MCQOPTIONS
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MCQOPTIONS
This section includes 217 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering Questions knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
For commutation in three phase PAC, normally balanced three phase voltages VR, VY and VB are connected to the three legs of the converter via______________? |
| A. | Three inductances |
| B. | Three capacitances |
| C. | Three resistance |
| D. | Three transistors |
| Answer» B. Three capacitances | |
| 2. |
The typical time of rising time lies between______________? |
| A. | 10 – 20 µs |
| B. | 40 – 60 µs |
| C. | 1 – 4 µs |
| D. | 90 – 100 µs |
| Answer» D. 90 – 100 µs | |
| 3. |
Let of a thyristor Vc1, Vc2, Vc3 are forward break over voltage for gate current Ig1, Ig2, Ig3 respectively. Then________________? |
| A. | Vc1 > Vc2 > Vc3 when Ig1 > Ig2 > Ig3. |
| B. | Vc1 > Vc2 > Vc3 when Ig1 < Ig2 < Ig3. |
| C. | Vc1 = Vc2 = Vc3 any value of Ig. |
| D. | Vc1 > Vc2 > Vc3 when Ig1 ≥ Ig2 &Atil |
| Answer» C. Vc1 = Vc2 = Vc3 any value of Ig. | |
| 4. |
When a large surge current of very short duration flows through a thyristor then which one of the following device will operate to protect the thyristor ___________? |
| A. | CB |
| B. | Snubber circuit |
| C. | Voltage clamping device |
| D. | Fast acting current limiting device (FACL fuse) |
| Answer» E. | |
| 5. |
Which of following is normally ON device? |
| A. | SIT |
| B. | BJT |
| C. | TRIAC |
| D. | IGBT |
| Answer» B. BJT | |
| 6. |
Maximum di / dt in a SCR is________? |
| A. | Directly proportional to Vm of supply voltage |
| B. | Inversely proportional to Vm of supply voltage |
| C. | Inversely proportional to L in the circuit |
| D. | Both A and C |
| Answer» B. Inversely proportional to Vm of supply voltage | |
| 7. |
During gate recovery time_____________? |
| A. | charge carriers of J2 junction recombined |
| B. | charge carriers of J2 junction is swept out |
| C. | charge carrier of J1 junction removed |
| D. | charge carriers of J3 junction is removed |
| Answer» B. charge carriers of J2 junction is swept out | |
| 8. |
To meet high current demand we use SCRs in______________? |
| A. | series connection |
| B. | parallel connection |
| C. | anti parallel connection |
| D. | both B and C. |
| Answer» C. anti parallel connection | |
| 9. |
In reverse blocking mode of a thyristor______? |
| A. | junction J2 is in reverse bias and J1, J3 is in forward bias |
| B. | junction J3 is in forward bias and J1, J2 in reverse bias |
| C. | junction J1, J3 is in reverse bias and J2 is in forward bias |
| D. | junction J1 and J2 is in forward bias and J3 is in reverse bias |
| Answer» D. junction J1 and J2 is in forward bias and J3 is in reverse bias | |
| 10. |
If a shunt motor is started with its field winding open then___________? |
| A. | It will rotate at the same speed as that with its field winding closed |
| B. | It will rotate at less speed as that with its field winding closed |
| C. | It will rotate at dangerously high speed |
| D. | None of these |
| Answer» D. None of these | |
| 11. |
If energy is taken from the AC side of the inverter and sends it back into the DC side, then it is known as___________? |
| A. | Motoring mode operation |
| B. | Braking mode operation |
| C. | Regenerative mode operation |
| D. | None of these |
| Answer» D. None of these | |
| 12. |
TRIAC is a semiconductor power electronic device which contains____________? |
| A. | Two SCR’s connected in reverse parallel |
| B. | Two SCR’s connected in parallel |
| C. | Two SCR’s connected in series |
| D. | Two BJT’s connected in series |
| Answer» B. Two SCR’s connected in parallel | |
| 13. |
For similar carrier and modulating signals, the line current used in CSI is_____________? |
| A. | Identical to line voltage in a VSI |
| B. | Identical to line current in VSI |
| C. | Identical to phase voltage in VSI |
| D. | Identical to phase voltage in CSI |
| Answer» B. Identical to line current in VSI | |
| 14. |
During the commutation period in 3 phase converter, overlap time is____________? |
| A. | Dependent on the load current |
| B. | Dependent on the voltage |
| C. | Dependent on both the load current and load voltage behind the short circuit current |
| D. | Independent on both the load current and load voltage |
| Answer» D. Independent on both the load current and load voltage | |
| 15. |
A combination of synchronized leading edge and trailing edge modulation has also been used to control a____________? |
| A. | Boost single – phase power factor converter |
| B. | A buck dc – dc converter to reduce ripple in the intermediate dc bus capacitor |
| C. | Both A. and B. |
| D. | None f these |
| Answer» D. None f these | |
| 16. |
In a push – pull converter, the filter capacitor can be obtained as____________? |
| A. | Cmin = V / ( Vr L f2 ) |
| B. | Cmin= ( 1 – D ) V / ( Vr L f2 ) |
| C. | Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 ) |
| D. | Cmin= ( 1 – 2 D ) V / 42 ( Vr L f2 ) |
| Answer» D. Cmin= ( 1 – 2 D ) V / 42 ( Vr L f2 ) | |
| 17. |
The effects of EMI can be reduced by_____________? |
| A. | Suppressing emissions |
| B. | Reducing the efficiency of the coupling path |
| C. | Reducing the susceptibility of the receptor |
| D. | All of these |
| Answer» E. | |
| 18. |
In a flyback converter, the inductor of the buck-boost converter has been replaced by a_____________? |
| A. | Flyback capacitor |
| B. | Flyback resistor |
| C. | Flyback transformer |
| D. | Flyback transistor |
| Answer» D. Flyback transistor | |
| 19. |
MOSFET stands for______________? |
| A. | Metal – oxide semiconductor field effect transistor |
| B. | Molybdenum – oxide semiconductor field effect transistor |
| C. | Metal – oxide silicon field effect transistor |
| D. | Metal – oxide semiconductor field effect transmitter |
| Answer» B. Molybdenum – oxide semiconductor field effect transistor | |
| 20. |
Advantages of Cuk converter is / are_____________? |
| A. | Large number of reactive component |
| B. | Low stress on switch |
| C. | Low stress on capacitor |
| D. | None of these |
| Answer» E. | |
| 21. |
A MOSFET, for its conduction uses_____________? |
| A. | Only minority carriers |
| B. | Only majority carriers |
| C. | Both minority and majority carriers |
| D. | None of these |
| Answer» C. Both minority and majority carriers | |
| 22. |
An RC snubber network used in BJT__________? |
| A. | Divert the collector current during turn – off |
| B. | Improves the reverse bias safe operating area |
| C. | Dissipates a fair amount of switching power |
| D. | All of these |
| Answer» E. | |
| 23. |
The ac output voltage waveform of VSI and AC output current waveform of CSI respectively is composed of___________? |
| A. | High dv / dt, low di / dt |
| B. | Low dv / dt, low di / dt |
| C. | Low dv / dt, high di / dt |
| D. | High dv / dt, high di / dt |
| Answer» E. | |
| 24. |
An SCR is made up of silicon because_____________? |
| A. | silicon has large leakage current than germanium |
| B. | silicon has small leakage current than germanium |
| C. | silicon has small leakage voltage than germanium |
| D. | silicon has large leakage voltage than germanium |
| Answer» C. silicon has small leakage voltage than germanium | |
| 25. |
In forward blocking mode of a thyristor________? |
| A. | junction J2 is in reverse bias and J1, J3 is in forward bias |
| B. | junction J3 is in forward bias and J1, J2 is in reverse bias |
| C. | Junction J1, J3 is in reverse bias and J2 is in forward bias |
| D. | Junction J1 and J2 is in forward bias and J3 is in reverse bias |
| Answer» B. junction J3 is in forward bias and J1, J2 is in reverse bias | |
| 26. |
AC power in a load can be controlled by using_____________? |
| A. | two SCR’s in parallel opposition |
| B. | two SCR’s in series |
| C. | three SCR’s in series |
| D. | four SCR’s in series |
| Answer» B. two SCR’s in series | |
| 27. |
Regulator sampling PWM is usually used in___________? |
| A. | High power inverters |
| B. | Rectifiers |
| C. | Low power inverters |
| D. | Only A. and B. |
| Answer» E. | |
| 28. |
A thyristor can termed as__________? |
| A. | AC switch |
| B. | DC switch |
| C. | Both a and B |
| D. | Square wave switch |
| Answer» C. Both a and B | |
| 29. |
Electrical power output in a D.C. generator is equal to_____________? |
| A. | Electrical power developed in armature – copper losses |
| B. | Mechanical power input – iron and friction losses |
| C. | Electrical power developed in armature – iron and copper losses |
| D. | Mechanical power input – iron and friction losses – copper losses |
| Answer» E. | |
| 30. |
The switching function of semiconductor devices can be characterized with____________? |
| A. | Duty ratio only |
| B. | Frequency only |
| C. | Duty ratio and frequency |
| D. | Duty ratio, frequency and time delay |
| Answer» E. | |
| 31. |
The power demand can be estimated approximately by____________? |
| A. | Load survey method |
| B. | Mathematical method |
| C. | Statistical method |
| D. | Economic parameters |
| Answer» D. Economic parameters | |
| 32. |
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. | |
| 33. |
An SCR has half cycle surge current rating of 3000 A for 50 Hz supply. One cycle surge current will be_____? |
| A. | 1500 A |
| B. | 6000 A |
| C. | 2121.32 A. |
| D. | 4242.64 A. |
| Answer» D. 4242.64 A. | |
| 34. |
The typical value of SCR for modern alternator is____________? |
| A. | 1.5 |
| B. | 0.5 |
| C. | 1.0 |
| D. | 1.2 |
| Answer» C. 1.0 | |
| 35. |
How can we protect SCR from thermal conditions _____________? |
| A. | Use of snubber circuit |
| B. | Using heat sink |
| C. | Using CB and fuse |
| D. | Using equalizing circuit |
| Answer» C. Using CB and fuse | |
| 36. |
Which of the following is used in heat sink_____________? |
| A. | Iron |
| B. | Aluminium |
| C. | Carbon |
| D. | Silver |
| Answer» C. Carbon | |
| 37. |
A carrier based PWM technique in CSI is composed of____________? |
| A. | A switching pulse generator and a shorting pulse generator |
| B. | A shorting pulse distributor |
| C. | A switching and shorting pulse combination |
| D. | All of these |
| Answer» E. | |
| 38. |
If holding current of a thyristor is 2 mA then latching current should be_____? |
| A. | 0.01 A. |
| B. | 0.002 A. |
| C. | 0.009 A. |
| D. | 0.004 A. |
| Answer» E. | |
| 39. |
Gate circuit or triggering circuit of a thyristor is |
| A. | lower power circuit |
| B. | high power circuit |
| C. | magnetic circuit |
| D. | may be low power or high power circuit |
| Answer» B. high power circuit | |
| 40. |
Thyristor is nothing but a____________? |
| A. | Controlled transistor |
| B. | Controlled switch |
| C. | Amplifier with higher gain |
| D. | Amplifier with large current gain |
| Answer» C. Amplifier with higher gain | |
| 41. |
After proper turn on of thyristor____________? |
| A. | gate signal is always present |
| B. | gate signal must be removed |
| C. | gate signal should present but can be removed |
| D. | none of the above |
| Answer» C. gate signal should present but can be removed | |
| 42. |
SCR will be turned off when anode current is_______________? |
| A. | < latching current but greater than holding current and gate signal is 0. |
| B. | less than holding current |
| C. | < latching current but greater than holding current and gate signal is present. |
| D. | both (A) and (B). |
| Answer» E. | |
| 43. |
The capacitance of reversed bised junction J2 in a thyristor is CJ2 = 20 pF and can be assumed to be independant of the off state voltage. The limiting value of the charging current to turn on the thyristor is 16 mA. What is the critical value of dv/dt? |
| A. | 600 V/µs |
| B. | 800 V/µs |
| C. | 1200 V/µs |
| D. | 1000 V/µs |
| Answer» C. 1200 V/µs | |
| 44. |
BCT is used for____________? |
| A. | High power phase control |
| B. | High power current control |
| C. | Low power current control |
| D. | Low power phase control |
| Answer» B. High power current control | |
| 45. |
For an SCR gate – cathode characteristic is a straight line of 130. For triggered source volume of 15 V and allowable gate power dissipation of 0.5 W compute the gate source resistance_____? |
| A. | 111.9 Ω. |
| B. | 11.19 Ω. |
| C. | 108 Ω. |
| D. | 115 Ω |
| Answer» B. 11.19 Ω. | |
| 46. |
The function of snubber circuit connected across the SCR is to___________? |
| A. | Suppress dV / dt. |
| B. | Increase dV / dt. |
| C. | Decrease dV / dt. |
| D. | Decrease di / dt. |
| Answer» B. Increase dV / dt. | |
| 47. |
A step up chopper has input voltage 110 V and output voltage 150 V. The value of duty cycle is_____? |
| A. | 0.32 |
| B. | 0.67 |
| C. | 0.45 |
| D. | 0.27 |
| Answer» E. | |
| 48. |
Which statement is true for latching current ___________? |
| A. | It is related to turn off process of the device |
| B. | It is related to conduction process of device |
| C. | It is related to turn on process of the device |
| D. | Both C and D. |
| Answer» D. Both C and D. | |
| 49. |
Silicon controlled rectifier can be turned on____________? |
| A. | By applying a gate pulse and turned off only when current becomes zero |
| B. | And turned off by applying gate pulse |
| C. | By applying a gate pulse and turned off by removing the gate pulse |
| D. | By making current non zero and turned off by making current zero |
| Answer» B. And turned off by applying gate pulse | |
| 50. |
Form factor of a rectifier is the ratio of ______________? |
| A. | Root mean square value of voltage and current to its peak value |
| B. | Root mean square value of voltage and current to its average value |
| C. | Average value of current and voltage to its root mean square value |
| D. | Peak value of current and voltage to its root mean square value |
| Answer» C. Average value of current and voltage to its root mean square value | |