power electronics MCQs – Page 6

Practise focused power electronics questions with marked answers for exam preparation and subject revision.

power electronics Mcqs
101. Very large values of modulation index (greater than 3.24) lead to___________?
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A. Sine AC output voltage

B. Square AC output voltage

C. Trapezoidal AC output voltage

D. Triangular AC output voltage

102. ON state voltage drop across SCR lie between the range_____________?
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A. 1 1.5 V.

B. 0.5 1 V.

C. 1.5 2 V.

D. 0 0.5 V.

103. In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes__________________?
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A. Zero

B. Negative

C. Positive

D. None of these

104. Snubber circuit is used with SCR_________________?
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A. either series or parallel

B. in series

C. in parallel

D. anti parallel

105. For swept frequency measurements, the input impedance of the mismatched transmission line would vary with frequency as the electrical length of the transmission line would
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A. Increase with frequency

B. Decrease with frequency

C. Either A. or B.

D. Remains same with change in frequency

106. In BJT, switching losses occurs___________?
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A. Only at turn on

B. Only at turn off

C. Both at turn on and off

D. None of these

107. Silicon controlled rectifier can be turned on____________?
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A. By applying a gate pulse and turned off only when current becomes zero

B. By making current non zero and turned off by making current zero

C. And turned off by applying gate pulse

D. By applying a gate pulse and turned off by removing the gate pulse

108. If a shunt motor is started with its field winding open then___________?
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A. None of these

B. It will rotate at dangerously high speed

C. It will rotate at less speed as that with its field winding closed

D. It will rotate at the same speed as that with its field winding closed

109. Advantages of HVDC transmission over AC system is / are____________?
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A. Reversal of power can be controlled by firing angle

B. They can link two AC system operating unsynchronized

C. All of these

D. Very good dynamic behavior

110. Thyristor can be protected from over voltages by using
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A. 23 mA.

B. 60 mA.

C. 40 mA.

D. 10 mA.
111. Let of a thyristor Vc1, Vc2, Vc3 are forward break over voltage for gate current Ig1, Ig2, Ig3 respectively. Then________________?
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A. Vc1 > Vc2 > Vc3 when Ig1 < Ig2 < Ig3.

B. Vc1 = Vc2 = Vc3 any value of Ig.

C. Vc1 > Vc2 > Vc3 when Ig1 > Ig2 > Ig3.

D. Vc1 > Vc2 > Vc3 when Ig1 aYEN Ig2 &Atil

112. Compared to transistor, _________ have lower on state conduction losses and higher power handling capability?
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A. MOSFETs

B. Thyristor

C. Semi conductor diodes

D. TRIACs

113. The power MOSFET device is a___________?
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A. Current controlled bipolar device

B. Voltage controlled unipolar device

C. Voltage controlled bipolar device

D. Current controlled unipolar device

114. Choppers is a_______________?
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A. DC AC converters

B. DC DC converters

C. AC DC converters

D. AC AC converters

115. During which time maximum conduction spreading take place in the thyristor during turn ON?
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A. Rise time

B. Delay time

C. Spread time

D. Same for every case

116. An SCR can be used___________?
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A. All of these

B. as static conductor

C. for speed control of dc shunt motor

D. for power control

117. The switching function of semiconductor devices can be characterized with___________?
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A. Duty ratio only

B. Duty ratio and frequency

C. Frequency only

D. Duty ratio, frequency and time delay
118. A power MOSFET has three terminals called___________?
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A. Collector, emitter and gate

B. Drain, source and base

C. Drain, source and gate

D. Collector, emitter and base

119. The opposite of susceptibility is___________?
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A. Interference

B. Electromagnetic compatibility

C. Emission

D. Immunity
120. A capacitive load in voltage source inverters generates ________________?
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A. Small current spikes and can be increased by using an inductive filter

B. Small current spikes and can be reduced by using an inductive filter

C. Large current spikes and can be increased by using an inductive filter

D. Large current spikes and can be reduced by using an inductive filter