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MCQOPTIONS
This section includes 657 Mcqs, each offering curated multiple-choice questions to sharpen your Testing Subject knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A single phase step up cycloconverter changes 50 Hz to 100 Hz. Then one half wave of input will give rise to |
| A. | one half wave of output |
| B. | one full wave of output |
| C. | two full waves of output |
| D. | either (b) or (c) |
| Answer» C. two full waves of output | |
| 2. |
Mc Murray full bridge inverter uses |
| A. | 8 thyristors and 4 diodes |
| B. | 8 thyristors and 8 diodes |
| C. | Both A and R are correct and R is correct explanation of A |
| D. | Both A and R correct but R is not correct explanation of A |
| Answer» D. Both A and R correct but R is not correct explanation of A | |
| 3. |
In the basic series inverter circuit, the source current has |
| A. | low harmonic content |
| B. | high harmonic content |
| C. | low or high harmonic content depending on firing angle |
| D. | zero harmonic content |
| Answer» C. low or high harmonic content depending on firing angle | |
| 4. |
Assertion (A): Snubber circuit has an RC series circuit in parallel with SCRReason (R): Voltage across a capacitor can not change instantaneously. |
| 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 |
| Answer» B. Both A and R correct but R is not correct explanation of A | |
| 5. |
When UJT is used for thyristor gate signal, the output of UJT is |
| A. | sine wave |
| B. | square wave |
| C. | saw tooth wave |
| D. | either (a) or (c) |
| Answer» D. either (a) or (c) | |
| 6. |
Assertion (A): The turn on time of SCR is about 1 to 4 ms.Reason (R): The turn off time of SCR is about 10 to 300 ms. |
| 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 |
| Answer» C. A is correct but R is wrong | |
| 7. |
In pulse width modulation of chopper |
| A. | T is kept constant and Ton is varied |
| B. | Ton is kept constant T is varied |
| C. | both T and Ton are varied |
| D. | either T or Ton is varied |
| Answer» B. Ton is kept constant T is varied | |
| 8. |
A half bridge inverter |
| A. | needs a 3 wire dc supply |
| B. | may use a two wire or 3 wire dc supply |
| C. | has higher output voltage if fed from 3 wire dc supply |
| D. | has higher efficiency if fed from 3 wire dc supply |
| Answer» B. may use a two wire or 3 wire dc supply | |
| 9. |
Modified Mc Murray full bridge inverter uses |
| A. | 4 thyristors and 2 diodes |
| B. | 4 thyristors and 4 diodes |
| C. | 8 thyristors and 4 diodes |
| D. | 8 thyristors and 8 diodes |
| Answer» E. | |
| 10. |
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torque |
| A. | will be less than 100 N-m |
| B. | will be more than 100 N-m |
| C. | may be more or less than 100 N-m depending on motor parameters |
| D. | very small |
| Answer» C. may be more or less than 100 N-m depending on motor parameters | |
| 11. |
The two-transistor model of a thyristor consists of two transistors : |
| A. | one n-p-n and other p-n-p |
| B. | both p-n-p |
| C. | both n-p-n |
| D. | one n-p-n and other UJT |
| Answer» B. both p-n-p | |
| 12. |
An SBS can conduct is one direction only. |
| A. | 1 |
| B. | |
| C. | 3 |
| D. | 4 |
| Answer» C. 3 | |
| 13. |
A single phase dual converter consists of |
| A. | two fully controlled converters connected in parallel |
| B. | two fully controlled converters connected in antiparallel |
| C. | two fully controlled semiconverters connected in antiparallel |
| D. | two fully controlled semiconverters connected in parallel |
| Answer» C. two fully controlled semiconverters connected in antiparallel | |
| 14. |
The main utility of SCR is due to |
| A. | gate triggering |
| B. | high temperature triggering |
| C. | triggering |
| D. | high breakdown voltage |
| Answer» B. high temperature triggering | |
| 15. |
The number of gates in an SCR is |
| A. | 1 |
| B. | 3 |
| C. | 4 |
| D. | 6 |
| Answer» B. 3 | |
| 16. |
A cycloconverter is |
| A. | ac-dc converter |
| B. | dc-ac converter |
| C. | dc-dc converter |
| D. | ac-ac converter |
| Answer» E. | |
| 17. |
A single phase semiconverter is supplying RLE load and has a freewheeling diode across the load. The firing angle is a. The freewheeling diode conducts for |
| A. | a° in each half cycle |
| B. | (p - a)° in each cycle |
| C. | a° in one full cycle |
| D. | (p + a)° in each half cycle |
| Answer» B. (p - a)¬∞ in each cycle | |
| 18. |
In a dual converter operated in circulating current mode, the circulating current flows |
| A. | when load current is zero |
| B. | when load current is non-zero |
| C. | even when load current is zero |
| D. | none of the above |
| Answer» D. none of the above | |
| 19. |
A single phase semiconverter is feeding a highly inductive load. The circuit has a freewheeling diode across the load and firing angle is a. During one cycle of input voltage, the total duration of conduction of freewheeling diode is |
| A. | a |
| B. | 0.083333333333333 |
| C. | 0.16666666666667 |
| D. | 0.5 a |
| Answer» C. 0.16666666666667 | |
| 20. |
In a bridge inverter |
| A. | an output transformer is essential |
| B. | an output transformer is not essential |
| C. | an output transformer cannot be connected |
| D. | an output transformer, if used, can improve the efficiency of the circuit |
| Answer» C. an output transformer cannot be connected | |
| 21. |
In thermal ohm's law, temperature and power loss are analogous to |
| A. | V and I respectively of ohm's law |
| B. | I and V respectively of ohm's law |
| C. | R and V respectively of ohm's law |
| D. | I and R respectively of ohm's law |
| Answer» C. R and V respectively of ohm's law | |
| 22. |
Assertion (A): An ac regulator uses natural commutationReason (R): An ac regulator can be used for static on load tap changing of transformer. |
| 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 |
| Answer» C. A is correct but R is wrong | |
| 23. |
In load commutated chopper, the commutating element |
| A. | is capacitor, inductor and auxiliary thyristor |
| B. | any of the above depending on load |
| C. | 2 f |
| D. | f |
| Answer» B. any of the above depending on load | |
| 24. |
Assertion (A): A GTO circuit is more compact than SCR circuit Reason (R): A GTO can be turned off by negative gate pulse. |
| 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 |
| Answer» B. Both A and R correct but R is not correct explanation of A | |
| 25. |
The circuit in figure is for |
| A. | resonant commutation |
| B. | self commutation |
| C. | load commutation |
| D. | auxiliary commutation |
| Answer» C. load commutation | |
| 26. |
Which of these commutation methods uses an external pulse for commutation? |
| A. | Class A |
| B. | Class C |
| C. | Class E |
| D. | Class F |
| Answer» D. Class F | |
| 27. |
Forward rating of an SCR is |
| A. | the maximum rate of rise of anode voltage which will not trigger the SCR if gate signal is not applied |
| B. | either (b) or (c) |
| C. | 2 |
| D. | 3 |
| Answer» D. 3 | |
| 28. |
In an ordinary thyristor |
| A. | turn on and turn off times are equal |
| B. | turn on time is more than turn off time |
| C. | turn off time is more than turn on time |
| D. | turn on time may be equal, less than or more than turn off time |
| Answer» D. turn on time may be equal, less than or more than turn off time | |
| 29. |
Which of the following devices has metal-silicon junction? |
| A. | General purpose power diode |
| B. | Schottky diode |
| C. | SCR |
| D. | MOSFET |
| Answer» C. SCR | |
| 30. |
A static induction thyristor |
| A. | is a majority carrier device |
| B. | is a minority carrier device |
| C. | either a majority carrier or minority carrier device |
| D. | has a total number of 2 leads |
| Answer» C. either a majority carrier or minority carrier device | |
| 31. |
Typical values of for an SCR are in the range of |
| A. | 1 to 10 |
| B. | 25 to 500 |
| C. | 0.1 to 1 |
| D. | 1000 to 2000 |
| Answer» C. 0.1 to 1 | |
| 32. |
The output frequency of a cycloconverter can be changed by changing the firing angle. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 33. |
In the circuit of figure, the load current when thyristor is off |
| A. | is constant |
| B. | increases exponentially |
| C. | decreases exponentially |
| D. | zero |
| Answer» D. zero | |
| 34. |
In a single phase full wave ac regulator, the firing angles in the two half cycles |
| A. | are always equal |
| B. | are sometimes equal |
| C. | are never equal |
| D. | may be equal or unequal |
| Answer» B. are sometimes equal | |
| 35. |
A surge voltage |
| A. | has very high magnitude and very long duration |
| B. | has very high magnitude and very small duration |
| C. | has very high magnitude and very small duration and can be positive or negative |
| D. | can be only positive |
| Answer» D. can be only positive | |
| 36. |
The number of leads in a DIAC are |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 6 |
| Answer» B. 3 | |
| 37. |
All inverters use forced commutation. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 38. |
In auxiliary commutated chopper, the charging and discharging time of capacitor |
| A. | are constant |
| B. | depend on load current |
| C. | may be constant or may depend on load current |
| D. | none of the above |
| Answer» C. may be constant or may depend on load current | |
| 39. |
In a single phase full wave ac regulator the firing angles during both half cycles are equal. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 40. |
Present day HVDC converters are all |
| A. | 3 pulse converters |
| B. | 6 pulse converters |
| C. | 12 pulse converters |
| D. | either 6 pulse or 12 converters |
| Answer» D. either 6 pulse or 12 converters | |
| 41. |
In an SCR, the anode current consists of |
| A. | only holes |
| B. | only electrons |
| C. | both electrons and holes |
| D. | either electrons or holes |
| Answer» D. either electrons or holes | |
| 42. |
Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V. Reason (R): When an SCR is conducting, the junction temperature is about 200°C. |
| 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 |
| Answer» D. A is wrong but R is correct | |
| 43. |
The difference between resonant commutation and self commutation is |
| A. | both these methods are based on entirely different principles |
| B. | in resonant commutation, the commutating elements carry load current but in self commutation, the commutating elements do not carry load current |
| C. | resonant commutation uses L and C but self commutation uses only capacitor |
| D. | none of the above |
| Answer» B. in resonant commutation, the commutating elements carry load current but in self commutation, the commutating elements do not carry load current | |
| 44. |
A UJT exhibits negative resistance characteristics when |
| A. | Current is less than valley current |
| B. | Current is less than peak current |
| C. | Current is more than peak current but less than valley current |
| D. | None of the above |
| Answer» D. None of the above | |
| 45. |
A class A chopper has an input voltage of 200 V. Ton = 1.5 ms and Toff = 4.5 ms. The duty cycle, average output voltage and ripple factor respectively are |
| A. | 0.5, 100 V and 1 |
| B. | 0.25, 50 V and 3 |
| C. | 0.25, 50 V and 1 |
| D. | 0.5, 100 V and 3 |
| Answer» C. 0.25, 50 V and 1 | |
| 46. |
Between which points does UJT exhibit negative resistance characteristics |
| A. | between peak and valley points |
| B. | before peak point |
| C. | after peak point |
| D. | after valley point |
| Answer» B. before peak point | |
| 47. |
Which of these devices can conduct in both directions? |
| A. | SCR |
| B. | SUS |
| C. | SBS |
| D. | UJT |
| Answer» D. UJT | |
| 48. |
A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 Ω per phase. The peak value of load current is |
| A. | 40 A |
| B. | 20 A |
| C. | 0.41666666666667 |
| D. | 0.20833333333333 |
| Answer» C. 0.41666666666667 | |
| 49. |
In a 3 phase full converter feeding a highly inductive load, the average load current is 150 A. The peak current through thyristor is |
| A. | 150 A |
| B. | 75 A |
| C. | 50 A |
| D. | 300 A |
| Answer» B. 75 A | |
| 50. |
A dc series motor is coupled to a load whose torque is proportional to speed. It is fed by a single phase ac supply through a full converter. When speed is 500 rpm, firing angle is 45°. It is desired to raise the speed. It will be necessary to |
| A. | decrease the firing angle |
| B. | increase the firing angle |
| C. | either decrease or increase the firing angle depending on the required speed |
| D. | decrease the load torque |
| Answer» B. increase the firing angle | |