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. |
The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by |
| A. | forward characteristics of thyristors |
| B. | reverse recovery characteristics of thyristors |
| C. | both forward and reverse recovery characteristics of thyristors |
| D. | none of the above |
| Answer» C. both forward and reverse recovery characteristics of thyristors | |
| 2. |
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 | |
| 3. |
In controlled heating circuits, thyristors act as |
| A. | rectifier |
| B. | inverter |
| C. | ac regulator |
| D. | chopper |
| Answer» D. chopper | |
| 4. |
Which of these commutation methods uses two leads? |
| A. | Class A |
| B. | Class B |
| C. | Class C |
| D. | Class D |
| Answer» E. | |
| 5. |
A single phase fully controlled bridge converter is fed by a voltage Vm sin ωt. The average and rms values of output voltage are |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 6. |
The condition for underdamped oscillations in a series RLC circuit is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 7. |
The circuit in figure is for |
| A. | resonant commutation |
| B. | self commutation |
| C. | load commutation |
| D. | auxiliary commutation |
| Answer» C. load commutation | |
| 8. |
The turn on characteristics of a power transistor can be assumed to be linear, as shown in the below figure . During turn on time T, voltage reduces linearly from V to 0 and current rises linearly from 0 to I. The energy loss during time T is |
| A. | VIT |
| B. | VIT/2 |
| C. | VIT/3 |
| D. | VIT/6 |
| Answer» E. | |
| 9. |
A single phase half wave converter is feeding-a resistor load. The input voltage is v = Vm sin ωt. If firing angle is zero, the output dc voltage Vdc and output rms voltage Vrms respectively |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 10. |
A capacitor C farads is charged to a voltage V. It discharges through a thyristor, a diode and an inductance L. The peak current in the circuit is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 11. |
In auxiliary commutated chopper fed by voltage V and having L and C commutating elements, the peak value of capacitor current is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 12. |
Two single phase semi-converters are connected in series to form a series converter. The input is v = Vm sin ωt and α1, α2 are the firing angles. If α1 = 0, the dc output voltage is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 13. |
In a full bridge inverter fed by a battery of voltage V, the rms value of fundamental component of output voltage is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 14. |
A single phase converter is fed by a source having an inductance L. If load current is I₀, the decrease in output voltage due to overlap is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 15. |
A dc chopper feeds an RLE load and has a duty cycle of 1. The load current will be such that |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 16. |
In figure, thyristor Th is in off state. When thyristor is turned on, the peak thyristor current can be |
| A. | 5 A |
| B. | 10 A |
| C. | 15 A |
| D. | 20 A |
| Answer» D. 20 A | |
| 17. |
In a step down chopper using time ratio control, the input voltage is V and duty cycle is α. The load is purely resistive having resistance R. The average and rms load currents are |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 18. |
If a step down chopper is fed by a dc voltage V with Ton and Toff are on and off periods then following is |
| A. | average output voltage |
| B. | rms output voltage |
| C. | average or rms output voltage depending on load |
| D. | neither of the above |
| Answer» B. rms output voltage | |
| 19. |
In the circuit of figure, the waveshape of load current when thyristor conducting is |
| A. | constant |
| B. | increasing exponentially |
| C. | decreasing exponentially |
| D. | either (b) or (c) |
| Answer» C. decreasing exponentially | |
| 20. |
If 0.5 T is the time period of oscillations and Toff is the time between turn off of one thyristor and turn on of second thyristor, the frequency of output f of a series inverter is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 21. |
In a semi converter feeding a resistive load, the firing angle is α. Each thyristor conducts for |
| A. | π radians |
| B. | (π - α) radians |
| C. | (π + α) radians |
| D. | (π - 0.5 α) radians |
| Answer» C. (π + α) radians | |
| 22. |
A fully controlled bridge converter can operate in quadrants |
| A. | 1 |
| B. | 1 and 2 |
| C. | 1 and 3 |
| D. | 1 and 4 |
| Answer» E. | |
| 23. |
A 750 A circuit uses thyristor of current rating 175 A. If derating is 25%, the number of thyristors in parallel is |
| A. | 3 |
| B. | 4 |
| C. | 6 |
| D. | 10 |
| Answer» D. 10 | |
| 24. |
A single phase semiconverter is feeding a highly inductive load and has a freewheeling diode across the load. The waveshape of input current is |
| A. | sinusoidal |
| B. | rectangular |
| C. | sinusoidal or rectangular |
| D. | triangular |
| Answer» C. sinusoidal or rectangular | |
| 25. |
From which instant is the turn off time of a thyristor defined |
| 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 |
| Answer» C. when both anode voltage and current become zero | |
| 26. |
The cut in voltages for germanium and silicon diodes respectively as |
| A. | 0.3 V and 0.7 V |
| B. | 0.7 V and 0.3 V |
| C. | 0.6 V and 0.9 V |
| D. | 0.5 V and 0.7 V |
| Answer» B. 0.7 V and 0.3 V | |
| 27. |
A thyristor has maximum allowable junction temperature of 110° C and the ambient temperature is 40°C, If the maximum internal power dissipation is 50 W, the thermal resistance is |
| A. | 2° C/W |
| B. | 1.4° C/W |
| C. | 0.7°C/W |
| D. | 2.2° C/W |
| Answer» C. 0.7°C/W | |
| 28. |
The load circuit of a single phase full bridge inverter |
| A. | must be underdamped |
| B. | must be overdamped |
| C. | may be underdamped or overdamped |
| D. | may be any type of load |
| Answer» E. | |
| 29. |
In the below figure, the load is highly inductive. The firing angle is a for each of the thyristors. The periods of conduction of Th1 and Th2 respectively are |
| A. | 0 to π and π to 2π |
| B. | α to π and π + a to 2π |
| C. | α to π + α and π + π to 2π + α |
| D. | α to π - α and π + α to 2π - α |
| Answer» D. α to π - α and π + α to 2π - α | |
| 30. |
A semi converter operates in two quadrants. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 31. |
A 3 phase ac regulator uses |
| A. | 3 thyristors |
| B. | 6 thyristors |
| C. | 9 thyristors |
| D. | 12 thyristors |
| Answer» C. 9 thyristors | |
| 32. |
A semiconverter feeding an RLE load operates in |
| A. | first quadrant only |
| B. | first and second quadrants |
| C. | first and fourth quadrants |
| D. | first and third quadrants |
| Answer» B. first and second quadrants | |
| 33. |
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. |
| 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. | |
| 34. |
In a single phase full wave ac regulator the rms value of load current is 20 A load is purely resistive. Then |
| A. | average thyristor current will be less than 20 A but rms thyristor current will be more than 20 A |
| B. | both the average and rms thyristor currents will be less than 20 A |
| C. | both the average and rms thyristor currents will be more than 20 A |
| D. | rms thyristor current will be 20 A and average thyristor current will be 10 A |
| Answer» C. both the average and rms thyristor currents will be more than 20 A | |
| 35. |
A current source inverter has simple commutation circuit. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 36. |
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 | |
| 37. |
In a 3 phase bridge inverter with 120° mode of operation the. number of thyristors conducting at one time are |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 4 |
| Answer» C. 3 | |
| 38. |
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. | |
| 39. |
Which chopper circuit operates in quadrants 1 and 4? |
| A. | A |
| B. | B |
| C. | D |
| D. | E |
| Answer» D. E | |
| 40. |
A single phase half wave controlled rectifier circuit has an R-L load. A freewheeling diode is also in the circuit. When freewheeling diode is conducting the SCR |
| A. | is forward biased |
| B. | is reverse biased |
| C. | may be forward biased or reverse biased |
| D. | forward biased initially but reverse biased afterwards |
| Answer» C. may be forward biased or reverse biased | |
| 41. |
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 | |
| 42. |
In a single phase full wave converter (M-2 connection) feeding on R-L load the input voltage is v = Vm sin ωt. The expression for rms output voltage is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 43. |
A 3 kV circuit uses SCR of 800 V rating. If derating is 25%, the number of SCRs in series is |
| A. | 4 |
| B. | 5 |
| C. | 6 |
| D. | 8 |
| Answer» C. 6 | |
| 44. |
Assertion (A): A DIAC has four layers but only two terminals. Reason (R): A DIAC can conduct in both directions. |
| 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 | |
| 45. |
HVDC systems are preferable for only long distances. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 46. |
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 | |
| 47. |
The output wave of a cycloconverter consists of a number of segments derived from the input wave. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 48. |
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 | |
| 49. |
The total number of leads in SUS, SBS and SCS respectively are |
| A. | 3, 3, 4, |
| B. | 3, 3, 3 |
| C. | 2, 3, 3 |
| D. | 3, 3, 5 |
| Answer» B. 3, 3, 3 | |
| 50. |
Which of these triggering methods for series connected SCRs use LASCR in the gate circuit? |
| A. | Resistance triggering |
| B. | Simultaneous triggering |
| C. | Sequential triggering |
| D. | Optical triggering |
| Answer» E. | |