MCQOPTIONS
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MCQOPTIONS
This section includes 451 Mcqs, each offering curated multiple-choice questions to sharpen your ENGINEERING SERVICES EXAMINATION (ESE) knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Current derating may be necessary when thyristors are operating in |
| A. | series |
| B. | parallel |
| C. | series or parallel |
| D. | none of the above |
| Answer» C. series or parallel | |
| 2. |
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 | |
| 3. |
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. | 10 A |
| D. | 5 A |
| Answer» C. 10 A | |
| 4. |
The leads in a TRIAC are denoted by |
| A. | anode cathode, gate |
| B. | T1 T2, gate |
| C. | T1, T2, anode |
| D. | T1, T2, T3 |
| Answer» C. T1, T2, anode | |
| 5. |
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 | |
| 6. |
A single phase semiconverter is feeding a highly inductive load. The circuit has a freewheeling diode across the load and firing angle is α. During one cycle of input voltage, the total duration of conduction of freewheeling diode is |
| A. | α |
| B. | 2 α |
| C. | 4 α |
| D. | 0.5 α |
| Answer» C. 4 α | |
| 7. |
The number of doped regions in a SCR is |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 5 |
| Answer» D. 5 | |
| 8. |
The minimum gate current which can turn on SCR is called : |
| A. | trigger current |
| B. | holding current |
| C. | junction current |
| D. | breakover current |
| Answer» B. holding current | |
| 9. |
A cycloconverter is |
| A. | ac-dc converter |
| B. | dc-ac converter |
| C. | dc-dc converter |
| D. | ac-ac converter |
| Answer» E. | |
| 10. |
When a dc chopper feeds an RLE load, the load current, during steady state operation |
| A. | remains constant |
| B. | varies between maximum and minimum values |
| C. | may remain constant or vary |
| D. | is constant if R is constant |
| Answer» C. may remain constant or vary | |
| 11. |
In a 3 phase full wave regulator feeding a star connected resistance load the input voltage is 400 V line to line. The firing angle is 160°. The line to line output voltage would be |
| A. | 400 V |
| B. | about 100 V |
| C. | about 20 V |
| D. | zero |
| Answer» E. | |
| 12. |
Assertion (A): McMurray Bredford half bridge inverter uses complementary commutationReason (R): Three phase inverter can have two modes of operation. |
| 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 | |
| 13. |
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 | |
| 14. |
An SBS can conduct is one direction only. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 15. |
A DIAC has two terminals, anode and cathode. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 16. |
To protect an SCR against high di/dt we connect |
| A. | a capacitance in series with SCR |
| B. | a capacitance in parallel with SCR |
| C. | an inductance in parallel with SCR |
| D. | an inductance in series with SCR |
| Answer» E. | |
| 17. |
Surge current rating of an SCR is |
| A. | the maximum repetitive surge current in which the SCR can withstand |
| B. | the maximum non-repetitive surge current in which the SCR can withstand |
| C. | the maximum repetitive or non repetitive surge current in which the SCR can withstand |
| D. | the maximum surge current in which the SCR can withstand if both surge current and steady current exist together |
| Answer» C. the maximum repetitive or non repetitive surge current in which the SCR can withstand | |
| 18. |
McMurray Bedford full bridge inverter uses |
| A. | natural commutation |
| B. | auxiliary commutation |
| C. | complementary commutation |
| D. | any of the above |
| Answer» D. any of the above | |
| 19. |
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 | |
| 20. |
Which of these devices can conduct in both directions? |
| A. | SCR |
| B. | SUS |
| C. | SBS |
| D. | UJT |
| Answer» D. UJT | |
| 21. |
Assertion (A): A TRIAC is a bidirectional SCR.Reason (R): A TRIAC is a four layers 3 terminal device and 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» B. Both A and R correct but R is not correct explanation of A | |
| 22. |
Half bridge and full bridge inverters of one type use different commutation methods. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 23. |
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 | |
| 24. |
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 | |
| 25. |
The number of leads in a power semiconductor diode are |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 2 or 3 |
| Answer» B. 3 | |
| 26. |
In a controlled rectifier a freewheeling diode is necessary if the load is |
| A. | inductive |
| B. | resistive |
| C. | capacitive |
| D. | any of the above |
| Answer» B. resistive | |
| 27. |
In a single phase full wave converter (M - 2 connection), the rms transformer voltage is 300 V across each half of secondary. The PIV for each thyristor is |
| A. | 300 V |
| B. | 300/√2 V |
| C. | 600√2 V |
| D. | 300/2 V |
| Answer» D. 300/2 V | |
| 28. |
In a 3 phase full converter, the firing angle is less than 60°. The instantaneous output voltage |
| A. | will have positive part only |
| B. | will have both positive and negative parts |
| C. | may have both positive and negative parts |
| D. | will have negative part if load is inductive |
| Answer» B. will have both positive and negative parts | |
| 29. |
The two modes of operation of three phase bridge inverters are known as |
| A. | 60° mode and 120° mode |
| B. | 90° mode and 120° mode |
| C. | 120° mode and 180° mode |
| D. | 120° mode and 240° mode |
| Answer» D. 120° mode and 240° mode | |
| 30. |
A string of series connected thyristors needs equalising circuit to |
| A. | ensure proper firing |
| B. | ensure proper current division |
| C. | ensure proper voltage division |
| D. | none of the above |
| Answer» D. none of the above | |
| 31. |
The total number of leads in MOS controlled thyristor is |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 2 or 3 |
| Answer» C. 4 | |
| 32. |
Which of these commutation methods is used in AC-DC converters? |
| A. | Class A |
| B. | Class C |
| C. | Class D |
| D. | Class F |
| Answer» E. | |
| 33. |
Lead mounting for SCR is used for |
| A. | rating less than mA |
| B. | rating about 1 A or less |
| C. | rating of 20 A or less than 20 A |
| D. | rating 100 A or less |
| Answer» C. rating of 20 A or less than 20 A | |
| 34. |
In a single phase converter using a centre tapped transformer and with a highly inductive load, the firing angles is α. Each thyristor conducts for a period |
| A. | π |
| B. | α |
| C. | π - α |
| D. | π/2 |
| Answer» B. α | |
| 35. |
In a half bridge inverter the gate pulses of the two thyristors have a phase displacement of |
| A. | 60° |
| B. | 90° |
| C. | 120° |
| D. | 180° |
| Answer» E. | |
| 36. |
An RC snubber circuit is used to protect a thyristor against : |
| A. | false triggering |
| B. | failure to turn on |
| C. | switching transients |
| D. | failure to commutate |
| Answer» D. failure to commutate | |
| 37. |
The gate current required to turn on an SCR is |
| A. | few amperes |
| B. | a few mA |
| C. | almost equal to anode current |
| D. | about 50% of anode current |
| Answer» C. almost equal to anode current | |
| 38. |
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) | |
| 39. |
Assertion (A): When the anode current of an SCR starts increasing during turn on process, the anode cathode voltage drop starts decreasing. Reason (R): During turn on the reverse biased junction in SCR breaksdown. |
| 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 | |
| 40. |
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 | |
| 41. |
Assertion (A): Typical value of thermal resistance from source to sink of an SCR is about 0.3° C/WReason (R): Heat sinks of thyristors are generally made of aluminium. |
| 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 | |
| 42. |
In a dual converter both converters work as rectifiers. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 43. |
A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is Is and rms value of load current in Irms. Then |
| A. | Is = Irms irrespective of the value of firing angle |
| B. | Is = 0.5 Irms irrespective of the value of firing angle |
| C. | Is = Irms if firing angle is less than 30° |
| D. | Is = Irms if firing angle is more than 30° |
| Answer» B. Is = 0.5 Irms irrespective of the value of firing angle | |
| 44. |
A single phase electric heater uses phase controlled thyristors. The firing angle is 90°. The degree of heating is |
| A. | 25% of maximum |
| B. | 50% of maximum |
| C. | 75% of maximum |
| D. | none of the above |
| Answer» C. 75% of maximum | |
| 45. |
In a half bridge inverter, the freewheeling diodes are needed |
| A. | even when load is resistive |
| B. | only when load is inductive |
| C. | only when load is inductive or capacitive |
| D. | for all types of loads |
| Answer» D. for all types of loads | |
| 46. |
Typical values of di/dt (A/µ sec) and dv/dt (v/µ sec) 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 | |
| 47. |
In a single phase full wave regulator feeding R-L load, short gate pulse are not suitable. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 48. |
If Vdc1 is the dc output voltage in half wave controlled rectifier circuit feeding resistive load and Vdc2 is the dc output voltage in full wave controlled rectifier circuit (M - 2 connection) feeding resistive load, then |
| A. | Vdc1 = 0.5 Vdc2 for all values of firing angle |
| B. | Vdc1 = Vdc2 for all values of firing angle |
| C. | Vdc1 ≤ 0.5 Vdc2 for all values of firing angle |
| D. | Vdc1 ≥ 0.5 Vdc2 for all values of firing angle |
| Answer» B. Vdc1 = Vdc2 for all values of firing angle | |
| 49. |
In a cycloconverter it is possible to vary |
| A. | only output frequency |
| B. | only output voltage |
| C. | both output voltage and frequency but not simultaneously |
| D. | both output voltage and output frequency simultaneously |
| Answer» E. | |
| 50. |
If the frequency is less than the damped frequency in a series- inverter |
| A. | the distortion of output voltage waveform is low |
| B. | the distortion of output voltage waveform is high |
| C. | the distortion of output voltage may be high or low depending on the load impedance |
| D. | none of the above |
| Answer» C. the distortion of output voltage may be high or low depending on the load impedance | |