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- Question
For a BJT a = 0.98, then ? =
Options- A. 0.02
- B. 0.5
- C. 4.9
- D. 48
- Correct Answer
- 48
Explanation
Power Electronics problems
Search Results
- 1. Assertion (A): Inverters and choppers use fast switching thyristors
Reason (R): Fast switching SCR has low turn off time.
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 Discuss
Correct Answer: Both A and R are correct and R is correct explanation of A
Explanation:
Low turn off time enables fast switching.- 2. A semiconverter feeding an RLE load operates in
Options- A. first quadrant only
- B. first and second quadrants
- C. first and fourth quadrants
- D. first and third quadrants Discuss
Correct Answer: first quadrant only
Explanation:
Semiconvertor operates only in first quadrant.- 3. A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current
Options- A. are similar
- B. are not similar
- C. may be similar or dissimilar
- D. are similar only if firing angle is zero Discuss
Correct Answer: are not similar
Explanation:
When freewheeling diode conducts output current exists but output voltage is zero.- 4. The phenomenon of overlap in converter operation due to
Options- A. source resistance
- B. source inductance
- C. both source resistance and source inductance
- D. high value of firing angle Discuss
Correct Answer: source inductance
Explanation:
Source inductance delays turn off and hence causes overlap.- 5. Assertion (A): A transistor requires a continuous base signal for conduction but a thyristor requires a gate pulse.
Reason (R): Transistor find widespread application in power electronic circuits.
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 Discuss
Correct Answer: A is correct but R is wrong
Explanation:
Transistors are used but not very widely.- 6. The terminals of a power BJT are called
Options- A. emitter, base, collector
- B. emitter, base, drain
- C. source, base, drain
- D. source, base, collector Discuss
Correct Answer: emitter, base, collector
Explanation:
In a BJT terminals are emitter, base and collector irrespective of rating.- 7. In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is
Options- A. p - a
- B. p
- C. p + a
- D. p - 2a Discuss
Correct Answer: p
Explanation:
Since conduction is from a to p + a, period of conduction is p in each half cycle.- 8. A semi converter operates in two quadrants.
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
It operates only in quadrant.- 9. Figure shows a chopper feeding RLE load, The free wheeling diode conducts when
Options- A. thyristor is on
- B. thyristor is off
- C. both when thyristor is on and thyristor is off
- D. partly when thyristor is off and partly when thyristor is on Discuss
Correct Answer: thyristor is off
Explanation:
FD is forward biased only when thyristor is off.- 10. A chopper
Options- A. converts constant voltage dc into ac and then into variable voltage dc
- B. converts constant voltage dc into variable voltage dc directly
- C. converts ac of one frequency into ac of another frequency
- D. converts ac to dc Discuss
Correct Answer: converts constant voltage dc into variable voltage dc directly
Explanation:
A chopper is a dc-ac converter. It converts a fixed dc voltage into a variable dc voltage.
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- 1. Assertion (A): Inverters and choppers use fast switching thyristors