Power electronics MCQ #2

1) The V-I Characteristics of the diode lie in the

      (a) 1st & 4th quadrant

      (b) 1st & 3rd quadrant

      (c) 1st & 2nd quadrant

      (d) Only in the 1st quadrant

2) A diode is said to be forward biased when the

      (a) anode is positive with respect to the cathode

      (b) cathode is positive with respect to the anode

      (c) anode is negative with respect to the anode

      (d) both cathode & anode are positive

3) In an AC-DC converter, a diode might be used as a

      (a) filter

      (b) phase angle controller

      (c) freewheeling Diode

      (d) voltage source

4) Which of the following diodes uses a metal-semiconductor junction?

      (a) Fast recovery diodes

      (b) General purpose diodes

      (c) None of the mentioned

      (d) Schottky diode

5) A Schottky diode has __________

      (a) aluminum-silicon junction

      (b) a gate terminal

      (c) germanium-Arsenide junction

      (d) platinum gold junction

ANSWER: | 1-b| 2-a | 3-c | 4-d | 5-a |

6) The time constant of a series RL circuit (τ) is given by

      (a) L/R

      (b) R/L

      (c) 1/RL

      (d) RC

7) Choppers converter

      (a) DC to AC

      (b) AC to DC

      (c) AC to AC

      (d) DC to DC

8) What is the duty cycle of a chopper?

      (a) Ton/T

      (b) Ton/Toff

      (c) Toff x Ton

      (d) T/Ton

9) The load voltage of a chopper can be controlled by varying the

      (a) reactor position

      (b) firing angle

      (c) duty cycle

      (d) extinction angle

10) In a 3-phase full converter using six SCRs, gating circuit must provide

      (a) one firing pulse every 90°

      (b) one firing pulse every 30°

      (c) three firing pulses per cycle

      (d) one firing pulse every 60°

ANSWER: | 6-b | 7-d | 8-a | 9-c | 10-d |

11) The major function of the pulse transformer is to

      (a) increase the voltage amplitude

      (b) create periodic pulses

      (c) isolate low & high-power circuit

      (d) reduce harmonics

12) The shape of the output voltage waveform in a single PWM is

      (a) triangular wave

      (b) square wave

      (c) sine wave

      (d) quasi-square wave

13) The distortion factor is 

      (a) total RMS output voltage / RMS value of all the harmonic components

      (b) fundamental RMS output voltage / fundamental average output voltage

      (c) total RMS output voltage / fundamental RMS output voltage

      (d) fundamental RMS output voltage / total RMS output voltage

14) A three-phase bridge inverter requires minimum of _____________ switching devices.

      (a) 6

      (b) 4

      (c) 3

      (d) 8

15) Leakage current flows through the thyristor in

     (a) forward blocking mode.

     (b) reverse blocking mode.

     (c) both forward and reverse blocking mode.

     (d) forward conduction mode.

ANSWER: | 11-c | 12-d | 13-d | 14-a | 15-c |

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