generate two cycles of current is ____.

A. 0.02 second C. 0.04 second

B. 0.01 second D. 0.05 second

65. An alternating voltage is given by v = 30 sin 314t. The time taken by the voltage to reach –30 V for the first time is ____.

66. A sine wave has a maximum value of 20 V. Its value at 135 is ____.

A. 10 V C. 15 V

B. 14.14 V D. 5 V

67. A sinusoidal current has a magnitude of 3 A at 120. Its maximum value will be ____.

A. √ A C. √ A

B. √ A D. 6 A

68. An alternating current given by i = 10 sin 314t. Measuring time from t = 0, the time taken by the current to reach +10 A for the second time is ____.

69. An a.c. generator having 10 poles and running at 600 r.p.m. will generate an alternating voltage of frequency _____

A. 25 Hz C. 50 Hz

B. 100 Hz D. 200 Hz

70. We have assigned a frequency of 50 Hz to power system because it ____ A. can easily be obtained

B. gives best result when used for operating both lights and machinery

C. leads to easy calculation D. none of the above

71. An alternating voltage is given by v = 100 sin 314t volts. Its average value will be ____.

A. 70.7 V C. 63.7 V

B. 50 V D. 100 V

72. An alternating current whose average value is 1 A will produce ____ 1 A d.c. under similar conditions.

A. less heat than C. the same heat as

B. more heat than D. none of the above

73. A sinusoidal alternating current has a maximum value of Im. Its average

value will be ____.

A. Im/ C. 2Im/

B. Im/2 D. none of the above

74. The area of a sinusoidal wave over a half-cycle is ____

A. max. value / 2 C. max. value / 

B. 2 x max. value D. max. value / 2

75. An alternating voltage is given by v = 200 sin 314t. Its r.m.s. value will be ____

A. 100 V C. 141.4 V

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76. The r.m.s. value of sinusoidally varying current is ____ that of its average value.

A. more than C. same as

B. less than D. none of the above

77. Alternating voltages and currents are expresses in r.m.s. values because ____

A. they can be easily determined B. calculations become very simple C. they give comparison with d.c.

D. none of the above

78. The average value of sin2__{over a complete cycle is ____}

A. +1 C. ½

B. -1 D. zero

79. The average value of sin over a complete cycle is ____.

A. zero C. -1

B. +1 D. ½

80. An alternating current is given by i = Im sin . The average value of squared

wave of this current over a complete cycle is ____

A. Im/2 C. 2Im/

B. Im/ D. 2Im

81. The form factor a sinusoidal wave is ____

A. 1.414 C. 2

B. 1.11 D. 1.5

82. The filament of a vacuum tube requires 0.4 A d.c. to heat it. The r.m.s. value of a.c. required is ____.

A. 0.4 x √ C. 0.8 / √

B. 0.4 / 2 A D. 0.4 A

83. A 100 V peak a.c. is as effective as ____ d.c.

A. 100 V C. 70.7 V

B. 50 V D. none of the above

84. The form factor of a ____ wave is 1.

A. sinusoidal C. triangular

B. square D. saw tooth

85. Out of the following ____ wave is the peakiest.

A. sinusoidal C. rectangular

B. square D. triangular

86. The peak factor of a sine wave form is ____.

A. 1.11 C. 2

B. 1.414 D. 1.5

87. When a 15-V square wave is connected across a 50-V a.c. voltmeter, it will read ____.

A. 15 V C. 15 /√

B. 15 x √ D. none of the above

88. The breakdown voltage of an insulation depends upon ____ value of alternating voltage.

A. average C. peak

B. r.m.s. D. twice the r.m.s.

89. The peak factor of a half-wave rectified a.c. is ____.

A. 1.57 C. 1.11

B. 2 D. 1.4142

90. The form factor of a half-wave rectified a.c. is ____

A. 2 C. 1.414

B. 1.11 D. 1.57

91. When 200 V sinusoidal peak-to-peak is connected across an a.c. voltmeter, it will read ____

A. 141.4 V C. 70.7 V

92. In Fig. 1.2, the wave that will produce maximum heat under the similar conditions is ____.

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10 A -10 A 0 t i t t 10 A 10 A 10 A -10 A -10 A 0 0 0 i i i Figure 1.2

A. square wave C. triangular wave

B. sinusoidal wave D. saw tooth wave

93. In Fig. 1.2, ____ wave will have the highest average value.

10 A -10 A 0 t i t t 10 A 10 A 10 A -10 A -10 A 0 0 0 i i i Figure 1.2

A. saw tooth C. triangular

B. square D. sinusoidal

94. The average value of a sinusoidal current is 100 A. Its r.m.s value is ____.

A. 63.7 A C. 141.4 A

B. 70.7 A D. 111 A

95. A current wave is given by i = 4 + 2√ sin 3 + 4√ sin 5. The r.m.s. value of current wave is ____.

A. 10 A C. √ A

B. 6 A D. 5 A

96. In Fig. 1.3, current is given by i = Im sin . The voltage equation will be ____.

Figure 1.3 θ v i φ A. Vm sin  C. Vm sin ( - ) B. Vm sin ( + ) D. Vm sin ( - 2)

97. The waveforms of voltage and current shown in Fig. 1.3 would exist in ____ circuit. Figure 1.3 θ v i φ A. a resistive C. an inductive

B. a capacitive D. none of the above

98. An alternating voltage or current is a ____.

A. scalar quantity C. phasor

B. vector quantity D. none of the above

99. Three parallel circuits take the following currents: i1 = 5 sin 314t, i2 = 30 sin

(314t + /2) and i3 = 25 sin (314t - /2). The expression for the resultant

current is ____.

A. 25 sin (314t + /3) C. 10 sin (314t - /6) B. 5 sin (314t + /2) D. 5√ sin (314t + /4)

100. The sum of the following two e.m.f’s will be ____ e1 = 10 sin t e2 = 10 cos t

A. 10 C. 14.14 cos t

B. 20 sin t D. 14.14 sin (t + /4)

101. Each of the three coils generates an e.m.f. of 230 V. The e.m.f. of second leads that of the first 120 and the third lags behind the first by the same angle. The resultant e.m.f. across the series combination of the coils is ____.

A. 0 V C. 690 V

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102. In Fig. 1.4, I1 + I2 is equal to ____ Figure 1.4 60° I1 I2 _I 3 6 A 3 A _{4 A} A. 3 A C. 9 A B. 4.33 A D. 3.43 A 103. In Fig. 1.4, I2 + I3 is equal to ____ Figure 1.4 60° I1 I2 _I 3 6 A 3 A _{4 A} A. 7 A C. 5 A

B. √ A D. none of the above

104. In Fig. 1.5, E1 + E2 + E3 + E4 is equal to E3 = 20 V E1 = 9 V E4 = 6 V Figure 1.5 E2 = 24 V A. 7 V C. 20 V

105. In Fig. 1.5, ____ will have the least value.

E3 = 20 V E1 = 9 V E4 = 6 V Figure 1.5 E2 = 24 V A. E1 + E2 + E3 + E4 C. E1 + E2 - E3 – E4 B. E1 + E2 + E3 – E4 D. -E1 + E4

106. In a pure resistive a.c. circuit, the frequency of power curve is ____ that of the circuit frequency.

A. half C. thrice

B. twice D. same as

107. In a pure resistive circuit, the instantaneous voltage and current are given by: v = 250 sin 314t volts

i = 10 sin 314t amperes The peak power in the circuit is

A. 1250 W C. 2500 W

B. 25 W D. 250 W

108. In a pure resistive circuit, the instantaneous voltage and current are given by: v = 250 sin 314t volts

i = 10 sin 314t amperes The average power in the circuit is

A. 2500 W C. 25 W

B. 250 W D. 1250 W

109. An alternating voltage is applied to a pure inductive circuit. The current equation will be

A. C. ( ⁄ )

B. ( ⁄ ) D. ( ⁄ ) 110. The inductive reactance of a circuit is ____ frequency.

A. directly proportional to C. independent of B. inversely proportional D. none of the above 111. Power absorbed in a pure inductive circuit is zero because

A. reactive component of current is zero B. active component of current is maximum C. power factor of the circuit is zero

D. reactive and active component of current cancel out

112. An alternating voltage is applied to a pure capacitive circuit. The current equation will be

A. C. ( ⁄ )

B. ( ⁄ ) D. ( ⁄ )

113. The capacitive reactance of a circuit is ____ frequency. A. independent of

B. inversely proportional to

C. directly proportional to D. none of the above

114. An a.c. current given by i = 14.14 sin (t + /6) has an rms value of ____ amperes and a phase of ____ degrees.

A. 10, 30 C. 1.96 , -30

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115. If e1 = A sin t and e2 = B sin (t – ), then

A. e1 legs e2, by  C. e2 leads e1, by 

B. e2 lags e1 by  D. e1 is in phase with e2

116. From the two voltage equations eA = Em sin 100t and eB = Em sin (100t +

/6), it is obvious that A. eA leads eB 30

B. eB achieves its maximum value 1/600 second before eA does C. eB lags behind eA

D. eA achieves its zero value 1/ 600 before eB

117. The r.m.s. value a half-wave rectified current is 10 A, its value for full wave rectification would be ____ amperes.

A. 20 C. 20/π

B. 14.14 D. 40/

118. A resultant current is made of two components: a 10 A d.c. components and a sinusoidal component of maximum value 14.14 A. The average value of the resultant current is ____ amperes and r.m.s. value is ____ amperes.

A. 0, 10 C. 10, 14.14

B. 24, 24.14 D. 4.14, 100

119. The r.m.s. value of sinusoidal ac current is equal to its value at an angle of ____ degree.

A. 60 C. 30

B. 45 D. 90

120. Two sinusoidal currents are given by the equations: i1 = 10 sin (t + /3) and

i2 = 15 sin (t - /4). The phase difference between them is ____ degrees.

A. 105 C. 15

B. 75 D. 60

121. A sine wave has a frequency of 50 Hz. Its angular frequency is ____ radian/second.

A. 50/ C. 50π

B. 50/2 D. 100

122. An a.c. current is given by i = 100 sin 100. It will achieve a value of 50 A after ____ second.

A. 1/600 C. 1/1800

B. 1/300 D. 1/900

123. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 10 . If frequency is increased to 100 Hz reactance becomes ____ ohm.

A. 20 C. 2.5

B. 5 D. 40

124. A complex current wave is given by i = 5 + 5 sin 100t ampere. Its average value is ____ ampere.

A. 10 C. √

B. 0 D. 5

125. The current through a resistor has a wave form as shown in Fig. 1.6. The reading shown by a moving coil ammeter will be ____ ampere.

ωt 5 A i(t) 0 π 2π 3π Fig. 1.6 A. √ C. 5/π B. √ D. 0

126. A constant current of 2.8 exists in a resistor. The rms value of current is

A. 2.8 A C. 1.4 A

B. about 2 A D. undefined

127. The rms value of a half-wave rectified symmetrical square wave current of 2 A is

A. √ A C. √ A

B. 1 A D. √ A

128. The rms value of the voltage v(t) = 3 + 4 cos (3t) is

A. √ V C. 7 V

B. 5 V D. (3 + 2√ ) V

129. The rms value of the resultant current in a wire which carries a dc current of 10 A and a sinusoidal alternating current of peak value 20 A is

A. 14.1 A C. 22.4 A

B. 17.3 A D. 30.0 A

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T/2 v T 3T/2 2T 5T/2 t A. √ V C. 1/3 V B. √ V D. √ V

131. The rms value of the periodic waveform given in the figure is

T/2 T 6 A

-6 A

A. √ A C. √ A

B. √ A D. 1.5 A

132. If i1 = 120 cos (100πt + 30°) and i1 = -0.1 cos (100πt + 100°) then i2 leads i1 by

____.

A. -110 degrees C. -60 degrees

B. 60 degrees D. 110 degrees

133. If v1 = sin (ωt + 30°) and v2 = -5 sin (ωt - 15°) then v1 leads v2 by ____.

A. 225 degrees C. 45 degrees

B. 30 degrees D. none of the above

134. The rms value of a rectangular wave of period T, having a value of +V for a duration, T1 (<T) and –V for the duration T - T1 = T2 equals ____.

A. V C. V/√

B. (T1 - T2)/T*V D. (T1/T2)* V

135. The rms value of the voltage waveform v(t) = sin 10t + sin 20t is ____.

A. 1 C. 1/√

B. 1/2 D. √

136. For the voltage waveform v(t) = 2 + cos (ωt + 180°) find the ratio of Vrms/Vave.

A. √ C. π/2

B. √ D. π

137. The rms value of the periodic wave form e(t) shown in the figure is ____.

A. √ C. √

B. √ D. √

138. Which of the waveforms are having unity peak factor?

A -A t i t A -A 0 0 i T T/2 π 2π A t 0

Fig. a Fig. b Fig. c

A. figure a and b C. figure a and c

B. figure b and c D. none of the above

139. The length of time between a point in one cycle to the same point of the next cycle of an AC wave is the ____.

A. frequency C. magnitude

B. period D. polarity

140. In an experiment, a sinusoidal wave form is observed to complete 8 cycles in 25 msec. Determine the frequency of the wave form.

A. 320 Hz C. 200 Hz

B. 40 Hz D. 64 Hz

141. If emf in a circuit is given by e = 100 sin 628t, the maximum value of voltage and frequency is ____.

A. 100 V, 50 Hz C. √ V, 50 Hz

B. 100 V, 100 Hz D. √ V, 100 Hz

142. A sinusoidal voltage wave has an RMS value of 70.71 V and a frequency of 60 Hz. Determine the value of the voltage 0.0014 second after the wave crosses the ωt axis.

A. 70.71 V C. 50 V

B. 100 V D. 141.42 V

143. An alternating current varying sinusoidally with frequency of 50 Hz has an RMS value of 20 A. At what time measured from the positive maximum value will the instantaneous current be 14.14 A?

(11)

B. 1/200 sec D. 1/400 sec

144. The average value of the function i = 50 sin ωt + 30 sin 3ωt is equal to ____.

A. 31.8 A C. 38.2 A

B. 25 A D. 51.43 A

145. For 200 Vrms value triangular wave, the peak value is equal to ____.

A. 200 V C. 282 V

B. 222 V D. 346 V

146. Determine the rms value of a semi-circular current wave which has a maximum value of A.

A. 0.816A C. 0.866A

B. 0.23 A D. 0.707A

147. The rms value of a half-wave rectified current is 100 A. Its value for full-wave rectification would be ____ amperes.

A. 141.4 A C. 200/π A

B. 200 A D. 400/π A

148. A half-wave rectified sine wave has an average value of 100 amp. What is the effective value?

A. 157 A C. 70.71 A

B. 444 A D. 100

149. The form factor of a half-wave rectified alternating current is ____.

A. 1.11 C. 1.73

B. 1.57 D. 1.0

150. Three alternating currents are given by i1 = 141 sin (ωt + 45°) A; i2 = 30 sin

(ωt + 90°) A; i3 = 20 cos (ωt – 120°) A. Find the equation of the resultant

current.

A. 167.4 sin (ωt + 45.66°) C. 143.8 sin (ωt + 51.4°)

B. 74.6 sin ωt D. 64.7 sin (ωt – 30°)

151. The maximum value of a sine wave AC voltage which will produce heat in a resistor at the same average rate as 115 V of direct current is ____.

A. 81.3 V C. 162.6 V

B. 115 V D. 230 V

152. A sinusoidal voltage source has a peak value of 150 volts. What equivalent DC voltage source would produce the same heating effect in a 1-ohm resistor?

A. 15 V C. 95 V

B. 212 V D. 106 V

153. The effective value of v(t) = 100 + A sin ωt is known to be 103.1. The amplitude A of the sine term is ____.

A. 25 C. 35.48

B. 4.85 D. 100

154. An alternating current and a direct current flow simultaneously in the same conductor. If the effective of the AC is 8 A and DC is 12 A, what will an AC ammeter read when connected in the circuit?

A. 14.42 A C. 11.66 A

B. 12 A D. 16.49 A

155. Find the reading of an AC voltmeter connected across the series source of 100 sin (ωt – π/2) and 100 sin ωt.

A. 100 C. 170.71

B. 130.65 D. 184.78

156. A voltage is given be v = 100 sin 314t. How long does it take this wave to complete one fourth of a cycle?

A. 20 ms C. 5 ms

B. 10 ms D. 1 ms

157. When a 15 V square wave is connected across a 50 volt AC voltmeter, it will read ____.

A. 21.21 V C. 15 V

B. 10.61 V D. 9.55 V

158. Calculate the effective value of v(t) = 100 sin 400t + 50 sin 800t + 10 cos 1200t V.

A. 79.5 V C. 112.25 V

B. 57.9 V D. 121. 52 V

159. The magnetic field energy of an inductor changes from maximum value to minimum value in 5 ms when connected to an ac source. The frequency of the source is

A. 20 Hz C. 200 Hz

B. 50 Hz D. 500 Hz

160. Non-sinusoidal waveforms are made up of A. different sinusoidal waveforms

B. fundamental and even harmonics C. fundamental and odd harmonics D. even and odd harmonics only

(12)

A. it contains even harmonics

B. phase difference between even harmonics and fundamental is 0 or π C. it contains odd harmonics

D. phase difference between even harmonies and fundamental is either π/2 or 3π/2

162. The r.m.s. value of the complex voltage given by √ √ is

A. √ C. √

B. 20 D. 192

163. In a 3-phase system, ____th harmonic has negative phase sequence of RBY.

A. 9 C. 5

B. 13 D. 15

164. A complex current wave is given by the equation . The r.m.s. value of the current is ____ ampere.

A. 16 C. 10

B. 12 D. 8

165. When pure inductive coil is fed by a complex voltage wave, its current wave A. has larger harmonic content

B. is more distorted

C. is identical with voltage wave D. shows less distortion

166. A complex voltage wave is applied across a pure capacitor. As compared to the fundamental voltage, the reactance offered by the capacitor to the third harmonic voltage would be

A. nine times C. one-third

B. three times D. one-ninth

167. Which of the following harmonic voltage components in a 3-phase system would be in phase with each other?

A. 3rd_{, 9}th_{, 15}th_etc. B. 7th_{, 13}th_{, 19}th_etc.

C. 5th_{, 11}th_{, 17}th_etc.

D. 2nd_{, 4}th_{, 6}th_etc.

168. An alternating voltage is one that A. varies continuously in magnitude B. reverses periodically in polarity C. never varies in magnitude D. both A and B

169. One complete revolution of a conductor loop through a magnetic field is called a(n)

A. octave C. cycle

B. decade D. alternation

170. For a sine wave, one half cycle is often called a(n)

A. alternation C. octave

B. harmonic D. period

171. For a sine wave, the number of complete cycles per second is called the

A. period C. frequency

B. wavelength D. phase angle

172. To compare the phase angle between two waveforms, both must have A. the same amplitude C. different frequency

B. the same frequency D. both A and B

173. The value of alternating current or voltage that has the same heating effect as a corresponding dc value is known as the

A. peak value C. rms value

B. average value D. peak-to-peak value

174. For an ac waveform, the period refers to A. the number of complete cycles per second B. the length of time required to complete one cycle

C. the time it takes for the waveform to reach its peak value D. none of the above

175. The wavelength of a radio wave is A. inversely proportional to its frequency

B. directly proportional to its frequency C. inversely proportional to its amplitude D. unrelated to its frequency

176. Unless indicated otherwise, all sine wave ac measurements are in A. peak-to-peak values C. rms values

B. peak values D. average values

177. A unit step voltage is applied across an inductor. The current through the inductor will be

A. zero for all time B. a step function C. a ramp function

(13)

178. A ramp current flowing through an initially relaxed capacitor will result in a voltage across it that

A. varies inversely with time B. remains constant

C. varies directly with time D. varies as the square of time

179. The voltage v(t) = t u(t) volts is connected across a 1 H inductor having an initial current of -1 A. The net current will be zero at time t equal to

A. 0 C. √ seconds

B. √ seconds D. 1 seconds

180. A voltage waveform v (t) = 12t2_{is applied across 1H Inductor for t ≥ 0, with}

initial current through it being zero. The current through the inductor for t ≥ 0 is given by

A. 12t C. 12t3

B. 24t D. 4 t3

181. It is desired to have a constant direct current i(t) through the ideal inductor L. The nature of the voltage source v(t) must

A. constant voltage

B. linearly increasing voltage C. an ideal impulse

D. exponentially increasing voltage

182. For the current and voltage waveforms, identify the element & its value.

A. L, 25 H C. L, 2 H

B. C, 25 F D. C, 2 F

183. The voltage and current waveforms for an element are shown in the figure. Find the circuit element and its value.

A. L and 25 H C. L and 1 H

B. C and 25 F D. C and 1 F

184. What is the rms value of a square wave with an amplitude of 10 A and frequency of 1 Hz?

A. 0 A C. 5 A

B. 10 A D. 7.07 A

185. What is the frequency in kHz of a radio signal whose wavelength is 15 m?

A. 10,000 C. 15,000

B. 20,000 D. 20,500

B. SERIES CIRCUITS

186. REE Board Exam September 2003

The following are in series R = 1,000 Ω, L = .100 μH and C = 20,000 pF. The voltage across the circuit is 100 V, 60 kHz. What is the total impedance expressed in ohms?

A. 1882 ohms C. 2132 ohms

B. 1000 ohms D. 1885 ohms

A series circuit has an applied voltage of v = 220 sin (ωt + 30°) and draws a current of i = 10 sin (ωt - 30°). What is the average power and power factor of the circuit?

A. 1,905 W, 86.6% lagging C. 2,200 W, 100% B. 1,905 W, 86.6% lagging D. 1,100 W, 50% lagging

A coil has an impedance of 75.4 Ω when connected a across a source of 60 Hz. The same coil yields an impedance of 54.8 Ω when connected across a source having a different frequency of 30 Hz. What is the coil’s inductance?

A. 245.7 mH C. 158.6 mH

B. 512.8 mH D. 341.7 mH

A circuit consists of a 4 ohms resistor and a 300 μF capacitor in series. It is connected across a 60 Hz voltage source with a 500 V peak voltage. What is the phasor form of the current?

A. A C. _A

B. A D. A

Find the power in a circuit if i(t) = 10 sin (ωt - 30) and v(t) = 220 sin (ωt + 30).

A. 550 watts C. 1900 watts

(14)

A current of 2.5 A flows through a series circuit consisting of a 100 Ω resistor and an unknown capacitor across a source of 460 V, 50 Hz. What is the value of the capacitive reactance?

A. XC = 91.86 Ω C. XC = 154.45 Ω

B. XC = 39.19 Ω D. XC = 184.0 Ω

In a series RC circuit the voltage across the capacitor and the resistor are 60 volts and 80 volts respectively. The total voltage is

A. 70 C. 140

B. none of these D. 100

193. EE Board Exam October 1984

An industrial coil has a resistance of 32 ohms and reactance of 24 ohms and rated 440 volts at 60 Hz. A factory will connect the coil to a 440 V, 50 Hz supply. Solve for the value of a series resistor needed to avoid over-current condition.

A. 2.07 ohms C. 2.44 ohms

B. 2.64 ohms D. 2.25 ohms

Two relays each with 20 ohms resistance and 0.16 H inductance are connected in series. What is the equivalent impedance?

A. 20 + j102.2 Ω C. 40 + j120.63 Ω

B. 20 + j95.32 Ω D. 40 + j25.32 Ω

An inductive coil takes a current of 2 A and consumes 160 W when connected to a 240 V ac supply. A second coil when connected across the same supply takes 3 A and 500 W. Find the total power when the two coils are connected in series to this supply,

A. 144.56 W C. 150.22 W

B. 134.31 W D. 128.35 W

A coil draws 1875 watts when connected to a 150 V dc source. It consumes 30.72 watts when use on a 240 V, 60 Hz ac source. Find the inductance of the coil.

A. 0.0255 H C. 0.0153 H

B. 0.0341 H D. 0.0240 H

A current of 10 A and a power factor of 0.8 lagging is taken form a single phase 250 volt supply. The reactive power of the system is

A. 1500 vars C. 2500 vars

B. 2000 vars D. none of these

The resistor of 6 Ω and unknown impedance coil in series draws 12 A from a 120 V, 60 Hz line. If the real power taken from the line is 1152 watts, what is the coil inductance?

A. 15.9 mH C. 20 mH

B. 10 mH D. 1.59 mH

Determine the power factor angle in the series circuit which consists of R = 25 Ω, L = 0.2 H, across a power supply of 200 V, 30 Hz.

A. 36.4° C. 52.4°

B. 46.4° D. 56.4°

The impedance coils absorbs 250 watts when connected across 220 V, 60 Hz mains. It is then connected across 110 V, 25 Hz mains and also absorbs 250 watts. What is the inductance of the coil?

A. 0.125 H C. 0.154 H

B. 0.149 H D. 0.163 H

In laboratory experiment, the impedance of the coil was obtained at 60 Hz and 30 Hz. These are 75.48 ohms and 57.44 ohms respectively. What is the inductance of the coil?

A. 150 mH C. 42.5 mH

B. 182.5 mH D. 2.1 mH

A 10 ohms inductive resistor is connected in series with an unknown capacitance. At 60 Hz the impedance of the circuit is 10 + j11.72 ohms. At 30 Hz the impedance of the circuit is 10 – j5 ohms. What is the value of L in millihenrys?

A. 50 C. 100

B. 500 D. 250

An impedance coil takes 10 A and absorbs 250 W when connected across a 220 V, 60 Hz source. What power will it absorb when connected across 110 V, 25 Hz mains?

(15)

B. 239 W D. 339 W

An industrial coil has a resistance of 32 ohms and a reactance of 24 ohms and rated 440 volts at 60 Hz. A factory will connect the coil to a 440 V, 50 Hz supply. How much percentage over-current will the coil suffer?

A. 5% C. 6%

B. 10% D. 8%

205. REE Board Exam March 1998

A 25 Ω resistor connected in series with a coil of 50 Ω resistance and 150 mH inductance. What is the power factor of the circuit?

A. 85% C. 90%

B. 80% D. 75%

A current of 2.5 A flows through a series circuit consisting of a 100 ohm resistor and an unknown capacitor across a source of 460 V, 50 Hz. What is the value of the capacitive reactance?

A. XC = 91.86 Ω C. XC = 154.45 Ω

B. XC = 39.19 Ω D. XC = 184 Ω

The ohmic resistance of a large magnetic contactor is measured to be 20 ohms. A 230 V is impressed on the contractor and the current is taken as 3.2 A. Neglecting core loss, determine the inductance of the contractor in mH?

A. 261 C. 183

B. 315 D. 251

A load of 20 + j35 Ω is connected across a 220 V source. Determine the power factor and the VARS.

A. 49.6%, 1042 vars C. 85.3%, 975 vars

B. 52.2%, 1023 vars D. 42.3%, 1087 vars

Find the total impedance in rectangular form for the following three series impedances:

ohm, ohm, 34 ohm. A. 66.52 + j23.46 Ω C. 74.31 + j21.56 Ω

B. 68.34 + j20.54 Ω D. 67.70 + j22.04 Ω

An impedance draws a current i = 10 cos (ωt – 30°) A from a voltage, v = 220 sin (ωt + 30°) V. What is the impedance?

A. 15.6 – j15.6 Ω C. 19.1 – j11.1 Ω

B. 15.6 + j15.6 Ω D. 11.0 + j19.1 Ω

A series resistance-capacitance (R-C) circuit is connected to a 230 volt 60 cycle source. If the power taken by the circuit is 4,800 watts and the voltage drop across the resistor is 115 volts, calculate the capacitance of the capacitor.

A. 540 μF C. 556 μF

B. 530 μF D. 503 μF

A 50 μF and 100 μF capacitors are connected in series and across a 100 sin (ωt + 30°) voltage. Write the equation of the current.

A. 1.26 sin (ωt + 120°) A C. 5.65 sin (ωt + 120°) A B. 1.26 sin (ωt + 90°) A D. 5.56 sin (ωt + 90°) A 213. EE Board Exam April 1993

A V, 120 Hz generator and a V, 60 Hz generator are connected in series with a 60 V battery and a coil. The resistance and inductance of the coil are 3  and 2.65 mH, respectively. Determine the rms current of the coil.

A. 42.54 A C. 43.55 A

B. 44.24 A D. 40.44 A

A series circuit composed of 100-ohm resistor and a 20-microfarad capacitor connected across a 240-V, 60 Hz line. Which of the following answers is WRONG?

A. the impedance of the circuit is 167 ohms

B. angle between the current and the voltage vectors is 53.1 degrees C. the resulting current is 0.723 ampere

D. the voltage across the resistance is 144.6 volts 215. REE Board Exam April 1994

A capacitance is connected to a 115-V, 25 Hz mains and takes 5 A. What current will it take when the capacitance and the frequency are both doubled?

A. 2.5 A C. 20 A

B. 5 A D. 10 A

A capacitor is rated 100 kVAR, 380 V, 50 Hz, What will its rating be at 60 Hz, 220 V?

(16)

B. 40 kVAR D. 57.7 kVAR 217. REE Board Exam October 1992

A resistor and a capacitor are connected in series across a supply of 250 V. When the supply frequency is 50 Hz the current in the circuit is 5 A. When the supply frequency is 60 Hz, the current is 5.8 A. Find the value of the capacitance.

A. 58.3 μF C. 60.2 μF

B. 69.1 μF D. 70.2 μF

A series circuit composed of a 0.2 Henry inductor and a 74-microfarad capacitor is connected to a 60 V variable frequency source. At what frequency is the current be 4 amperes with a lagging power factor?

A. 50 Hz C. 48 Hz

B. 51 Hz D. 49 Hz

The maximum instantaneous voltage and current output of an alternator are 300 V and 20 A, respectively. What is the power output in watts if the voltage leads the current by 30°?

A. 2598 C. 5196

B. 3000 D. 6000

A 50-microfarad is connected in series with a coil having 50 ohms resistance and 150 mH inductance. The source voltage is 100 sin (ωt – 120°) V. What is the maximum power?

A. 199 watts C. 212 watts

B. 147 watts D. 165 watts

An impedance draws a current i = 10 cos (ωt – 30°) A from a voltage v = 220 sin ωt. What is the maximum power?

A. 2200 watts C. 190.5 watts

B. 1100 watts D. 1320 watts

An incandescent lamp load generally considered to be made up of resistors take 4.8 kW from a 120 V ac source. The instantaneous maximum value of power is

A. 4800 W C. 480 W

B. 2400 W D. 9600 W

The term used for an out-of-phase, non-productive power associated with inductors and capacitors?

A. peak envelope power C. true power

B. effective power D. reactive power

What is the capacitive reactance of a 33 microfarad capacitor at 6500 Hz?

A. 7.4 0hms C. 0.74 ohms

B. 96 0hms D. 1122 ohms

The power dissipated across the resistance in an AC circuit.

A. true power C. reactive power

B. real power D. apparent power 226. ECE Board Exam April 2000

What is the capacitive reactance of a 33 microfarad capacitor at 500 Hz?

A. 1,000,000 ohms C. 0 ohms

B. 144 ohms D. 9.55 ohms

What is the reactance of a 25 mH coil at 600 Hz?

A. 0.011 ohm C. 785 ohms

B. 94,000 ohms D. 94 ohms

Ignoring capacitance effects, what is the impedance of a 250 mH coil with an internal resistance of 55 ohms at 60 Hz?

A. 149.2 ohms C. 94.2 ohms

B. 109 ohms D. 10,900 ohms

Ignoring any inductive effects, what is the impedance of RC series capacitor made up of a 56 kilo ohms resistor and a 0.033 μF capacitor at a signal frequency of 450 Hz?

A. 66,730  C. 10,730 

B. 57,019  D. 45,270 

Assuming an ideal capacitor, with no leakage, what is the capacitive reactance of 10 microfarad capacitance of DC (0 Hz)?

A. 0 ohms B. 16000 ohms C. 1,000,000 ohms

(17)

The impedance in the study of electronics is represented by resistance and _____

A. Reactance

B. Capacitance C. Inductance

D. Inductance and capacitance 232. ECE Board Exam November 2000

One of the following satisfies the condition of Ohm’s Law

A. Application to metals which heated up due to flow of current over them B. Application to AC circuit having its impedance used in place of resistance C. Application to semiconductor

D. Application to vacuum radio valves

233. The effective voltage across a circuit element is (20 + j10) and the effective current through the element is 4 – j3 A. Calculate the true and reactive power taken by the element.

A. 50 watts & 100 vars lagging

B. 50 watts & 100 vars leading C. 110 watts & 20 vars lagging D. 110 watts & 20 vars leading

234. The voltage across a given circuit is 75 + j50 V. What is the power supplied to the circuit if the current through it is (8 – j5) A?

A. 850 W C. 750 W

B. 550 W D. 350 W

235. Find average power in a resistance R = 10 ohms if the current in series form is i = 10 sin ωt + 5 sin 3ωt + 2 sin 5ωt amperes.

A. 65.4 watts C. 546 watts

B. 645 watts D. 5.46 watts

236. Across a 230-V, 60 Hz power supply is a 15-ohm non-inductive resistor. What is the equation of the voltage and resulting current?

A. e = 398.4 sin 60t and i = 21.6 sin 60t B. e = 325.5 sin 377t and i = 21.6 sin 377t

C. e = 230 sin 377t and i = 15.3 sin 377t D. e = 230 sin 120t and i = 15.3 sin 120t

237. A resistor R and a capacitor C are connected in series across a 100 V, 60 cycle source. The reading of an ammeter connected in the circuit is 2 A and

the reading of a voltmeter connected across the capacitor is 80 V. Calculate the values of R and C.

A. 66 Ω & 30 μF C. 30 Ω & 66 μF B. 30 Ω & 60 μF D. 36 Ω & 60 μF

238. A series circuit consisting of a 66.2 μF capacitor and a variable resistor. For what two values of resistance will the power taken by the circuit be 172.8 watts, if the impressed 60-cycle emf is 120 volts?

A. 85.33 & 3.33 ohms C. 5.33 & 3.0 ohms B. 53.33 & 30 ohms D. 83.33 & 5.33 ohms

239. A series circuit composed of 0.2 H inductor and a 74 μF capacitor is connected to a 60 V variable frequency source. At what frequency will the current be 4 A with lagging power factor?

A. 47.767 Hz C. 60 Hz

B. 74.68 Hz D. 50 Hz

240. A 30 ohm resistor is connected in parallel with an inductor of inductive reactance XL. The combination is then connected in series with a capacitor

of reactance XC. What is the value of XL and XC if the total impedance is 1.92

ohms?

A. 7.84 and 7.34 C. 44.8 and 84.21

B. 47.4 and 47.3 D. 84.7 and 34.7

241. An impedance of 100 Ω resistance and an unknown inductance is connected across the capacitor. The resulting impedance is a pure resistance of 500 Ω if ω = 105_{rad/sec. Calculate the values of inductor and capacitor.}

A. 1 μF & 2 mH C. 7 μF & 3 mH B. 5 μF & 1 mH D. 0.04 μF & 2 mH

242. The voltage across the resistor, inductor and capacitor in series is 60 V, 90 V and 10 V respectively. What is the voltage across this circuit?

A. 160 V C. 100 V

B. 140 V D. 50 V

243. The open circuit voltage of an alternator is 127 V and its internal impedance is Ω. Find the voltage across a load of Ω.

A. V C. V

B. V D. V

244. The maximum values of alternating voltage and current are 400 V and 20 A, respectively. In a circuit connected to 50 Hz supply and these quantities are sinusoidal. The instantaneous values of voltage and current are 283 V and 10 A respectively at t = 0 both increasing positively. What is power factor of the circuit?

(18)

A. 0.707 C. 0.85

B. 0.83 D. 0.965

245. The potential difference measured across a coil is 4.5 V, when it carries a direct current of 9 A. The same coil when carries an alternating current of 9 A at 25 Hz, the potential difference is 24 V. Find the power when it is supplied by 50 V, 50 Hz supply.

A. 45 W C. 63 W

B. 54 W D. 30 W

246. Two coils A and B are connected in series across a 240 V, 50 Hz supply. The resistance of A is 5 Ω and the inductance of B is 0.015 H. If the input from the supply is 3 kW and 2 kVAR, find the inductance of A and resistance of B.

A. 0.0132 H & 8.3 Ω C. 0.026 H & 12 Ω B. 0.215 H & 3.8 Ω D. 0.031 H & 5.3 Ω

247. A current of 5 A flows through a non-inductive resistance in series with a choking coil when supplied at 250 V, 50 Hz. If the voltage across the resistance is 120 V and across the coil is 200 V, calculate the power absorbed by the coil in watts.

A. 168.75 W C. 51.37 W

B. 137.5 W D. 75.31 W

248. A single phase, 7.46 kW motor is supplied from a 400 V, 50 Hz AC mains. If its efficiency is 85% and the power factor is 0.8 lagging, find the reactive component of the input current.

A. 16.46 A C. 27.43 A

B. 21.95 A D. 21 A

249. A series RLC circuit consists of 20 ohms resistance, 0.2 H inductance and an unknown capacitance. What is the value of the capacitance if the circuit has a leading angle of 45° at 60 Hz?

A. 35.18 μF C. 27.8 μF

B. 47.9 μF D. 30.7 μF

250. A 3 HP, 120 V, 60 Hz induction motor operating at 80% efficiency and 0.866 lagging power factor is to be used temporarily with 240 V, 60 Hz source. What resistance in series with the motor will be required for the motor to have 120 V across its terminals at full load?

A. 6.68 Ω C. 13.76 Ω

B. 4.77 Ω D. 9.54 Ω

251. A circuit draws a current of (3 – j8) A from a source of (100 + j37) V. Find the true power of the circuit.

A. 4 W C. 300 W

B. 596 W D. 296 W

252. A resistor and a coil are connected in series with a voltage source. If the voltage across the coil is 10 sin (866t + 70°) V and the current flowing through the resistor is 2 cos (866t – 80°) A, what is the resistance of the coil?

A. 4.92 Ω C. 5 Ω

B. 2.5 Ω D. 4.33 Ω

253. A coil has a resistance of 6 ohms and an inductance of 0.02 H. When a non-inductive resistor is connected in series with the coil, the current drawn when connected to 220 V DC source is equal to the current drawn by the coil alone across a 220 V, 60 Hz source. Determine the resistance of the non-inductive resistor.

A. 3.63 Ω C. 3.69 Ω

B. 6.39 Ω D. 3.96 Ω

254. A series RL circuit has L = 0.02 H and an impedance of 17.85 Ω. When a sinusoidal voltage is applied, the current lags the voltage by 63.5°. What is the value of the angular frequency?

A. 400 rad/sec C. 600 rad/sec

B. 500 rad/sec D. 800 rad/sec

255. A 50  resistance is connected in series with a coil having 25  resistance and 150 mH inductance. The circuit is connected to a voltage source of 200 sin t. Calculate the instantaneous current.

A. 2.9 sin t C. 2.1 sin (t – 37)

B. 1.7 sin (t + 37) D. 5.11 sin (t - 37)

256. A coil having a resistance of 25  and an inductance of 150 mH is connected in series with a 80 F capacitor across a voltage source of 200 sin 377t. What is its instantaneous current?

A. 5.84 cos (377t - 43) C. 5.84 sin (377t + 43)

B. 5.84 sin 377t D. 5.84 sin (377t - 43)

257. A coil with a 15  resistance is connected in series with a capacitor. At 60 Hz source, the impedance is measured at 15 + j11.27  while in 30 Hz source it is measured as 15 – j7.24 . Calculate the inductance of the coil.

A. 52.7 mH C. 41.2 mH

B. 65.8 mH D. 11.27 mH

258. An impedance coil has a resistance and inductance of 20 ohms and 0.05 H respectively. What value of dc voltage can be applied to the coil in order that it will take the same power from a 220 V 60 Hz mains?

(19)

B. 220 V D. 120 V

259. A ½ HP, 110 V, 60 Hz, single-phase induction motor has an efficiency of 88% and a power factor of 0.707 lagging at rated load. This motor is to be connected temporarily on a 220 V, 60 Hz line. Determine the resistance required to be placed in series with the motor in order to prevent the machine from experiencing overcurrent?

A. 25.2 ohms C. 19.5 ohms

B. 23.5 ohms D. 27.6 ohms

260. Two coils A and B known to have the same resistance are connected in series across a 110 V, 60 cycle line. The current and power delivered by the source are respectively 4.1 A and 300 W. If the voltage across coil A is twice that across coil B, calculate the inductance of coil B.

A. 8.63 mH C. 9.02 mH

B. 7.36 mH D. 4.49 mH

261. The total voltage in a series RL circuit ____ the current by an angle ____. A. lags, of 90

B. lags, between 0 and 90 C. leads, between 0 and 90

D. leads, between 90 and 180

262. In a series RL circuit, the inductor current ____ the resistor current.

A. lags C. leads

B. is equal D. is negative

263. The impedance triangle is similar to the ____ triangle with the resistance phasor in place of the ____

A. current, resistor current B. current, resistor voltage C. voltage, impedance

D. voltage, resistor voltage

264. In the impedance triangle the inductive reactance and impedance phasor are analogous to the ____ and ____ phasor respectively in the voltage triangle. A. inductive voltage, total voltage

B. inductive current, total current C. inductive voltage, resistive current D. inductive current, resistive current

265. In a series RL circuit, phasor diagram, total voltage may be represented by the ____ phasor and the resistor voltage may be represented by the ____ voltage.

A. current, voltage

B. impedance, resistance

C. current, resistance D. impedance, inductance

266. The phase angle of a series RL circuit is the angle between the ____ phasor and the ____ phasor.

A. resistance, inductive reactance B. resistance, impedance

C. inductive reactance, impedance D. none of the above

267. The phase angle of a series RL circuit may be computed ____ as ____ or ____.

A. cos-1_R/X_L_{, sin}-1_X_L_{/R, tan}-1_R/Z

B. cos-1_{R/Z, sin}-1_X

L/R, tan-1 R/XL

C. cos-1_Z/X_L_{, sin}-1_{R/Z, tan}-1_X_L_/R

D. cos-1_{R/Z, sin}-1_X_L_{/Z, tan}-1_X_L_/R

268. In the circuit of figure shown the effective value of the resistor voltage is ____ volts. 5 Ω Eeff. = 10 V 5 Ω A. √ C. √ B. 5 D. 10

269. A(n) ____ stores and returns energy to a circuit while a(n) ____ dissipates energy.

A. resistor, impedance C. inductor, resistor

B. resistor, inductor D. inductor, reactance

270. For an RL circuit, the power factor cannot be less than ____ or greater than ____.

A. 0, 1 C. 0, -1

B. 1, 0 D. –1, 0

271. The voltage across a capacitor ____ the current through it by ____.

A. lags, 45 C. leads, 0

B. lags, 90 D. leads, 90

272. If the resistance in a series RC circuit is increased the magnitude of the phase angle

(20)

A. increases B. remains the same C. decreases

D. changes to an indeterminate manner

273. In a series RC circuit, the current ____ the total voltage by an angle. A. lags, of 45

B. lags of 0

C. leads, between 0 and 90

D. leads, of 90

274. The resistance phasor for a series RC circuit points to the right. The capacitive reactance phasor points ____ while the diagonal of the rectangle having there two phasors as sides represents the ____.

A. up, impedance C. down, impedance

B. left, current D. up, total voltage

275. The phase angle for a series RC circuit is defined as the angle between the ____ and the ____ phasors.

A. current, resistance voltage B. current, total voltage

C. resistance voltage, capacitor voltage D. R, XC

276. The phase angle for a series RC circuit may be computed as the angle between the ____ and the ____ phasors.

A. resistance, impedance

B. resistance, reactance C. resistance, impedance D. none of the above

277. If a series RC circuit with 10 ohms and XC = 10 ohms carries a current of 1

ampere effective value the resistor voltage is ____ volts effective and the capacitor voltage is ____ volts effective.

A. 10/√ , 10/√ C. 10√ , 10√

B. 10, 10 D. 5, 10

278. The power dissipated in a series RL circuit with R =10 ohms and XC = 10

ohms carrying an effective current of 3 amps is ____ watts.

A. 30 C. 90

B. 30√ D. 90√

279. The magnitude of the power factor of an RC circuit with R = 10 ohms, XC =

10 ohms. I = 2 amp effective is ____.

A. 1 C. 0.707

B. 0.5 D. 0.0

280. The power dissipated in the circuit shown is ____ watts. 30 Ω

Eeff. = 100 V 40 Ω

A. 60 C. 100

B. 80 D. 120

281. The net reactance in an RLC circuit is

A. XL C. XC

B. XC – XL D. XL - XC

282. The impedance of a series RLC circuit is ____.

A. √ C. √ ( )

B. √ D. √ ( )

283. In a series RC circuit, the voltage across the capacitor and the resistor are 60 V and 80 V respectively. The input voltage should be

A. V C. V

B. V D. V 284. The transient current are due to

A. voltage applied to circuit B. resistance of the circuit C. impedance of the circuit

D. changes in stored energy in inductance and capacitance

285. To a highly inductive circuit, a small capacitance is added in series. The angle between voltage and current will

A. increase B. decrease

C. remain nearly the same D. become indeterminant

286. In a series R-L circuit. VL ____ VR by ____ degrees.

A. lags, 45 C. leads, 90

B. lags, 90 D. leads, 45

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A. arithmetic sum C. phasor sum

B. algebraic sum D. sum of the squares

288. The power in an a.c. circuit is given by

A. VI cos φ C. I² Z

B. VI sin φ D. I² XL

289. The p.f. of an R-C circuit is A. often zero

B. between zero and 1

C. always unity

D. between zero and -1.0

290. Which phasor diagram is correct for a series R-C circuit? I V I _I I V V V

Fig. 1 Fig. 2 Fig. 3 Fig. 4

A. Figure 1 C. Figure 3

B. Figure 2 D. Figure 4

291. In an R-L-C circuit, v(t) = 20 sin (314t + 5π/6) and i(t) = 10 sin (314t + 2π/3). The p.f. of the circuit is ____ and power drawn is ____ watt.

A. 0.5 lead, 200 C. 0.866 lead, 173.2

B. 0.886 lag, 186.6 D. 0.5 lag, 50

292. The input of an a.c. circuit having p.f. of 0.8 lagging is 20 kVA. The power drawn by the circuit is ____ kW.

A. 12 C. 16

B. 20 D. 8

293. The power factor of an a.c. circuit is given by A. cosine of the phase angle

B. tangent of the phase angle C. the ratio R/XL

D. the ratio XL/Z

294. In series R-L-C circuit, R = 100 Ω, XL = 300 Ω and XC = 200 Ω. The phase

angle Φ of the circuit is _____ degrees.

A. 0 C. 45

B. 90 D. -45

295. The phase angle of a series R-L-C circuit is leading if

A. XL = 0 C. XC > XL

B. R = 0 D. XC < XL

296. In an a.c. circuit, the ratio of kW/kVA represents A. power factor C. form factor

B. load factor D. diversity factor

297. If p.f. of a circuit is unity, its reactive power is

A. a maximum C. zero

B. equal to I²R D. a negative quantity

298. An R-L-C circuit has R = 10 Ω, XL = 20 Ω and XC = 30 Ω. The impedance of

the circuit is given by the expression.

A. Z = 10 + j20 C. Z = 10 – j20

B. Z = 10 + j50 D. Z = -10 + j20

299. An alternating voltage e = 200 sin 314t is applied to a device which offers an ohmic resistance of 20 Ω to the flow of current in one direction while entirely preventing the flow in the opposite direction. The average value of current will be

A. 5 A C. 1.57 A

B. 3.18 A D. 1.10 A

300. A 10 mH inductor carries a sinusoidal current of 1 A rms at a frequency of 50 Hz. The average power dissipated by the inductor is

A. 0 W C. 0.5 W

B. 0.25 W D. 1.0 W

301. A circuit component that opposes the change in circuit voltage is

A. resistance C. inductance

B. capacitance D. all of the above 302. Power loss in an electrical circuit can take place in

A. inductance only B. capacitance only

C. inductance and resistance D. resistance only

303. A circuit of zero lagging power factor behaves as A. an inductive circuit C. R-L circuit B. a capacitive circuit D. R-C circuit 304. In an R-L series circuit the power factor is

A. leading C. zero

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305. When a sinusoidal voltage is applied across an R-L series circuit having R = XL, the phase angle will be

A. 90° C. 45° leading

B. 45° lagging D. 90° leading

306. An ac source having voltage e = 110 sin (ωt + π/3) is connected in an ac circuit. If the current drawn from the circuit varies as i = 5 sin (ωt - π/3) the impedance of the circuit will be

A. 22 Ω C. 30.8 Ω

B. 16 Ω D. none of these

307. Which are of the following true of the circuit shown in the given figure? 150 V 100 Ω I VR L t 250 2 sin300 + -1. VR = √ V 2. I = 2 A 3. L = 0.25 H

Select the correct answer using the codes given below: Codes:

A. 2 and 3 C. 1 and 3

B. 1 and 2 D. 1, 2 and 3

308. The R-L circuit of the figure is fed from a constant magnitude variable frequency sinusoidal voltage source vin. At 100 Hz, the R and L element

each has a voltage drop Vrms. If the frequency of the source is changes to 50 Hz, then new voltage drop across R is

L + -vin R A. √ Vrms C. √ Vrms B. √ Vrms D. √ Vrms

309. An ac source of 200 Vrms supplies active power of 600 W and reactive power of 800 VAR. The rms current drawn from the source is

A. 10 A C. 3.75 A

B. 5 A D. 2.5 A

310. A square wave is fed to an R-C circuit. Then

A. voltage across R is square and across C is not square B. voltage across C is square and across R is not square C. voltage across both R and C is square

D. voltage across both R and C is not square

311. The voltage phasor of a circuit is V and the current phasor is A. The active and reactive powers in the circuit are

A. 10 W and 17.32 VAR

B. 5 W and 8.66 VAR C. 20 W and 60 VAR D. √ W and √ VAR

312. In a two-element series circuit, the applied voltage and resultant current are respectively, v(t) = 50 + 50 sin (5 x 103_{t) and i(t) = 11.2 sin (5 x 10}3_{t + 63.4°).}

The nature of the elements would be

A. R-L C. L-C

B. R-C D. neither R, nor L, nor C

313. A series circuit passive elements has the following current and applied voltage:

v = 200 sin (2,000t + 50°), i = 4 cos (2,000t + 13.2°) The circuit elements

A. must be resistance and capacitance B. must be resistance and inductance

C. must be inductance, capacitance and resistance

D. could be either resistance and capacitance or resistance, inductance and capacitance

314. A two terminal black box contains one of the R-L-C elements. The black box is connected to a 220 V ac supply. The current through the source is I. When a capacitance of 0.1 F is inserted in series between the source and the box, the current through the source is 2I. The element is

A. a resistance B. an inductance

C. a capacitance

D. it is not possible to determine the element 315. In the following circuit, i(t) under steady state is

i(t) 2 H 1 F 1 Ω

10 sin t 5 V

(23)

A. zero C. 7.07 sin t

B. 5 D. 7.07 sin (t – 45°)

316. The source in the circuit is a sinusoidal source. The supply voltages across various elements are marked in the figure. The input voltage is

14 V 10 V 3 V

A. 10 V C. 27 V

B. 5 V D. 24 V

317. In the circuit shown in the given figure, if the power consumed by the 5 Ω resistor is 10 W, then the pf of the circuit is

L 5 Ω 50 cos ωt 10 Ω A. 0.8 C. 0.5 B. 0.6 D. zero

318. In an RL circuit, supplied from an ac source, the reactive power is proportional to the

A. the average energy stored in the electric field B. the average energy stored in the magnetic field

C. sum of the average energy stored in the electric field and that stored in the magnetic field

D. difference of the average energy stored in the electric field and that stored in the magnetic field

319. If a series RLC circuit excited by a voltage e = E sin ωt when LC < 1/ω2

A. current lags behind the applied voltage B. current leads the applied voltage

C. current is in phase with the applied voltage D. voltage across L and C are equal

320. The current in the circuit shown is

A. 5 A C. 15 A

B. 10 A D. 25 A

321. In the case of the R-L-C circuit shown in the given figure, the voltage across the R, L and C would be respectively

15 V (rms) R L C V1 V2 20 V (rms) _{9 V (rms)} A. 12 V, 16 V and 7 V or 25 V B. 16 V, 12 V and 7 V or 25 V C. 7 V, 16 V and 12 V D. 16 V, 12 V and 25 V

322. Consider the following statements regarding the circuit shown in the figure.

I 10 6 V

5 Ω j15 / 3 _{10 Ω}

If the power consumed by 5 Ω resistor is 10 W then 1. |I| = √ A

2. the total impedance of the circuit is 5 Ω 3. cos θ = 0.866

Which of these statements is correct?

A. 1 and 3 C. 1 and 2

B. 2 and 3 D. 1, 2 and 3

323. In an ac circuit if voltage V = (a + jb) and current I = (c + jd), then the power is given by

A. ac + ad C. bc - ad