MCQOPTIONS
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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. |
In a full bridge inverter, the waveshape of load current depends on |
| A. | relative values of load parameters R, L and C |
| B. | relative values of load parameters R and L |
| C. | relative values of load parameters L and C |
| D. | gating frequency |
| Answer» B. relative values of load parameters R and L | |
| 2. |
A NAND gate has 3 inputs and one output. The number of thyristors required for this gate are |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 3 or 4 |
| Answer» D. 3 or 4 | |
| 3. |
In the basic series inverter circuit, the source supplies load |
| A. | only in positive half cycle |
| B. | both in positive and negative half cycles |
| C. | only in part of positive half cycle |
| D. | in positive half cycle and part of negative half cycle |
| Answer» B. both in positive and negative half cycles | |
| 4. |
In a full wave converter (M - 2 connection) feeding an RLE load, the peak thyristor current is 15 A. For fully controlled bridge circuit and same load current, the peak thyristor current will be |
| A. | 30 A |
| B. | 152 A |
| C. | 15 A |
| Answer» D. | |
| 5. |
The snubber circuit consists of |
| A. | a capacitor connected in series with thyristor |
| B. | a capacitor connected in parallel with thyristor |
| C. | a resistor and capacitor in series connected across thyristor |
| D. | none of the above |
| Answer» D. none of the above | |
| 6. |
A cycloconverter uses |
| A. | natural commutation |
| B. | forced commutation |
| C. | either natural or forced commutation |
| D. | both natural and forced commutation together |
| Answer» D. both natural and forced commutation together | |
| 7. |
When an SCR is reverse biased |
| 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. |
| Answer» B. all the three junctions are reverse biased. | |
| 8. |
In a multiphase chopper, the different choppers operate in |
| A. | series and all simultaneously |
| B. | parallel and one at a time |
| C. | parallel and simultaneously |
| D. | either (b) or (c) |
| Answer» C. parallel and simultaneously | |
| 9. |
A dc chopper feeds an RLE load and has a duty cycle of 1. The load current will be such that |
| A. | |
| B. | Imax > Imin |
| C. | Imin > 0 |
| Answer» B. Imax > Imin | |
| 10. |
Assertion (A): A cycloconverter may be line commutated or forced commutatedReason (R): A step up cycloconverter requires forced commutation. |
| 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 | |
| 11. |
The factor η for a UJT is about |
| A. | 0.1 |
| B. | 0.2 |
| C. | 0.6 |
| D. | 0.9 |
| Answer» D. 0.9 | |
| 12. |
If we connect two silicon unilateral switches in anti- parallel we get |
| A. | SCR |
| B. | SBS |
| C. | SCS |
| D. | UJT |
| Answer» C. SCS | |
| 13. |
A separately excited dc motor is run from a dc source through a chopper. At 600 rpm and rated torque, the duty cycle of chopper is 0.8. At 600 rpm and half the rated torque, the duty cycle is likely to be |
| A. | 0.9 |
| B. | 0.8 |
| C. | 0.75 |
| D. | 0.6 |
| Answer» D. 0.6 | |
| 14. |
A load commutated chopper circuit has |
| A. | one thyristor |
| B. | two thyristors |
| C. | four thyristors |
| D. | six thyristors |
| Answer» D. six thyristors | |
| 15. |
In a 3 phase semiconverter, the freewheeling diode comes into operation only if firing angle |
| A. | is zero |
| B. | is 60° |
| C. | is more than 60° |
| D. | is more than 90° |
| Answer» D. is more than 90¬∞ | |
| 16. |
A full bridge inverter is fed by a battery of 30 V. The rms value of output voltage is |
| A. | 15 V |
| B. | 152 V |
| C. | 30 V |
| D. | 302 V |
| Answer» D. 302 V | |
| 17. |
In a modified series inverter with two inductors and two capacitors, the load current |
| A. | has 2 parallel paths |
| B. | has only one parallel path |
| C. | can have three parallel paths |
| D. | has four parallel paths |
| Answer» B. has only one parallel path | |
| 18. |
A single phase series converter is used for |
| A. | high voltage output |
| B. | high current output |
| C. | high voltage and high current output |
| D. | improving the circuit efficiency |
| Answer» B. high current output | |
| 19. |
In dielectric heating, the thyristor circuits consist of |
| A. | rectifier-chopper combination |
| B. | controlled rectifier |
| C. | ac regulator |
| D. | rectifier-inverter combination |
| Answer» E. | |
| 20. |
In rectifier circuits, ripple factor RF and form factor FF are related as |
| A. | RF = (FF2 - 1)0.5 |
| B. | RF = FF |
| C. | RF = FF - 1 |
| D. | RF = (FF - 1)0.5 |
| Answer» B. RF = FF | |
| 21. |
In a fully controlled bridge converter feeding a resistive load the waveshapes of output voltage and output current |
| A. | are always similar |
| B. | can never be similar |
| C. | may be similar or dissimilar |
| D. | are similar only if a = 0 |
| Answer» B. can never be similar | |
| 22. |
A single phase cycloconverter with centre tapped input transformer requires |
| A. | 2 thyristors |
| B. | 4 thyristors |
| C. | 8 thyristors |
| D. | either 2 or 4 thyristors |
| Answer» C. 8 thyristors | |
| 23. |
A single phase full converter can operate in |
| A. | 4 quadrants |
| B. | 3 quadrants |
| C. | 2 quadrants |
| D. | 1 quadrant |
| Answer» D. 1 quadrant | |
| 24. |
In an SCR, the anode current is controlled by |
| A. | gate current only |
| B. | external circuit only |
| C. | both gate current and external circuit |
| D. | none of the above |
| Answer» C. both gate current and external circuit | |
| 25. |
A reactor is used in a dual converter operating in non-circulating current mode. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 26. |
In integral cycle control of ac regulators, the period of integral cycle control, i.e., (m + n) T should be |
| A. | less than mechanical or thermal time constant of the system |
| B. | more than the mechanical or thermal time constant of the system |
| C. | more or less than the mechanical or thermal time constant |
| D. | very high |
| Answer» B. more than the mechanical or thermal time constant of the system | |
| 27. |
Assertion (A): An inverter does not require forced commutation Reason (R): A series inverter is a forced commutation inverter. |
| 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» E. | |
| 28. |
To turn off an SCR, it is necessary to reduce its current to less than : |
| A. | trigger current |
| B. | holding current |
| C. | breakover current |
| D. | none of the above |
| Answer» C. breakover current | |
| 29. |
An ideal rectifier should have |
| A. | 100% efficiency, zero ripple factor, zero harmonic factor and unity displacement factor |
| B. | 100% efficiency, zero tipple factor, zero harmonic factor and zero displacement factor |
| C. | 100% efficiency, zero ripple factor, unity harmonic factor and unity displacement factor |
| D. | 100% efficiency, unity ripple factor, zero harmonic factor and unity displacement factor |
| Answer» B. 100% efficiency, zero tipple factor, zero harmonic factor and zero displacement factor | |
| 30. |
A class B chopper operates in third quadrant. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 31. |
Class A and class B chopper |
| 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 |
| Answer» D. may operate in either first or second quadrant | |
| 32. |
A TRIAC can be turned on : |
| A. | by applying a positive signal to gate |
| B. | by applying a negative signal to gate |
| C. | by applying either positive or negative signal to gate |
| D. | none of the above |
| Answer» D. none of the above | |
| 33. |
In a half bridge inverter each thyristor is gated at a frequency f. The output frequency is |
| A. | 2 f |
| B. | f |
| C. | 0.5 f |
| D. | 0.25 f |
| Answer» C. 0.5 f | |
| 34. |
A single phase bridge type cycloconverter uses eight thyristors. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 35. |
As compared to BJT, MOSFET has |
| A. | lower switching losses and higher conduction losses |
| B. | higher switching losses and higher conduction losses |
| C. | higher switching losses and lower conduction losses |
| D. | lower switching losses and lower conduction losses |
| Answer» B. higher switching losses and higher conduction losses | |
| 36. |
Assertion (A): Light triggering is very suitable for HVDC transmission.Reason (R): Light triggering has the advantage of complete electrical isolation of gate circuit. |
| 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 | |
| 37. |
In a single phase full converter fed by a source having inductance, the number of thyristors conducting during overlap is |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 4 |
| Answer» E. | |
| 38. |
A fully controlled bridge converter feeds a highly inductive load such that the load current can be assumed to be constant. The wave shape of input current is |
| A. | dc |
| B. | sinusoidal |
| C. | rectangular |
| D. | none of the above |
| Answer» D. none of the above | |
| 39. |
In disc mounting of SCR |
| A. | SCR is clamped on one side of disc shaped heat sink |
| B. | SCR is clamped between two disc shaped heat sinks |
| C. | The SCR has low current rating |
| D. | None of the above |
| Answer» C. The SCR has low current rating | |
| 40. |
A single phase half wave regulator uses |
| A. | 2 diodes and 2 thyristors |
| B. | 2 thyristors |
| C. | 1 diode and 1 thyristor |
| D. | 2 diodes |
| Answer» D. 2 diodes | |
| 41. |
A cycloconverter for single phase operation has |
| A. | one positive group and one negative group converters |
| B. | two positive group and two negative group converters |
| C. | three positive group and three negative group converters |
| D. | any of the above |
| Answer» B. two positive group and two negative group converters | |
| 42. |
If ton and toff are the turn on and turn off times of a thyristor, then |
| A. | ton and toff are almost equal |
| B. | ton >> toff |
| C. | toff >> ton |
| D. | ton is about twice toff |
| Answer» D. ton is about twice toff | |
| 43. |
HVDC systems are preferable for only long distances. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 44. |
A voltage VBB is applied across the terminals of a UJT. The emitter voltage at peak point is |
| A. | hVBB |
| B. | (h + 1) VBB |
| C. | hVBB + VD |
| D. | VD |
| Answer» D. VD | |
| 45. |
In a bridge inverter with single pulse width modulation |
| A. | the output frequency is equal to frequency of reference signal |
| B. | the output frequency is equal to frequency of control signal |
| C. | either (a) or (b) |
| D. | neither (a) nor (b) |
| Answer» B. the output frequency is equal to frequency of control signal | |
| 46. |
Assertion (A): Chopper always requires forced commutationReason (R): Morgan chopper uses a saturable reactor. |
| 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 | |
| 47. |
In a thyristor, the forward breakover voltage |
| A. | is constant |
| B. | may be constant or may depend on gate current |
| C. | decreases as gate current is increased |
| D. | increases as gate current is increased |
| Answer» D. increases as gate current is increased | |
| 48. |
In 180° mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 49. |
In auxiliary commutated chopper, the peak value of thyristor current is |
| A. | equal to peak value of load current |
| B. | equal to peak value of capacitor current |
| C. | sum of peak value of load current and capacitor current |
| D. | none of the above |
| Answer» D. none of the above | |
| 50. |
Assertion (A): A transistor has lower voltage drop during conduction as compared to thyristorReason (R): Transistors are manufactured in very high voltage and current ratings. |
| 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 | |