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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.
| 501. |
The total number of leads in reverse conducting thyristor is |
| A. | 2 |
| B. | 3 |
| C. | 1 |
| D. | 4 |
| Answer» C. 1 | |
| 502. |
The dynamic equalising circuit consists of a series combination of capacitor C and resistor RC across each thyristor. This resistance RC (along with parallel connected diode) |
| A. | limits charging current |
| B. | limits discharging current |
| C. | limits both charging and discharging currents |
| D. | none of the above |
| Answer» C. limits both charging and discharging currents | |
| 503. |
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 | |
| 504. |
In a 3 phase full wave regulator feeding resistance load connected in star, the possible range of firing angle a is |
| A. | 0 ≤ a ≤ 180° |
| B. | 0 ≤ a ≤ 150° |
| C. | 0 ≤ a ≤ 120° |
| D. | 0 ≤ a ≤ 90° |
| Answer» C. 0 ‚⧠a ‚⧠120¬∞ | |
| 505. |
A semi converter operates in two quadrants. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 506. |
A current source inverter has simple commutation circuit. |
| A. | 1 |
| B. | |
| C. | is capacitor |
| D. | is capacitor and inductor |
| Answer» B. | |
| 507. |
In a single phase full wave regulator feeding R-L load, the minimum firing angle can be zero. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 508. |
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 | |
| 509. |
A single phase semiconverter is feeding a highly inductive load and has freewheeling diode across the load. The waveshapes of output voltage and output current |
| A. | are similar |
| B. | are not similar |
| C. | may be similar or dissimilar |
| D. | are similar only if firing angle is zero |
| Answer» C. may be similar or dissimilar | |
| 510. |
Which of these commutation methods uses two leads? |
| A. | Class A |
| B. | Class B |
| C. | Class C |
| D. | Class D |
| Answer» E. | |
| 511. |
Assertion (A): A GTO can be turned on and turned off by gate pulses Reason (R): A GTO can be turned off by negative gate pulse. |
| 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 | |
| 512. |
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 | |
| 513. |
In a 3 phase semiconverter, the dc output voltage for a certain firing angle is 50% of the maximum possible value. The firing angle is |
| A. | 30° |
| B. | 60° |
| C. | 90° |
| D. | 120° |
| Answer» D. 120¬∞ | |
| 514. |
In a semi converter feeding a resistive load, |
| A. | the waveshapes of input voltage and input current are always similar |
| B. | the waveshapes of input voltage and input current can never be similar |
| C. | the waveshapes of input voltage and input current are similar only if firing angle is zero |
| D. | the waveshapes of input voltage and input current are similar only if firing angle is high |
| Answer» D. the waveshapes of input voltage and input current are similar only if firing angle is high | |
| 515. |
In a single phase semi-converter the number of thyristors is |
| A. | 16 |
| B. | 8 |
| C. | 4 |
| D. | 2 |
| Answer» E. | |
| 516. |
A crowbar circuit is generally needed for protection under fault conditions. |
| A. | 1 |
| B. | |
| C. | the maximum rate of rise of anode voltage which will trigger the SCR |
| D. | the maximum rate of rise of anode voltage which will not trigger the SCR if gate signal is applied |
| Answer» B. | |
| 517. |
A cycloconverter is a group of controlled rectifiers. |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | 0.707 lagging |
| Answer» B. | |
| 518. |
A step up chopper can give an output voltage |
| A. | higher than input voltage |
| B. | lower than input voltage |
| C. | both higher and lower input voltage |
| D. | all of the above |
| Answer» B. lower than input voltage | |
| 519. |
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 | |
| 520. |
Surge current rating of an SCR is |
| A. | the maximum repetitive surge current in which the SCR can withstand |
| B. | the maximum non-repetitive surge current in which the SCR can withstand |
| C. | the maximum repetitive or non repetitive surge current in which the SCR can withstand |
| D. | the maximum surge current in which the SCR can withstand if both surge current and steady current exist together |
| Answer» C. the maximum repetitive or non repetitive surge current in which the SCR can withstand | |
| 521. |
A dc chopper is feeding an RLE load. The current can become discontinuous if |
| A. | is high |
| B. | a is low |
| C. | E is high |
| D. | none of the above |
| Answer» E. | |
| 522. |
Assertion (A): Inverters and choppers use fast switching thyristors Reason (R): Fast switching SCR has low turn off 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» B. Both A and R correct but R is not correct explanation of A | |
| 523. |
For a BJT a = 0.98, then β = |
| A. | 0.02 |
| B. | 0.5 |
| C. | 4.9 |
| D. | 48 |
| Answer» E. | |
| 524. |
A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When a = 0, speed is 600 rpm. If a = 90°, the speed is likely to be |
| A. | about 300 rpm |
| B. | about 150 rpm |
| C. | about 75 rpm |
| D. | about zero |
| Answer» B. about 150 rpm | |
| 525. |
The load circuit of a single phase full bridge inverter |
| A. | must be underdamped |
| B. | must be overdamped |
| C. | may be underdamped or overdamped |
| D. | may be any type of load |
| Answer» E. | |
| 526. |
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 | |
| 527. |
A single phase half wave rectifier is feeding a resistive load. Input voltage v = Vm sin ωt. The output dc voltage is Vdc and output rms voltage is Vrms . If firing angle is 180°, Vdc and Vrms respectively are |
| A. | 0 and 0 |
| B. | |
| Answer» B. | |
| 528. |
If the frequency is less than the damped frequency in a series- inverter |
| A. | the distortion of output voltage waveform is low |
| B. | the distortion of output voltage waveform is high |
| C. | the distortion of output voltage may be high or low depending on the load impedance |
| D. | none of the above |
| Answer» C. the distortion of output voltage may be high or low depending on the load impedance | |
| 529. |
Assertion (A): A transistor requires a continuous base signal for conduction but a thyristor requires a gate pulse.Reason (R): Transistor find widespread application in power electronic circuits. |
| 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 | |
| 530. |
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 | |
| 531. |
A 3 kV circuit uses SCR of 800 V rating. If derating is 25%, the number of SCRs in series is |
| A. | 4 |
| B. | 5 |
| C. | 6 |
| D. | 8 |
| Answer» C. 6 | |
| 532. |
In a half bridge inverter, the freewheeling diodes are needed |
| A. | even when load is resistive |
| B. | only when load is inductive |
| C. | only when load is inductive or capacitive |
| D. | for all types of loads |
| Answer» D. for all types of loads | |
| 533. |
If Vdc1 is the dc output voltage in half wave controlled rectifier circuit feeding resistive load and Vdc2 is the dc output voltage in full wave controlled rectifier circuit (M - 2 connection) feeding resistive load, then |
| A. | Vdc1 = 0.5 Vdc2 for all values of firing angle |
| B. | Vdc1 = Vdc2 for all values of firing angle |
| C. | Vdc1 ≤ 0.5 Vdc2 for all values of firing angle |
| D. | Vdc1 ‚â• 0.5 Vdc2 for all values of firing angle |
| Answer» B. Vdc1 = Vdc2 for all values of firing angle | |
| 534. |
In a 3 phase bridge inverter, the gating signals for the three phases have a phase difference of |
| A. | 120° |
| B. | 60° |
| C. | 240° |
| D. | any of the above |
| Answer» B. 60¬∞ | |
| 535. |
An SCR is triggered at 40° in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80°, the average anode current is likely to be |
| A. | 50 A |
| B. | 25 A |
| C. | less than 50 A but more than 25 A |
| D. | less than 25 A |
| Answer» D. less than 25 A | |
| 536. |
A dc circuit breaker must use |
| A. | natural commutation |
| B. | forced commutation |
| C. | both natural and forced commutation |
| D. | either natural or forced commutation |
| Answer» C. both natural and forced commutation | |
| 537. |
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. | 2002 V |
| Answer» D. 2002 V | |
| 538. |
The amount of dielectric heating is inversely proportional to frequency. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 539. |
A chopper cannot be line commutated. |
| A. | 1 |
| B. | |
| C. | DC circuits only |
| D. | AC circuits only |
| Answer» B. | |
| 540. |
A semiconverter feeding an RLE load operates in |
| A. | first quadrant only |
| B. | first and second quadrants |
| C. | first and fourth quadrants |
| D. | first and third quadrants |
| Answer» B. first and second quadrants | |
| 541. |
Multiphase choppers are used in |
| A. | low power circuits |
| B. | high power circuit |
| C. | both low and high power circuits |
| D. | medium power circuits |
| Answer» C. both low and high power circuits | |
| 542. |
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 | |
| 543. |
In a 3 phase fully controlled converter the firing frequency is |
| A. | 3 times the line frequency |
| B. | 6 times the line frequency |
| C. | 9 times the line frequency |
| D. | 12 times the line frequency |
| Answer» C. 9 times the line frequency | |
| 544. |
Assertion (A): SUS is a PUT and avalanche diode connected between gate and cathodeReason (R): SBS has two SUS inbuilt together and connected in anti-parallel |
| 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 | |
| 545. |
A two winding transformer is feeding a single phase half wave rectifier circuit. The load is purely resistive. The rms value of transformer secondary current is Is and rms value of load current in Irms. Then |
| A. | Is = Irms irrespective of the value of firing angle |
| B. | Is = 0.5 Irms irrespective of the value of firing angle |
| C. | Is = Irms if firing angle is less than 30° |
| D. | Is = Irms if firing angle is more than 30° |
| Answer» B. Is = 0.5 Irms irrespective of the value of firing angle | |
| 546. |
In the below figure the average load current is 15 A. The rms value of transformer secondary current is |
| A. | 15 A |
| B. | 10.61 A |
| C. | 7.5 A |
| D. | 14.14 A |
| Answer» C. 7.5 A | |
| 547. |
In a semi converter feeding a resistive load |
| A. | the waveshapes of output voltage and output current are exactly similar |
| B. | the waveshapes of output voltage and output current can not be similar |
| C. | the waveshapes of output voltage and output current are similar only for low values of firing angle |
| D. | the waveshapes of output voltage and output current may be similar or dissimilar |
| Answer» B. the waveshapes of output voltage and output current can not be similar | |
| 548. |
The number of leads in an SCR are : |
| A. | 2 |
| B. | 3 |
| C. | 4 |
| D. | 5 |
| Answer» C. 4 | |
| 549. |
In a dual converter both converters work as rectifiers. |
| A. | 1 |
| B. | |
| C. | short duration pulses |
| D. | long duration pulses |
| Answer» C. short duration pulses | |
| 550. |
The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by |
| A. | forward characteristics of thyristors |
| B. | reverse recovery characteristics of thyristors |
| C. | both forward and reverse recovery characteristics of thyristors |
| D. | none of the above |
| Answer» C. both forward and reverse recovery characteristics of thyristors | |