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MCQOPTIONS
This section includes 227 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
In a flyback converter, the inductor of the buck-boost converter has been replaced by a |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 | |
| 2. |
The amount of dielectric heating is inversely proportional to frequency. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» C. none | |
| 3. |
In current commutated DC-DC choppers, the voltage spike appears across the 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 | |
| 4. |
Voltage commutation circuit can be converted into a current commutation by interchanging the positions of |
| A. | Diode and capacitor |
| B. | Capacitor and SCR |
| C. | Inductor and capacitor |
| D. | Capacitor and load |
| Answer» B. Capacitor and SCR | |
| 5. |
The advantage of using free - wheeling diode in half controlled bridge converter is that |
| A. | There is always a path for the dc current independent of the ac line |
| B. | There is always a path for the ac current independent of the ac line |
| C. | There is always a path for the dc current dependent of the ac line |
| D. | There is always a path for the ac current independent of the ac line |
| Answer» B. There is always a path for the ac current independent of the ac line | |
| 6. |
In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes |
| A. | Positive |
| B. | Negative |
| C. | Zero |
| D. | None of these |
| Answer» B. Negative | |
| 7. |
The input current waveform of a bridge controlled rectifier when the load is perfectly filtered is |
| A. | Sine wave |
| B. | Square wave |
| C. | Saw - tooth wave |
| D. | Trapezoidal wave |
| Answer» C. Saw - tooth wave | |
| 8. |
If all the SCR s of 3 phase PAC is replaced by diodes, they would be triggered |
| A. | 120 degree after the zero crossing of the corresponding line voltages |
| B. | 60 degree after the zero crossing of the corresponding line voltages |
| C. | 120 degree before the zero crossing of the corresponding line voltages |
| D. | 60 degree before the zero crossing of the corresponding line voltages |
| Answer» C. 120 degree before the zero crossing of the corresponding line voltages | |
| 9. |
A single phase step up cycloconverter changes 50 Hz to 100 Hz. Then one half wave of input will give rise to |
| A. | one half wave of output |
| B. | one full wave of output |
| C. | two full waves of output |
| D. | either (b) or (c) |
| Answer» C. two full waves of output | |
| 10. |
A thyristor is reverse biased. A positive gate pulse is applied. The thyristor |
| A. | will be turned on |
| B. | may or may not turn on |
| C. | will not turn on |
| D. | will turn on after sometime |
| Answer» D. will turn on after sometime | |
| 11. |
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 | |
| 12. |
The rated current of a thyristor is 40 A. The holding current will be about : |
| A. | 20 A |
| B. | 1 A |
| C. | 100 mA |
| D. | 10 mA |
| Answer» E. | |
| 13. |
In a circulating-current type of dual converter, the nature of the voltage across the reactor is: |
| A. | Alternating |
| B. | Pulsating |
| C. | Direct |
| D. | Triangular |
| Answer» B. Pulsating | |
| 14. |
A resistor connected across the gate and cathode of an SCR in a circuit increases its |
| A. | dv/dt rating |
| B. | Holding current |
| C. | Noise Immunity |
| D. | Turn-off time |
| Answer» D. Turn-off time | |
| 15. |
Once SCR starts conducting a forward current, its gate losses control over: |
| A. | anode circuit voltage only |
| B. | anode circuit current only |
| C. | anode circuit voltage and current |
| D. | none of the above |
| Answer» D. none of the above | |
| 16. |
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 | |
| 17. |
On state voltage drop across thyristor used in a 230 V supply system 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 | |
| 18. |
The input current waveform of a bridge controlled rectifier when the load is perfectly filtered is |
| A. | Sine wave |
| B. | Square wave |
| C. | Saw tooth wave |
| D. | Trapezoidal wave |
| Answer» C. Saw tooth wave | |
| 19. |
If T is the time period for a chopper circuit and is its duty cycle, then the chopping frequency is |
| A. | Ton/ |
| B. | Toff/ |
| C. | /Toff |
| D. | /Ton |
| Answer» E. | |
| 20. |
A GTO can be represented by two transistors T1 & T2. The current gain of both transistors are 1 and 2 respectively. A low value of gate current requires |
| A. | low value of 1 and 2 |
| B. | low value of 1 and high value of 2 |
| C. | high value of 1 and low value of 2 |
| D. | high values of 1 and 2 |
| Answer» C. high value of 1 and low value of 2 | |
| 21. |
Latching current for the GTOs is ________ as compared to CTs (Conventional thyristors). |
| A. | more |
| B. | less |
| C. | constant |
| D. | cannot be said |
| Answer» B. less | |
| 22. |
In ac - dc conversion, when the switch is closed then the sum of voltages around the loop is |
| A. | Zero |
| B. | Non zero |
| C. | Equal to the sum of voltage when switch is open |
| D. | Twice of the voltage when switch is open |
| Answer» C. Equal to the sum of voltage when switch is open | |
| 23. |
Gold doped GTOs have _____________ as compared to the conventional GTOs |
| 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 | |
| 24. |
In case of the two-transistor model (T1 & T2) of GTO with anode-short, the anode-short is placed between the |
| A. | emitter of T1 & T2 |
| B. | emitter of T1 & base of T2 |
| C. | emitter of T1 & base of T1 |
| D. | emitter of T1 & collector of T2 |
| Answer» D. emitter of T1 & collector of T2 | |
| 25. |
Choose the correct statement: GTOs have _________ as compared to the CTs. |
| A. | less on-state voltage drop |
| B. | less gate drive losses |
| C. | higher reverse blocking capabilities |
| D. | faster switching speed |
| Answer» E. | |
| 26. |
In a single phase full wave rectifier, during blocking state the peak inverse voltage of diode is |
| A. | V m |
| B. | 2 V m |
| C. | V m / 2 |
| D. | 4 V m |
| Answer» C. V m / 2 | |
| 27. |
The sum of all phase current in a star connected primary winding with no neutral connection is equal to |
| A. | Phase current |
| B. | Three times the phase current |
| C. | Three times the line current |
| D. | Zero at all times |
| Answer» E. | |
| 28. |
In BJT, the forward biased base emitter junction inject holes from base to emitter, the holes |
| A. | Do not contribute to the collector current |
| B. | Result in net current flow component into the base |
| C. | Contribute to the collector current |
| D. | Only (a) and (b) |
| Answer» E. | |
| 29. |
For 3 phase rotary converters, when power factor is unity. the ac line to dc current ratio is |
| A. | 1.5 |
| B. | 1.1 |
| C. | 1.0 |
| D. | 0.942. |
| Answer» E. | |
| 30. |
The average value of the output voltage in a step - down dc chopper is given by |
| 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 | |
| 31. |
To detect an over - current fault condition, the most reliable method is to connect a |
| A. | Current sensor across IGBT |
| B. | Voltage sensor across IGBT |
| C. | Current sensor in series with IGBT |
| D. | Voltage sensor in series with IGBT |
| Answer» E. | |
| 32. |
The IGBT resulted in higher switching speed and lower energy losses. It can be used for |
| A. | Uninterruptible power supplies |
| B. | Induction heating system |
| C. | Constant voltage and frequency power supplies |
| D. | All of these |
| Answer» D. All of these | |
| 33. |
With gate open, the maximum anode current at which SCR is turned off from ON condition is called |
| A. | breakdown voltage |
| B. | peak reverse voltage |
| C. | holding current |
| D. | latching current |
| Answer» E. | |
| 34. |
The curve between V and I of SCR when anode is positive w.r.t cathode and when anode is negative w.r.t cathode are known as |
| A. | both as forward characteristics |
| B. | both as reverse characteristics |
| C. | former as forward characteristics and later as reverse characteristics |
| D. | former as reverse characteristics and later as forward characteristics |
| Answer» D. former as reverse characteristics and later as forward characteristics | |
| 35. |
Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of |
| A. | AC input power to the transformer volt - amp rating required by secondary |
| B. | AC input power to the transformer volt - amp rating required by primary |
| C. | DC output power to the transformer volt - amp rating required by secondary |
| D. | DC output power to the transformer volt - amp rating required by primary |
| Answer» D. DC output power to the transformer volt - amp rating required by primary | |
| 36. |
The single phase bridge type cycloconverter uses __________ number of SCRs. |
| A. | 4 |
| B. | 8 |
| C. | 6 |
| D. | none of the mentioned |
| Answer» B. 8 | |
| 37. |
The single phase mid-point type cycloconverter uses __________ number of SCRs. |
| A. | 4 |
| B. | 8 |
| C. | 6 |
| D. | none of the mentioned |
| Answer» B. 8 | |
| 38. |
During forward blocking state of SCR, the voltage and current respectively are |
| A. | high and high |
| B. | low and low |
| C. | high and low |
| D. | low and high |
| Answer» D. low and high | |
| 39. |
In sinusoidal PWM for inverters the width of different pulses are not the same. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» B. False | |
| 40. |
A thyristor has a turn on time of 6 s. If the anode circuit is inductive, the turn on time will be |
| A. | 6 s |
| B. | less than 6 s |
| C. | more than 6 s |
| D. | either 6 s or less |
| Answer» D. either 6 s or less | |
| 41. |
In the method of phase control, the phase relationship between ___ & ___ is controlled 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 | |
| 42. |
Find the output voltage for a step-up chopper when it is operated at a duty cycle of 50 % and Vs = 240 V. |
| A. | 240 V |
| B. | 480 V |
| C. | 560 V |
| D. | 120 V |
| Answer» C. 560 V | |
| 43. |
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 | |
| 44. |
A single-phase half-wave thyristor circuit with R load is triggered at an angle of = 0 . As such, the maximum value of the average output voltage would be given by Consider Vs = Vm sin t. |
| A. | Vm |
| B. | 2Vm/ |
| C. | Vm/ |
| D. | Vm/ |
| Answer» D. Vm/ | |
| 45. |
Find the expression for output voltage for a step-up chopper, assume linear variation of load current and as the duty cycle. |
| A. | Vs |
| B. | Vs/ |
| C. | Vs/(1- ) |
| D. | Vs/ 2 |
| Answer» D. Vs/ 2 | |
| 46. |
In a step down chopper, if Vs = 100 V and the chopper is operated at a duty cycle of 75 %. Find the output voltage. |
| A. | 100 V |
| B. | 75 V |
| C. | 25 V |
| D. | none of the mentioned |
| Answer» C. 25 V | |
| 47. |
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 | |
| 48. |
On load tap changer using thyristors can have a maximum of two taps. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» C. none | |
| 49. |
In a single phase full wave regulator feeding a resistive load, the average current over one full cycle |
| A. | is always zero |
| B. | cannot be zero |
| C. | may be sometimes zero |
| D. | is always positive |
| Answer» B. cannot be zero | |
| 50. |
In a single phase half-wave thyristor circuit with R load & Vs=Vm sin t, 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 | |