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.
| 351. |
In integral cycle control the period of on-off control should be more than mechanical time constant of load. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 352. |
Which of the following commutation methods is the overall circuit under damped? |
| A. | Class A |
| B. | Class B |
| C. | Class C |
| D. | Both class A and Class B |
| Answer» E. | |
| 353. |
The cut in voltages for germanium and silicon diodes respectively as |
| A. | 0.3 V and 0.7 V |
| B. | 0.7 V and 0.3 V |
| C. | 0.6 V and 0.9 V |
| D. | 0.5 V and 0.7 V |
| Answer» B. 0.7 V and 0.3 V | |
| 354. |
A 3 phase ac regulator uses |
| A. | 3 thyristors |
| B. | 6 thyristors |
| C. | 9 thyristors |
| D. | 12 thyristors |
| Answer» C. 9 thyristors | |
| 355. |
From which instant is the turn off time of a thyristor defined |
| A. | when anode voltage becomes zero |
| B. | when anode current becomes zero |
| C. | when both anode voltage and current become zero |
| D. | none of the above |
| Answer» C. when both anode voltage and current become zero | |
| 356. |
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 | |
| 357. |
Which chopper circuit operates in quadrants 1 and 4? |
| A. | A |
| B. | B |
| C. | D |
| D. | E |
| Answer» D. E | |
| 358. |
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 | |
| 359. |
An SUS is |
| A. | exactly similar to SCR but with higher rating |
| B. | similar to UJT |
| C. | PUT and avalanche diode connected in anti parallel |
| D. | SCR and avalanche diode connected in parallel |
| Answer» D. SCR and avalanche diode connected in parallel | |
| 360. |
In a 3 phase bridge inverter with 120° mode of operation the. number of thyristors conducting at one time are |
| A. | 1 |
| B. | 2 |
| C. | 3 |
| D. | 4 |
| Answer» C. 3 | |
| 361. |
A single phase half bridge inverter required to feed R-L loads needs |
| A. | 2 thyristors |
| B. | 4 thyristors |
| C. | 2 thyristors and two diodes |
| D. | 4 thyristors and 4 diodes |
| Answer» D. 4 thyristors and 4 diodes | |
| 362. |
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 | |
| 363. |
In a full bridge circuit supplying an RLC under damped circuit |
| A. | the waveshapes of output voltage and load current are square |
| B. | the waveshapes of output voltage and load current are sinusoidal |
| C. | the waveshapes of output voltage is square but the waveshape of load current is nearly sinusoidal |
| D. | none of the above |
| Answer» D. none of the above | |
| 364. |
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 | |
| 365. |
The gate current required to turn on an SCR is |
| A. | few amperes |
| B. | a few mA |
| C. | almost equal to anode current |
| D. | about 50% of anode current |
| Answer» C. almost equal to anode current | |
| 366. |
The effect of source inductance in a 3 phase fully controlled bridge converter is to |
| A. | decrease the output voltage |
| B. | increase the output voltage |
| C. | decrease the output voltage and increase the output current |
| D. | increase the output voltage and decrease the output current |
| Answer» B. increase the output voltage | |
| 367. |
A fully controlled bridge converter is feeding an RLE load. For some circuit conditions firing angle is 47°. If connections of battery are reversed, the firing angle is likely to be |
| A. | 47° |
| B. | less than 47° |
| C. | more than 47° |
| D. | either more or less than 47° |
| Answer» D. either more or less than 47¬∞ | |
| 368. |
A thyristor needs protection against |
| A. | high |
| B. | high |
| C. | both high and high |
| D. | either high or high |
| Answer» D. either high or high | |
| 369. |
A dc chopper V = 500 V feeds an electric fraction dc series motor. The chopping frequency is 400 Hz. The series inductance required to limit the maximum current swing to 10 A is |
| A. | 20 mH |
| B. | about 31 mH |
| C. | about 51 mH |
| D. | about 92 mH |
| Answer» C. about 51 mH | |
| 370. |
When a dc chopper feeds an RLE load, the load current, during steady state operation |
| A. | remains constant |
| B. | varies between maximum and minimum values |
| C. | may remain constant or vary |
| D. | is constant if R is constant |
| Answer» C. may remain constant or vary | |
| 371. |
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 | |
| 372. |
The number of leads in a power semiconductor diode are |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 2 or 3 |
| Answer» B. 3 | |
| 373. |
In a 3 phase semiconverter, the firing frequency is |
| A. | equal to line frequency |
| B. | 3 times the line frequency |
| C. | 6 times the line frequency |
| D. | 12 times the line frequency |
| Answer» C. 6 times the line frequency | |
| 374. |
A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be |
| A. | about 1350 rpm |
| B. | about 720 rpm |
| C. | about 360 rpm |
| D. | either (b) or (c) |
| Answer» C. about 360 rpm | |
| 375. |
The advantage of modified series inverter with two inductors and two capacitors is |
| A. | the intermittent operation of battery is avoided |
| B. | efficiency of circuit is more |
| C. | the output frequency is low |
| D. | all of the above |
| Answer» B. efficiency of circuit is more | |
| 376. |
As regards single phase dual converter |
| A. | the change in operation from one quadrant to the other is faster in non-circulating current mode |
| B. | the change in operation from one quadrant to the other is faster in circulating current mode |
| C. | the time response to change in operation from one quadrant to other is the same in both the modes |
| D. | the time response to change in operation from one quadrant to the other may be faster in any of the two modes |
| Answer» C. the time response to change in operation from one quadrant to other is the same in both the modes | |
| 377. |
A single phase electric heater uses phase controlled thyristors. The firing angle is 90°. The degree of heating is |
| A. | 25% of maximum |
| B. | 50% of maximum |
| C. | 75% of maximum |
| D. | none of the above |
| Answer» C. 75% of maximum | |
| 378. |
A high frequency series inverter consists of |
| A. | a number of series inverters in series |
| B. | a number of series inverters in parallel |
| C. | a number of parallel inverters in parallel |
| D. | a number of parallel inverters in series |
| Answer» C. a number of parallel inverters in parallel | |
| 379. |
The power factor at the input terminals of a cyclo- converter is generally |
| A. | low and leading |
| B. | low and lagging |
| C. | high and leading |
| D. | high and lagging |
| Answer» C. high and leading | |
| 380. |
In the below figure, the average value of load current is 15 A. The load is highly inductive. The peak value of thyristor current is |
| A. | 15 A |
| B. | 152 A |
| C. | |
| Answer» B. 152 A | |
| 381. |
A single phase full wave regulator feeds a resistive load. The firing angle of thyristors is 90°. The input power factor is |
| A. | 1 |
| B. | 0.707 lagging |
| C. | 0.5 lagging |
| D. | 0.2 lagging |
| Answer» C. 0.5 lagging | |
| 382. |
Induction heating systems require low frequency inverters. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 383. |
The use of free wheeling diode in controlled rectifier improves the waveshape of load current. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 384. |
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 | |
| 385. |
The minimum gate current which can turn on SCR is called : |
| A. | trigger current |
| B. | holding current |
| C. | junction current |
| D. | breakover current |
| Answer» B. holding current | |
| 386. |
Which inverter circuit uses coupled inductors? |
| A. | Modified McMurray full bridge inverter |
| B. | McMurray Bedford half bridge inverter |
| C. | Modified McMurray Bedford half bridge inverter |
| D. | Both (b) and (c) |
| Answer» E. | |
| 387. |
When the core of a saturable reactor is saturated, the inductance is high. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 388. |
Thyristors connected in series need : |
| A. | static equalizing circuit |
| B. | dynamic equalizing circuit |
| C. | both static and dynamic equalizing circuits |
| D. | none of the above |
| Answer» D. none of the above | |
| 389. |
When thyristors are connected in parallel, the current distribution may become non-uniform due to |
| A. | inductive effect of current carrying conductors |
| B. | capacitive effect of current carrying conductors |
| C. | both inductive and capacitive effects |
| D. | none of the above |
| Answer» B. capacitive effect of current carrying conductors | |
| 390. |
Assertion (A): Gate triggering is the most commonly used method for triggering of an SCR.Reason (R): Even a small gate current is sufficient to turn on an SCR. |
| 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 | |
| 391. |
Inverters find applications in |
| A. | HVDC transmission |
| B. | UPS |
| C. | variable speed ac drives |
| D. | all of the above |
| Answer» E. | |
| 392. |
A single phase fully controlled bridge converter is fed by a voltage Vm sin ωt. The average and rms values of output voltage are |
| A. | |
| B. | |
| Answer» B. | |
| 393. |
A fully controlled bridge converter can operate in quadrants |
| A. | 1 |
| B. | 1 and 2 |
| C. | 1 and 3 |
| D. | 1 and 4 |
| Answer» E. | |
| 394. |
For an illumination control circuit it is advisable to use a matched TRIAC-DIAC pair. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 395. |
It is possible to use a freewheeling diode in |
| A. | single phase half wave controlled rectifier as well as in single phase full wave controlled rectifier (M - 2 connection) |
| B. | single phase half wave controlled rectifier but not in single phase full wave controlled rectifier (M - 2 connection) |
| C. | single phase full wave controlled rectifier (M - 2 connection) but not in single phase half wave controlled rectifier |
| D. | all controlled rectifier circuits |
| Answer» E. | |
| 396. |
Thyristors connected in series need static and dynamic stabilizing circuits. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 397. |
The symbol in figure is for |
| A. | SUS |
| B. | SBS |
| C. | SCS |
| D. | Shockley diode |
| Answer» C. SCS | |
| 398. |
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 | |
| 399. |
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 | |
| 400. |
In sinusoidal PWM for inverters the width of different pulses are not the same. |
| A. | 1 |
| B. | |
| Answer» B. | |