MCQ in Power Electronics Part 2 | ECE Board Exam

This is the Multiple Choice Questions Part 2 of the Series in Power Electronics as one of the Electronics Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electronics Engineering field, Electronics Books, Journals and other Electronics References.

Continue Practice Exam Test Questions Part 2 of the Series

⇐ MCQ in Power Electronics Part 1 | ECE Board Exam

Choose the letter of the best answer in each questions.

51. Anode of an operational SCR is

A. Always positive w.r.t cathode

B. Always negative w.r.t anode

C. Always positive w.r.t anode

D. Always negative w.r.t cathode

52. If the gate voltage of an SCR is removed, then the

A. anode current decreases

B. anode current does not decrease at all

C. anode current increases

D. cathode current increases

53. In a single-phase full wave rectifier, during blocking state the peak inverse voltage of diode is

A. Vm

B. 2 Vm

C. Vm/2

D. 4 Vm

54. In a full wave rectifier, the rectification ratio is approximately equal to

A. 61%

B. 71%

C. 81%

D. 91%

55. For power output higher than 15 kW, the suitable rectifier is

A. Single phase

B. 3 phase

C. Poly phase

D. Only (b) and (c)

56. The sum of all phase current in a star connected primary winding with no neutral connection is equal to

A. Phase current

B. Three times the phase current

C. Three times the line current

D. Zero at all times

57. In a 3-phase bridge rectifier the ripple frequency is

A. Equal to the input frequency

B. Twice the input frequency

C. Three times the input frequency

D. Six times the input frequency

58. DIAC are specifically designed to trigger

A. TRIAC

B. SCR

C. GTO

D. Only (a) and (b)

59. As the breakdown voltage reached, the DIAC exhibits

A. Negative resistance characteristics

B. Goes into avalanche condition

C. Voltage drop snaps back

D. All of these

60. In BJT, the forward biased base emitter junction injects holes from base to emitter, the holes

A. Do not contribute to the collector current

B. Result in net current flow component into the base

C. Contribute to the collector current

D. Only (a) and (b)

61. In BJT, switching losses occurs

A. Only at turn – on

B. Only at turn – off

C. Both at turn on and off

D. None of these

62. Choppers is a

A. AC – DC converters

B. AC – AC converters

C. DC – AC converters

D. DC – DC converters

63. The average value of the output voltage in a step – down dc chopper is given by

A. V 0 = Vs

B. V 0 = D Vs

C. V 0 = Vs / D

D. V 0 = Vs / ( 1 – D )

64. The voltage will be

A. 230 V

B. 250 V

C. 275 V

D. 325 V

65. The dc current will be approximately

A. 2.5 A

B. 3 A

C. 3.25 A

D. 3.75 A.

66. The ac input current at slip rings will be

A. 6.3 A

B. 5.8 A

C. 4.1A

D. 3.8 A.

67. For 3 phase rotary converters, when power factor is unity. the ac line to dc current ratio is

A. 1.5

B. 1.1

C. 1.0

D. 0.942.

68. In an arc rectifier the drop in voltage at the cathode is approximately

A. 1 volt

B. 6 to 7 volts

C. 60 to 70 volts

D. 1.2 V7 volts.

69. In arc rectifiers mercury is chosen as the liquid for rectifier because

A. it has low specific heat

B. it has low ionization potential

C. it has high atomic weight

D. all of the above.

70. Ionization potential of mercury is approximately

A. 1 V

B. 2 V

C. 10.4 V

D. 104 V.

71. Least undulating current will be delivered by which mercury arc rectifier

A. 1-phase

B. 2 phase

C. 3 phase

D. 6 phase.

72. In a mercury arc rectifier the cathode voltage drop is due to

A. surface resistance

B. expenditure of energy in liberating electrons from the mercury

C. expenditure of energy in ionization

D. expenditure of energy in overcoming the electrostatic field.

73. In mercury arc rectifier, voltage drop at anode is due to

A. energy spent in overcoming the electrostatic field

B. high temperature inside the rectifier

C. self-restoring property of mercury

D. high ionization potential.

74. The average life of the glass bulb rectifier is

A. 100 to 150 hours

B. 1000 to 1500 hours

C. 10,000 to 15,000 hours

D. 100,000 to 150,000 hours.

75. The vacuum inside the glass bulb of a mercury arc rectifier is of the order of

A. 5 x 10^-3 cm of Hg

B. 5 x 10^-4 cm of Hg

C. 5 x 10^-5 cm of Hg

D. 5 x 10^-8 cm of Hg.

76. For mercury arc rectifiers, the anode is usually made of

A. Aluminium

B. Copper

C. Tungsten

D. Graphite.

77. In a phase controlled 3 phase ac voltage controller, the harmonic present is

A. 2

B. 3

C. 5

D. 7

78. The maximum firing angle in the half wave-controlled regulator is

A. 180 degree

B. 190 degree

C. 200 degree

D. 210 degree

79. The on – state voltage drop of IGBT consists of

A. Drop across the collector junction

B. Drop across the drift region

C. Drop across MOSFET portion

D. All of these

80. To detect an over – current fault condition, the most reliable method is to connect a

A. Current sensor across IGBT

B. Voltage sensor across IGBT

C. Current sensor in series with IGBT

D. Voltage sensor in series with IGBT

81. The IGBT resulted in higher switching speed and lower energy losses. It can be used for

A. Uninterruptible power supplies

B. Induction heating system

C. Constant voltage and frequency power supplies

D. All of these

82. An ideal diode is

A. Unidirectional

B. Bidirectional

C. Fixed voltage polarity

D. Only (a) and (c)

83. Bidirectional semiconductor device is

A. Diode

B. BJT

C. SCR

D. TRIAC

84. With gate open, the maximum anode current at which SCR is turned off from ON condition is called

A. breakdown voltage

B. peak reverse voltage

C. holding current

D. latching current

85. The curve between V and I of SCR when anode is positive w.r.t cathode and when anode is negative w.r.t cathode are known as

A. both as forward characteristics

B. both as reverse characteristics

C. former as forward characteristics and later as reverse characteristics

D. former as reverse characteristics and later as forward characteristics

86. Form factor of a rectifier is the ratio of

A. Root mean square value of voltage and current to its peak value

B. Root mean square value of voltage and current to its average value

C. Average value of current and voltage to its root mean square value

D. Peak value of current and voltage to its root mean square value

87. Ripple factor is the ratio of

A. Rms value of the ac component of load voltage to the dc voltage

B. Average value of the ac component of load voltage to the peak value of voltage

C. Average value of the dc component of load voltage to the ac voltage

D. Peak value of the dc component of load voltage to the ac voltage

88. Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of

A. AC input power to the transformer volt – amp rating required by secondary

B. AC input power to the transformer volt – amp rating required by primary

C. DC output power to the transformer volt – amp rating required by secondary

D. DC output power to the transformer volt – amp rating required by primary

89. Which of the following finds application in speed control of a dc motor?

A. FET

B. NPN transistor.

C. SCR.

D. None of the above.

90. In mercury arc rectifiers the voltage drop in arc is nearly

A. 0.1 volt per centimeter of arc length

B. 1 volt per centimeter of arc length

C. 10 volts per centimeter of arc length

D. 12 to 15 volts per centimeter of arc length.

91. A cycloconverter is a _________

A. one stage power converter

B. one stage voltage converter

C. one stage frequency converter

D. none of the mentioned

92. Applications of cycloconverters include

A. speed control of ac drives

B. induction heating

C. static VAr compensation

D. all of the mentioned

93. The single-phase mid-point type cycloconverter uses __________ number of SCRs.

A. 4

B. 8

C. 6

D. none of the mentioned

94. The single-phase bridge type cycloconverter uses __________ number of SCRs.

A. 4

B. 8

C. 6

D. none of the mentioned

95. The principle of three phase cycloconverter is to

A. add and remove number of SCRs

B. vary progressively the firing angle of the devices

C. keep the firing angle as 0° for all the devices

D. none of the mentioned

96. In three phase cycloconverters, the reduction factor is given by

A. input frequency/output frequency

B. (input frequency/output frequency) -1

C. (input frequency/output frequency) -1/2

D. (input frequency/output frequency) 1/2

97. In a three phase half-wave cycloconverter ___________

A. both inverting and converting action takes place

B. only inversion action takes place

C. only converting action takes place

D. none of the mentioned

98. In the ___________ type of chopper, two stage conversions takes place.

A. AC-DC

B. AC link

C. DC link

D. None of the mentioned

99. Choppers converter

A. AC to DC

B. DC to AC

C. DC to DC

D. AC to AC

100. A chopper may be thought as a

A. Inverter with DC input

B. DC equivalent of an AC transformer

C. Diode rectifier

D. DC equivalent of an induction motor

Complete List of MCQ in Electronics Engineering per topic