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 control method used for PWM dc - dc converter is |
| A. | Voltage mode control |
| B. | Current mode control |
| C. | Hysteric control |
| D. | All of these |
| Answer» C. Hysteric control | |
| 2. |
A triac is equivalent to two SCRs ___________. |
| A. | In parallel |
| B. | In series |
| C. | In inverse-parallel |
| D. | None of the above |
| Answer» D. None of the above | |
| 3. |
The triac is ___________. |
| A. | Like a bidirectional SCR |
| B. | A four-terminal device |
| C. | Not a thyristor |
| D. | None of the above |
| Answer» B. A four-terminal device | |
| 4. |
When a UJT is turned ON, the resistance between emitter terminal and lower base terminal ___________ |
| A. | Remains the same |
| B. | Is decreased |
| C. | Is increased |
| D. | None of the above |
| Answer» C. Is increased | |
| 5. |
A diac has ___________ semiconductor layers |
| A. | Three |
| B. | Two |
| C. | Four |
| D. | None of the above |
| Answer» B. Two | |
| 6. |
A triac has ___________ semiconductor layers. |
| A. | Two |
| B. | Three |
| C. | Four |
| D. | Five |
| Answer» D. Five | |
| 7. |
A diac is simply ___________. |
| A. | A single junction device |
| B. | A three junction device |
| C. | A triac without gate terminal |
| D. | None of the above |
| Answer» D. None of the above | |
| 8. |
A diac is ___________ switch |
| A. | An c. |
| B. | A d.c. |
| C. | A mechanical |
| D. | None of the above |
| Answer» B. A d.c. | |
| 9. |
Power electronics essentially deals with control of a.c. power at ___________. |
| A. | Frequencies above 20 kHz |
| B. | Frequencies above 1000 kHz |
| C. | Frequencies less than 10 Hz |
| D. | 50 Hz frequency |
| Answer» E. | |
| 10. |
When the temperature increases, the inter-base resistance (RBB) of a UJT ___________. |
| A. | Increases |
| B. | Decreases |
| C. | Remains the same |
| D. | None of the above |
| Answer» B. Decreases | |
| 11. |
A Triac has three terminals viz ___________ |
| A. | Drain, source, gate |
| B. | Two main terminal and a gate terminal |
| C. | Cathode, anode, gate |
| D. | None of the above |
| Answer» C. Cathode, anode, gate | |
| 12. |
The V-I characteristics for a triac in the first and third quadrants are essentially identical to those of ___________ in its first quadrant |
| A. | Transistor |
| B. | SCR |
| C. | UJT |
| D. | none of the above |
| Answer» C. UJT | |
| 13. |
The device that does not have the gate terminal is ___________. |
| A. | Triac |
| B. | FET |
| C. | SCR |
| D. | Diac |
| Answer» E. | |
| 14. |
In a UJT, the p-type emitter is ___________ doped |
| A. | Lightly |
| B. | Heavily |
| C. | Moderately |
| D. | None of the above |
| Answer» C. Moderately | |
| 15. |
When the temperature increases, the intrinsic stand off ratio ___________. |
| A. | Increases |
| B. | Decreases |
| C. | Essentially remains the same |
| D. | None of the above |
| Answer» D. None of the above | |
| 16. |
When the emitter terminal of a UJT is open, the resistance between the base terminal is generally ___________. |
| A. | High |
| B. | Low |
| C. | Extremely low |
| D. | None of the above |
| Answer» B. Low | |
| 17. |
The device that exhibits negative resistance region is ___________. |
| A. | Diac |
| B. | Triac |
| C. | Transistor |
| D. | UJT |
| Answer» E. | |
| 18. |
A diac is turned on by ___________. |
| A. | A breakover voltage |
| B. | Gate voltage |
| C. | Gate current |
| D. | None of the above |
| Answer» B. Gate voltage | |
| 19. |
A UJT is sometimes called ___________ diode. |
| A. | Low resistance |
| B. | High resistance |
| C. | Single-base |
| D. | Double-base |
| Answer» E. | |
| 20. |
To turn on UJT, the forward bias on the emitter diode should be ___________ the peak point voltage. |
| A. | Less than |
| B. | Equal to |
| C. | More than |
| D. | None of the above |
| Answer» D. None of the above | |
| 21. |
After peak point, the UJT operates in the ___________ region. |
| A. | Cut-off |
| B. | Saturation |
| C. | Negative resistance |
| D. | None of the above |
| Answer» D. None of the above | |
| 22. |
Between the peak point and the valley point of UJT emitter characteristics we have ___________ region |
| A. | Saturation |
| B. | Negative resistance |
| C. | Cut-off |
| D. | None of the above |
| Answer» C. Cut-off | |
| 23. |
A triac can pass a portion of ___________ half-cycle through the load. |
| A. | Only positive |
| B. | Only negative |
| C. | Both positive and negative |
| D. | None of the above |
| Answer» D. None of the above | |
| 24. |
Which of the following is not a characteristic of UJT? |
| A. | Intrinsic stand off ratio |
| B. | Negative resistance |
| C. | Peak-point voltage |
| D. | Bilateral conduction |
| Answer» E. | |
| 25. |
The normal way to turn on a diac is by ___________. |
| A. | Gate current |
| B. | Gate voltage |
| C. | Breakover voltage |
| D. | None of the above |
| Answer» D. None of the above | |
| 26. |
A triac is a ___________ switch |
| A. | Bidirectional |
| B. | Unidirectional |
| C. | Mechanical |
| D. | None of the above |
| Answer» B. Unidirectional | |
| 27. |
A diac has ___________ terminals. |
| A. | Two |
| B. | Three |
| C. | Four |
| D. | None of the above |
| Answer» B. Three | |
| 28. |
A diac has ___________ pn junctions |
| A. | Four |
| B. | Two |
| C. | Three |
| D. | None of the above |
| Answer» C. Three | |
| 29. |
The UJT may be used as ___________. |
| A. | Am amplifier |
| B. | A sawtooth generator |
| C. | A rectifier |
| D. | None of the above |
| Answer» C. A rectifier | |
| 30. |
A UJT has ___________. |
| A. | Two pn junctions |
| B. | One pn junction |
| C. | Three pn junctions |
| D. | None of the above |
| Answer» C. Three pn junctions | |
| 31. |
A single phase cycloconverter feeds a resistance heating load. The heating power is provided by |
| A. | only the fundamental component of output wave |
| B. | only higher harmonics in the output wave |
| C. | both fundamental and higher harmonics in the output wave |
| D. | either (a) or (b) |
| Answer» D. either (a) or (b) | |
| 32. |
The static equalisation circuit for thyristors connected in series is |
| A. | one resistor in series with each thyristor |
| B. | one resistor in parallel with each thyristor |
| C. | one resistor and one capacitor in parallel with each thyristor |
| D. | none of the above |
| Answer» C. one resistor and one capacitor in parallel with each thyristor | |
| 33. |
When a single phase dual converter is operating in circulating current mode |
| A. | both converters are working as rectifiers simultaneously |
| B. | one converter is always working as rectifier and the other as inverter |
| C. | only one converter is working at one time |
| D. | both converters are either working as rectifiers or as inverters simultaneously |
| Answer» C. only one converter is working at one time | |
| 34. |
The efficiency of a chopper circuit is about |
| A. | around 20% |
| B. | around 5% |
| Answer» B. around 5% | |
| 35. |
Thyristors can be used for control of |
| A. | dc separately excited motor |
| B. | dc shunt motor |
| C. | dc series motor |
| D. | all of the above |
| Answer» E. | |
| 36. |
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. | |
| 37. |
A single phase full converter gives maximum and minimum output voltage at firing angles of |
| A. | 0 and 180° respectively |
| B. | 180° and 0° respectively |
| C. | 0 and 90° respectively |
| D. | 90° and 0° respectively |
| Answer» B. 180¬∞ and 0¬∞ respectively | |
| 38. |
Assertion (A): A fully controlled bridge converter can operate in first and fourth quadrant.Reason (R): A semi converter is cheaper than a full converter. |
| 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 | |
| 39. |
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. | |
| 40. |
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 | |
| 41. |
The number of layers in a Shockley diode are |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 2 or 3 |
| Answer» D. 2 or 3 | |
| 42. |
In a single phase semiconverter feeding a highly inductive load, the load current is |
| A. | sinusoidal |
| B. | nearly constant |
| C. | absolutely constant |
| D. | rectangular |
| Answer» C. absolutely constant | |
| 43. |
Assertion (A): The gate current of an SCR is always in the form of pulses. Reason (R): The gate losses, in pulse triggering, are low. |
| 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 | |
| 44. |
Two single phase semi-converters are connected in series to form a series converter. The input is v = Vm sin ωt and a1, a2 are the firing angles. If a1 = 0, the dc output voltage is |
| A. | (1 + cos a2) |
| B. | (2 + cos a2) |
| C. | (3 + cos a2) |
| D. | (4 + cos a2) |
| Answer» D. (4 + cos a2) | |
| 45. |
A single phase fully controlled bridge rectifier is fed by a source having inductance. The output voltage during overlap period is |
| A. | Vm |
| B. | 0.5 Vm |
| C. | zero |
| D. | 0.5 Vm - voltage drop across inductance |
| Answer» D. 0.5 Vm - voltage drop across inductance | |
| 46. |
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 | |
| 47. |
Which chopper circuit uses saturable reactor? |
| A. | Auxiliary commutated |
| B. | Jones chopper |
| C. | Morgan chopper |
| D. | Load commutated |
| Answer» D. Load commutated | |
| 48. |
A relaxation oscillator uses |
| A. | tunnel diode |
| B. | UJT |
| C. | both tunnel diode and UJT |
| D. | PIN diode |
| Answer» C. both tunnel diode and UJT | |
| 49. |
A 3 phase semiconverter when supplying a certain load has a rectification efficiency of 0.6 and transformer utilisation factor of 0.35. When a 3 phase full converter is supplying the same load |
| A. | rectification efficiency will be more than 0.6 and TUF will be more than 0.35 |
| B. | rectification efficiency will be more than 0.6 but TUF will be less than 0.35 |
| C. | rectification efficiency will be less than 0.6 and TUF will be less than 0.35 |
| D. | rectification efficiency will be less than 0.6 but TUF will be more than 0.35 |
| Answer» B. rectification efficiency will be more than 0.6 but TUF will be less than 0.35 | |
| 50. |
The method of triggering SCS is |
| A. | application of pulse at cathode gate |
| B. | application of low voltage at anode |
| Answer» B. application of low voltage at anode | |