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MCQOPTIONS
This section includes 9294 Mcqs, each offering curated multiple-choice questions to sharpen your Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 6851. |
Natural commutation can be used in : |
| A. | DC circuits only |
| B. | AC circuits only |
| C. | both AC and DC circuits |
| D. | none of the above |
| Answer» C. both AC and DC circuits | |
| 6852. |
A single phase half wave rectifier circuit has a free wheeling diode. The free wheeling diode will conduct only if |
| A. | load is purely resistive |
| B. | load is purely inductive |
| C. | load is combination of R and L |
| D. | load is purely inductive or combination of R and L |
| Answer» E. | |
| 6853. |
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 | |
| 6854. |
If a step down chopper is fed by a dc voltage V with Ton and Toff are on and off periods then is |
| A. | average output voltage |
| B. | rms output voltage |
| C. | average or rms output voltage depending on load |
| D. | neither of the above |
| Answer» B. rms output voltage | |
| 6855. |
In a thyristors are i = kva. The value of a is |
| A. | about 0.5 |
| B. | about 2 |
| C. | about 5 |
| D. | about 20 |
| Answer» D. about 20 | |
| 6856. |
In an ordinary thyristor |
| A. | turn on and turn off times are equal |
| B. | turn on time is more than turn off time |
| C. | turn off time is more than turn on time |
| D. | turn on time may be equal, less than or more than turn off time |
| Answer» D. turn on time may be equal, less than or more than turn off time | |
| 6857. |
A single phase bridge type cycloconverter uses eight thyristors. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 6858. |
A current source inverter has simple commutation circuit. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 6859. |
In load commutated chopper, the commutating element |
| A. | is capacitor |
| B. | is capacitor and inductor |
| C. | is capacitor, inductor and auxiliary thyristor |
| D. | any of the above depending on load |
| Answer» B. is capacitor and inductor | |
| 6860. |
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 | |
| 6861. |
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 | |
| 6862. |
In integral cycle control of ac regulators, the period of integral cycle control, i.e., (m + n) T should be |
| A. | less than mechanical or thermal time constant of the system |
| B. | more than the mechanical or thermal time constant of the system |
| C. | more or less than the mechanical or thermal time constant |
| D. | very high |
| Answer» B. more than the mechanical or thermal time constant of the system | |
| 6863. |
UJT can be used for |
| A. | firing an SCR |
| B. | turning off an SCR |
| C. | both firing and turning off an SCR |
| D. | none of the above |
| Answer» B. turning off an SCR | |
| 6864. |
In the circuit of figure, the waveshape of load current when thyristor conducting is |
| A. | constant |
| B. | increasing exponentially |
| C. | decreasing exponentially |
| D. | either (b) or (c) |
| Answer» C. decreasing exponentially | |
| 6865. |
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 | |
| 6866. |
Which of the following devices exhibit negative resistance characteristics? |
| A. | UJT |
| B. | PUT |
| C. | Both UJT and PUT |
| D. | UJT, PUT and SBS |
| Answer» D. UJT, PUT and SBS | |
| 6867. |
All other parameters remaining the same, a 3 phase bridge inverter with 180 mode of operation |
| A. | has the same peak thyristor current as in 120 mode of operation |
| B. | has higher peak thyristor current than in 120 mode of operation |
| C. | has lower peak thyristor current than in 120 mode of operation |
| D. | any of the above |
| Answer» C. has lower peak thyristor current than in 120 mode of operation | |
| 6868. |
As compared to BJT, MOSFET has |
| A. | lower switching losses and higher conduction losses |
| B. | higher switching losses and higher conduction losses |
| C. | higher switching losses and lower conduction losses |
| D. | lower switching losses and lower conduction losses |
| Answer» B. higher switching losses and higher conduction losses | |
| 6869. |
In a series inverter supplying a load resistance R, the commutating elements L and C should be such that |
| A. | <img src="/_files/images/electronics-and-communication-engineering/power-electronics/268-58-1.png"> |
| B. | <img src="/_files/images/electronics-and-communication-engineering/power-electronics/268-58-2.png"> |
| C. | <img src="/_files/images/electronics-and-communication-engineering/power-electronics/267-35-2.png"> |
| D. | <img src="/_files/images/electronics-and-communication-engineering/power-electronics/267-35-3.png"> |
| Answer» C. <img src="/_files/images/electronics-and-communication-engineering/power-electronics/267-35-2.png"> | |
| 6870. |
Which of these commutation methods uses an auxiliary SCR? |
| A. | Class A |
| B. | Class B |
| C. | Class C |
| D. | Class D |
| Answer» D. Class D | |
| 6871. |
Two semiconverters are connected in series to form a single phase series converter. The input v = Vm sin t and a1 = a2 are the firing angles of the two converters. If a1 = a2 = 0, the dc output voltage is |
| A. | <img src="/_files/images/electronics-and-communication-engineering/power-electronics/267-52-2.png"> |
| B. | <img src="/_files/images/electronics-and-communication-engineering/power-electronics/267-52-1.png"> |
| C. | <img src="/_files/images/electronics-and-communication-engineering/power-electronics/278-273-1.png"> |
| D. | <img src="/_files/images/electronics-and-communication-engineering/power-electronics/278-273-2.png"> |
| Answer» D. <img src="/_files/images/electronics-and-communication-engineering/power-electronics/278-273-2.png"> | |
| 6872. |
In integral cycle control the period of on-off control should be more than mechanical time constant of load. |
| A. | True |
| B. | False |
| Answer» C. | |
| 6873. |
Assertion (A): A high dv/dt may cause triggering of a thyristor.Reason (R): A high dv/dt results in charging current in the thyristor. |
| 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 | |
| 6874. |
When the core of a saturable reactor is saturated, the inductance is high. |
| A. | True |
| B. | False |
| Answer» C. | |
| 6875. |
In controlled heating circuits, thyristors act as |
| A. | rectifier |
| B. | inverter |
| C. | ac regulator |
| D. | chopper |
| Answer» D. chopper | |
| 6876. |
HVDC transmission systems generally use |
| A. | 12 pulse converters |
| B. | 6 pulse converters |
| C. | 3 pulse converters |
| D. | either 12 or 6 pulse converters |
| Answer» B. 6 pulse converters | |
| 6877. |
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 | |
| 6878. |
In a 3 phase full converter the average load current is 150 A. The average thyristor current is |
| A. | 150 A |
| B. | 75A |
| C. | 50 A |
| D. | 25 A |
| Answer» D. 25 A | |
| 6879. |
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 | |
| 6880. |
A cycloconverter is |
| A. | ac-dc converter |
| B. | dc-ac converter |
| C. | dc-dc converter |
| D. | ac-ac converter |
| Answer» E. | |
| 6881. |
The number of leads in a power semiconductor diode are |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 2 or 3 |
| Answer» B. 3 | |
| 6882. |
Assertion (A): A dual converter may be circulating current type or non circulating current type.Reason (R): In circulating current dual converter only one converter can be operated at one time. |
| 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 | |
| 6883. |
Current chopping leads to |
| A. | over voltage |
| B. | over current |
| C. | both over voltage and over current |
| D. | either over voltage or over current |
| Answer» B. over current | |
| 6884. |
A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 &ohm; 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 | |
| 6885. |
In an SCR, the anode current is controlled by |
| A. | gate current only |
| B. | external circuit only |
| C. | both gate current and external circuit |
| D. | none of the above |
| Answer» C. both gate current and external circuit | |
| 6886. |
A single phase half wave converter is feeding a resistive load. Just before triggering, the voltage across thyristor is |
| A. | zero |
| B. | about 1 V |
| C. | same as input voltage |
| D. | twice the input voltage |
| Answer» D. twice the input voltage | |
| 6887. |
The number of doped regions in a SCR is |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 5 |
| Answer» D. 5 | |
| 6888. |
All inverters use forced commutation. |
| A. | True |
| B. | False |
| Answer» C. | |
| 6889. |
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 | |
| 6890. |
An SBS can conduct is one direction only. |
| A. | True |
| B. | False |
| Answer» C. | |
| 6891. |
In 180 mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time. |
| A. | True |
| B. | False |
| Answer» C. | |
| 6892. |
A reactor is used in a dual converter operating in non-circulating current mode. |
| A. | True |
| B. | False |
| Answer» C. | |
| 6893. |
In a single phase full wave ac regulator the rms value of load current is 20 A load is purely resistive. Then |
| A. | average thyristor current will be less than 20 A but rms thyristor current will be more than 20 A |
| B. | both the average and rms thyristor currents will be less than 20 A |
| C. | both the average and rms thyristor currents will be more than 20 A |
| D. | rms thyristor current will be 20 A and average thyristor current will be 10 A |
| Answer» C. both the average and rms thyristor currents will be more than 20 A | |
| 6894. |
A 750 A circuit uses thyristor of current rating 175 A. If derating is 25%, the number of thyristors in parallel is |
| A. | 3 |
| B. | 4 |
| C. | 6 |
| D. | 10 |
| Answer» D. 10 | |
| 6895. |
Assertion (A): An inverter does not require forced commutation Reason (R): A series inverter is a forced commutation inverter. |
| 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» E. | |
| 6896. |
A thyristor has maximum allowable junction temperature of 110 C and the ambient temperature is 40 C, If the maximum internal power dissipation is 50 W, the thermal resistance is |
| A. | 2 C/W |
| B. | 1.4 C/W |
| C. | 0.7 C/W |
| D. | 2.2 C/W |
| Answer» C. 0.7 C/W | |
| 6897. |
The symbol in figure is for |
| A. | DIAC |
| B. | P-N junction diode |
| C. | Schottky diode |
| D. | None of the above |
| Answer» D. None of the above | |
| 6898. |
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 | |
| 6899. |
The number of gates in an SCR is |
| A. | 1 |
| B. | 3 |
| C. | 4 |
| D. | 6 |
| Answer» B. 3 | |
| 6900. |
The waveshape of output voltage of half bridge inverter is |
| A. | sinusoidal |
| B. | square |
| C. | triangular |
| D. | either (a) or (b) |
| Answer» C. triangular | |