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MCQOPTIONS
This section includes 451 Mcqs, each offering curated multiple-choice questions to sharpen your ENGINEERING SERVICES EXAMINATION (ESE) knowledge and support exam preparation. Choose a topic below to get started.
| 351. |
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. | 15√2 A |
| C. | 15/√2 A |
| D. | 30 A |
| Answer» B. 15√2 A | |
| 352. |
Two thyristor of same rating and same specifications |
| A. | will have equal turn on and turn off periods |
| B. | will have equal turn on but unequal turn off periods |
| C. | may have equal or unequal turn on and turn off periods |
| D. | will have unequal turn on and turn off periods |
| Answer» D. will have unequal turn on and turn off periods | |
| 353. |
In the circuit of figure, the load current when thyristor is off |
| A. | is constant |
| B. | increases exponentially |
| C. | decreases exponentially |
| D. | zero |
| Answer» D. zero | |
| 354. |
In a single phase full bridge converter (B - 2 connection), the input voltage is v = Vm sin ωt. The output dc voltage for resistive load |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 355. |
A 3 phase fully controlled bridge converter is fed by a 3 phase system having phase voltage v = Vm sin ωt. The firing angle is a. The dc output voltage is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 356. |
An n pulse rectifier is fed by a source having an inductance L. If load current is I₀, the voltage drop due to overlap is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 357. |
A thyristor needs protection against |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 358. |
In the below figure the rms voltage across each half of secondary is 200 V. The peak inverse voltage across each of thyristor is |
| A. | 200 V |
| B. | √2(200) V |
| C. | √2(400) V |
| D. | 800 V |
| Answer» D. 800 V | |
| 359. |
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 | |
| 360. |
Two semiconverters are connected in series to form a single phase series converter. The input v = Vm sin ωt and α1 = α2 are the firing angles of the two converters. If α1 = α2 = 0, the dc output voltage is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» D. D | |
| 361. |
Assertion (A): The surge current which an SCR can withstand is much higher than rms on state current.Reason (R): The duration of surge current is very small. |
| 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 | |
| 362. |
In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally |
| A. | equal |
| B. | different |
| C. | equal or different |
| D. | different but sometimes equal |
| Answer» B. different | |
| 363. |
A single phase half wave controlled rectifier circuit is feeding on RL load. The circuit has a freewheeling diode. The input voltage is v = Vm sin ωt. If I0 is the load current during the conduction of freewheeling diode, the KVL equation during the conduction of free wheeling diode is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» C. C | |
| 364. |
In a single phase full wave regulator feeding an R-L load, the power factor angle of load is θ. The range of control of firing angle α is |
| A. | 0 ≤ α ≤ π |
| B. | θ ≤ α ≤ π |
| C. | 0 ≤ α ≤ (π - θ) |
| D. | θ ≤ α ≤ (π + θ) |
| Answer» C. 0 ≤ α ≤ (π - θ) | |
| 365. |
In a three phase to single phase full wave bridge cycloconverter, the number of thyristors is |
| A. | 36 |
| B. | 18 |
| C. | 12 |
| D. | 8 |
| Answer» D. 8 | |
| 366. |
A single phase fully controlled bridge rectifier is fed by a source having inductance. The output voltage during overlap period is |
| A. | Vm |
| B. | 0.5 Vm |
| C. | zero |
| D. | 0.5 Vm - voltage drop across inductance |
| Answer» D. 0.5 Vm - voltage drop across inductance | |
| 367. |
When a UJT is used as a relaxation oscillator the current should be |
| A. | less than Ip |
| B. | more than Iv |
| C. | more than Ip but less than Iv |
| D. | negative |
| Answer» D. negative | |
| 368. |
In a single phase full wave regulator feeding R-L load, the minimum firing angle can be zero. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 369. |
Assertion (A): The turn on time of SCR is about 1 to 4 ms.Reason (R): The turn off time of SCR is about 10 to 300 ms. |
| 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 | |
| 370. |
The number of gates in an SCR is |
| A. | 1 |
| B. | 3 |
| C. | 4 |
| D. | 6 |
| Answer» B. 3 | |
| 371. |
Assertion (A): A half wave controlled rectifier has poorer efficiency and higher ripple factor than a full wave controlled rectifier.Reason (R): The use of a freewheeling diode in half wave controlled rectifier circuit improves the waveform of load current and circuit power factor. |
| 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 | |
| 372. |
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 | |
| 373. |
The efficiency of a chopper circuit is about |
| A. | 80% or more |
| B. | around 50% |
| C. | around 20% |
| D. | around 5% |
| Answer» B. around 50% | |
| 374. |
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 | |
| 375. |
Which of the following is not between F2 layer and D layer? |
| A. | E layer |
| B. | F1 layer |
| C. | G region |
| D. | All of the above |
| Answer» D. All of the above | |
| 376. |
The symbol in figure is for |
| A. | SUS |
| B. | SBS |
| C. | Shockley diode |
| D. | UJT |
| Answer» D. UJT | |
| 377. |
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 | |
| 378. |
A bridge type single phase cycloconverter changes the frequency f to f/3. Then one half wave of output contains |
| A. | 3 full waves of input |
| B. | 3 half waves of input |
| C. | 6 full waves of input |
| D. | 6 half waves of input |
| Answer» C. 6 full waves of input | |
| 379. |
A single phase full wave regulator feeds R-L load. The best gating signal is |
| A. | short duration pulses |
| B. | long duration pulses |
| C. | pulse train |
| D. | either (a) or (b) |
| Answer» D. either (a) or (b) | |
| 380. |
In a circuit using a full wave converter (M - 2 connection) the PIV of each thyristor is 400 V. For the same output voltage and fully controlled bridge converter, PIV will be |
| A. | 400 V |
| B. | 800 V |
| C. | 200 V |
| D. | 200√2 V |
| Answer» D. 200√2 V | |
| 381. |
In a three phase series inverter, the firing frequency is |
| A. | three times output frequency |
| B. | six times output frequency |
| C. | twice the output frequency |
| D. | equal to output frequency |
| Answer» C. twice the output frequency | |
| 382. |
Which of the following is correct for a BJT? |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 383. |
Assertion (A): If the duty cycle of chopper is low the current would not become discontinuousReason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous. |
| 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 | |
| 384. |
The main utility of SCR is due to |
| A. | gate triggering |
| B. | high temperature triggering |
| C. | dv/dt triggering |
| D. | high breakdown voltage |
| Answer» B. high temperature triggering | |
| 385. |
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 | |
| 386. |
The commutation method in an inverter, is |
| A. | line commutation |
| B. | forced commutation |
| C. | either (a) or (b) |
| D. | none of the above |
| Answer» D. none of the above | |
| 387. |
For an illumination control circuit it is advisable to use a matched TRIAC-DIAC pair. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 388. |
In a thyristor, the forward breakover voltage |
| A. | is constant |
| B. | may be constant or may depend on gate current |
| C. | decreases as gate current is increased |
| D. | increases as gate current is increased |
| Answer» D. increases as gate current is increased | |
| 389. |
A single phase bridge type cycloconverter uses eight thyristors. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 390. |
In a single phase cycloconverter with centre tapped transformer |
| A. | all thyristors carry currents for equal duration |
| B. | the durations of currents in all thyristors may or may not be equal |
| C. | the durations of currents in all thyristors cannot be equal |
| D. | the duration of currents in all thyristors must be equal for satisfactory operation |
| Answer» C. the durations of currents in all thyristors cannot be equal | |
| 391. |
Thyristors connected in series need static and dynamic stabilizing circuits. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» B. False | |
| 392. |
In a single phase semi-converter the number of thyristors is |
| A. | 16 |
| B. | 8 |
| C. | 4 |
| D. | 2 |
| Answer» E. | |
| 393. |
Which of these devices have four layers? |
| A. | UJT |
| B. | SCR |
| C. | TRIAC |
| D. | SCR and TRIAC |
| Answer» C. TRIAC | |
| 394. |
In 180° mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time. |
| A. | True |
| B. | False |
| C. | May be True or False |
| D. | Can't say |
| Answer» C. May be True or False | |
| 395. |
In rectifier circuits, ripple factor RF and form factor FF are related as |
| A. | RF = (FF² - 1)^0.5 |
| B. | RF = FF |
| C. | RF = FF - 1 |
| D. | RF = (FF - 1)^0.5 |
| Answer» B. RF = FF | |
| 396. |
Assertion (A): The gate current of an SCR is always in the form of pulses. Reason (R): The gate losses, in pulse triggering, are low. |
| 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 | |
| 397. |
A thyristor has its gate current zero. To start conduction the forward voltage must exceed |
| A. | about 0.5 V |
| B. | forward breakover voltage |
| C. | on state voltage |
| D. | peak working off state forward voltage |
| Answer» C. on state voltage | |
| 398. |
A thyristor has internal power dissipation of 40W and is operated at an ambient temperature of 20°C. If thermal resistance is 1.6° C/W, the junction temperature is |
| A. | 114°C |
| B. | 164°C |
| C. | 94° C |
| D. | 84° C |
| Answer» E. | |
| 399. |
If Ar and Ac are the amplitudes of reference and control signals, the modulation index M is |
| A. | A |
| B. | B |
| C. | C |
| D. | D |
| Answer» B. B | |
| 400. |
In rectifier circuits, the rms value of ac component of output voltage is equal to |
| A. | Vrms |
| B. | 0.5 Vrms |
| C. | (Vrms - Vdc)²0.5 |
| D. | (Vrms² - Vdc²)^0.5 |
| Answer» E. | |