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Power Electronics problems

1. Assertion (A): The circuit of figure thyristor will conduct for 180� during positive half cycle if it is continuously fired.

Reason (R): A thyristor can conduct only when it is forward biased.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

2. The effect of source inductance in a 3 phase fully controlled bridge converter is to
Options
A. decrease the output voltage
B. increase the output voltage
C. decrease the output voltage and increase the output current
D. increase the output voltage and decrease the output current

3. Class A and class B chopper
Options
A. operate in first quadrant
B. operate in second quadrant
C. class A chopper operates in first quadrant while class B operates in second quadrant
D. may operate in either first or second quadrant

4. In a modified series inverter
Options
A. the maximum output frequency is less than frequency of damped oscillations
B. the output frequency can be even higher than the frequency of damped oscillations
C. the output frequency cannot exceed the frequency of damped oscillations
D. any of the above

8. When an SCR is reverse biased
Options
A. two junctions are reverse biased and one junction is forward biased.
B. all the three junctions are reverse biased.
C. one junction is reverse biased and two junctions are forward biased.
D. any of the above depending on the magnitude of reverse bias.

9. From which instant is the turn off time of a thyristor defined
Options
A. when anode voltage becomes zero
B. when anode current becomes zero
C. when both anode voltage and current become zero
D. none of the above

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