MCQOPTIONS
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MCQOPTIONS
This section includes 554 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
For 3 phase rotary converters, when power factor is unity. the ac line to dccurrent ratio is |
| A. | 1.5 |
| B. | 1.1 |
| C. | 1.0 |
| D. | 0.942. |
| Answer» E. | |
| 2. |
When a thyristor turn on, the gate drive: |
| A. | can be turned down but thyristor remains in on position |
| B. | cannot be turned down as thyristor will be turned off |
| C. | gate drive has no impact on starting and turning off the thyristor |
| D. | none of the above |
| Answer» B. cannot be turned down as thyristor will be turned off | |
| 3. |
In a three phase half-wave cycloconverter ___________ |
| A. | both inverting and converting action takes place |
| B. | only inversion action takes place |
| C. | only converting action takes place |
| D. | none of the mentioned |
| Answer» B. only inversion action takes place | |
| 4. |
The frequency of the ripple in the output voltage of 3-phase semiconductor depends on: |
| A. | Firing angle and load resistance |
| B. | Firing angle and load inductance |
| C. | The load circuit parameters |
| D. | Firing angle and the supply frequency |
| Answer» E. | |
| 5. |
Current derating may be necessary when thyristors areoperating in |
| A. | Series |
| B. | Parallel |
| C. | series or parallel |
| D. | none of the above |
| Answer» C. series or parallel | |
| 6. |
In a single phase half-wave thyristor circuit with R load & Vs=Vm sinωt,the maximum value of the load current can be given by |
| A. | 2Vm/R |
| B. | Vs/R |
| C. | Vm/2 |
| D. | Vs/2 |
| Answer» D. Vs/2 | |
| 7. |
Least undulating current will be delivered by which mercury arc rectifier |
| A. | 1-phase |
| B. | 2 phase |
| C. | 3 phase |
| D. | 6 phase. |
| Answer» E. | |
| 8. |
Harmonics in 3 phase inverters can be reduced by using |
| A. | Passive filter |
| B. | Active filter |
| C. | Both passive and active filters |
| D. | None of these |
| Answer» D. None of these | |
| 9. |
In the method of phase control, the phase relationship between ___ & ___ iscontrolled by varying the firing angle |
| A. | supply current, supply voltage |
| B. | end of the load current, end of the load voltage |
| C. | start of the load current, start of the load voltage |
| D. | load current, load voltage |
| Answer» D. load current, load voltage | |
| 10. |
Calculate the output voltage of the Boost converter if the supply voltage is156 V and duty cycle value is .4. |
| A. | 260 V |
| B. | 264 V |
| C. | 261 V |
| D. | 268 V |
| Answer» B. 264 V | |
| 11. |
On load tap changer using thyristors can have a maximum of twotaps. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» C. none | |
| 12. |
Buck-Boost acts as Boost converter for duty cycle is equal to _________ |
| A. | .8 |
| B. | .1 |
| C. | .2 |
| D. | .4 |
| Answer» B. .1 | |
| 13. |
In a thyristor, ratio of latching current to holding current is: |
| A. | 0.4 |
| B. | 1.0 |
| C. | 2.5 |
| D. | 4.0 |
| Answer» D. 4.0 | |
| 14. |
The vacuum inside the glass bulb of a mercury arc rectifier is of the order of |
| A. | 5 x 10-3 cm of Hg |
| B. | 5 x 10-4 cm of Hg |
| C. | 5 x 10-5 cm of Hg |
| D. | 5 x 10-8 cm of Hg. |
| Answer» D. 5 x 10-8 cm of Hg. | |
| 15. |
What is the formula for output voltage for Buck converter? |
| A. | 8D×Vin |
| B. | 5D×Vin |
| C. | 2D×Vin |
| D. | D×Vin |
| Answer» E. | |
| 16. |
On state voltage drop across thyristor used in a 230 V supplysystem is of the order: |
| A. | 110-115V |
| B. | 250 V |
| C. | 1- 1.5 V |
| D. | none of the above |
| Answer» D. none of the above | |
| 17. |
In sinusoidal PWM for inverters the width of different pulses are notthe same. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 18. |
In a 3 phase bridge rectifier the ripple frequency is |
| A. | Equal to the input frequency |
| B. | Twice the input frequency |
| C. | Three times the input frequency |
| D. | Six times the input frequency |
| Answer» E. | |
| 19. |
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. | |
| 20. |
In GTO The anode current is ideally limited by the |
| A. | gate pulse amplitude |
| B. | internal impedance of the device |
| C. | load Impedance |
| D. | gate circuit impedance |
| Answer» D. gate circuit impedance | |
| 21. |
An IGBT has three terminals called: |
| A. | Collector, Emitter and Base |
| B. | Drain, Source and Base |
| C. | Drain, Source and Gate |
| D. | Collector, Emitter and Gate |
| Answer» E. | |
| 22. |
Choppers are used to control the DC voltage level. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 23. |
During forward blocking state, a thyristor is associated with: |
| A. | large current and low voltage |
| B. | low current and large voltage |
| C. | medium current and large voltage |
| D. | None of the above |
| Answer» C. medium current and large voltage | |
| 24. |
In current commutated DC-DC choppers, the voltage spike appears acrossthe load when |
| A. | Voltage across the commutating inductances collapses |
| B. | The capacitance voltage adds to the supply voltage |
| C. | Both (a) and (b) |
| D. | None of these |
| Answer» D. None of these | |
| 25. |
Number of PN junction in an SCR is |
| A. | Two |
| B. | Three |
| C. | Four |
| D. | Five |
| Answer» C. Four | |
| 26. |
In a single phase full wave rectifier, during blocking state the peak inversevoltage of diode is |
| A. | V m |
| B. | 2 V m |
| C. | V m / 2 |
| D. | 4 V m |
| Answer» C. V m / 2 | |
| 27. |
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 | |
| 28. |
A single-phase voltage controller, using one SCR in anti parallel with a diode, feeds a load R and Vs = 230 V. For a firing angel of 90° for the SCR, the PMMC voltage connected across R would read |
| A. | 0 |
| B. | 51.8 V |
| C. | –51.8 V |
| D. | –36.82 V |
| Answer» D. –36.82 V | |
| 29. |
he circuit in figure is for |
| A. | resonant commutation |
| B. | self commutation |
| C. | load commutation |
| D. | auxiliary commutation |
| Answer» C. load commutation | |
| 30. |
The power MOSFET device is a |
| A. | Current controlled unipolar device |
| B. | Voltage controlled unipolar device |
| C. | Current controlled bipolar device |
| D. | Voltage controlled bipolar device |
| Answer» C. Current controlled bipolar device | |
| 31. |
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 ) | |
| 32. |
In BJT, switching losses occurs |
| A. | Only at turn - on |
| B. | Only at turn - off |
| C. | Both at turn on and off |
| D. | None of these |
| Answer» D. None of these | |
| 33. |
In dual converters, |
| A. | Both rectifiers provides positive current to the load |
| B. | Both rectifiers provide negative current to the load |
| C. | One rectifiers provide positive current to the load and the other negative current |
| D. | One rectifier provide positive current to the source and the other negative |
| Answer» B. Both rectifiers provide negative current to the load | |
| 34. |
In a step down chopper, if Vs = 100 V and the chopper is operated at a dutycycle of 75 %. Find the output voltage. |
| A. | 100 V |
| B. | 75 V |
| C. | 25 V |
| D. | none of the mentioned |
| Answer» C. 25 V | |
| 35. |
The average value of the output voltage in a step - down dc chopper is givenby |
| A. | V 0 = V s |
| B. | V 0 = D V s |
| C. | V 0 = V s / D |
| D. | V 0 = V s / ( 1 - D ) |
| Answer» C. V 0 = V s / D | |
| 36. |
In arc rectifiers mercury is chosen as the liquid for rectifier because |
| A. | it has low specific heat |
| B. | it has low ionization potential |
| C. | it has high atomic weight |
| D. | all of the above. |
| Answer» E. | |
| 37. |
Very large values of modulation index (greater than 3.24) lead to |
| A. | Square AC output voltage |
| B. | Sine AC output voltage |
| C. | Triangular AC output voltage |
| D. | Trapezoidal AC output voltage |
| Answer» B. Sine AC output voltage | |
| 38. |
Thyristors connected in series need static and dynamic stabilizingcircuits. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 39. |
In a load commutated DC - DC chopper, the capacitor has a |
| A. | Symmetric triangular voltage across itself |
| B. | Symmetric rectangular voltage across itself |
| C. | Symmetric trapezoidal voltage across itself |
| D. | Symmetric sinusoidal voltage across itself |
| Answer» D. Symmetric sinusoidal voltage across itself | |
| 40. |
What is the formula for output voltage for Boost converter? |
| A. | 8D×Vin |
| B. | 5D×Vin |
| C. | 2D×Vin |
| D. | D×Vin |
| Answer» E. | |
| 41. |
The single phase bridge type cycloconverter uses __________ number ofSCRs. |
| A. | 4 |
| B. | 8 |
| C. | 6 |
| D. | none of the mentioned |
| Answer» B. 8 | |
| 42. |
For bidirectional operation of converters |
| A. | A parallel combination of controllable switch and a diode is used |
| B. | A parallel combination of controllable switch and capacitor is used |
| C. | A series combination of controllable switch and a diode is used |
| D. | A series combination of controllable switch and a capacitor is used |
| Answer» B. A parallel combination of controllable switch and capacitor is used | |
| 43. |
A forward voltage can be applied to an SCR after its: |
| A. | anode current reduces to zero |
| B. | gate recovery time |
| C. | reverse recovery time |
| D. | anode voltage reduces to zero |
| Answer» C. reverse recovery time | |
| 44. |
In mercury arc rectifiers the voltage drop in arc is nearly |
| A. | 0.1 volt per centimeter of arc length |
| B. | 1 volt per centimeter of arc length |
| C. | 10 volts per centimeter of arc length |
| D. | 12 to 15 volts per centimeter of arc length. |
| Answer» D. 12 to 15 volts per centimeter of arc length. | |
| 45. |
Inductor and Capacitor in Buck converter are used to ___________ |
| A. | Increase the cost |
| B. | Decrease the cost |
| C. | Filter out the harmonics |
| D. | Increase the harmonics |
| Answer» D. Increase the harmonics | |
| 46. |
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. | |
| 47. |
A single phase half wave converter is used to charge a battery of 50V. The thyristor is continuously fired by dc signal. Input voltage is v = Vm sin ωt. The thyristor will conduct |
| A. | from 0 to 180° |
| B. | when v > 50 V |
| C. | from 0 to 90° |
| D. | When v < 50 V |
| Answer» C. from 0 to 90° | |
| 48. |
An SCR can be used |
| A. | as static conductor |
| B. | for power control |
| C. | for speed control of dc shunt motor |
| D. | all of these |
| Answer» E. | |
| 49. |
Bidirectional semiconductor device is |
| A. | Diode |
| B. | BJT |
| C. | SCR |
| D. | TRIAC |
| Answer» E. | |
| 50. |
Gold doped GTOs have _____________ as compared to the conventionalGTOs |
| A. | high turn-off time |
| B. | low negative gate current requirement |
| C. | low reverse voltage blocking capabilities |
| D. | lower positive gate current requirement |
| Answer» C. low reverse voltage blocking capabilities | |