MCQOPTIONS
Saved Bookmarks
MCQOPTIONS
This section includes 657 Mcqs, each offering curated multiple-choice questions to sharpen your Testing Subject knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
If 4 quadrant operation is required we need |
| A. | dual converter |
| B. | full converter |
| C. | semi converter |
| D. | none of the above |
| Answer» B. full converter | |
| 2. |
A LASCR has |
| A. | 4 semiconductor layers and 3 junctions |
| B. | 3 semiconductor layers and 2 junctions |
| C. | 2 semiconductor layers and 2 junctions |
| D. | any of these depending on the rating |
| Answer» B. 3 semiconductor layers and 2 junctions | |
| 3. |
In a controlled rectifier a freewheeling diode is necessary if the load is |
| A. | capacitive |
| B. | any of the above |
| C. | 1 |
| D. | |
| Answer» B. any of the above | |
| 4. |
On load tap changer using thyristors can have a maximum of two taps. |
| A. | 1 |
| B. | |
| C. | Both A and R are correct and R is correct explanation of A |
| D. | Both A and R correct but R is not correct explanation of A |
| Answer» C. Both A and R are correct and R is correct explanation of A | |
| 5. |
In a single phase full wave regulator feeding R-L load, short gate pulse are not suitable. |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» B. | |
| 6. |
Which chopper circuit operates in all the 4 quadrants? |
| A. | A |
| B. | C |
| C. | D |
| D. | E |
| Answer» E. | |
| 7. |
An SCR has a turn on time of 4 μs. The gate pulse should have a duration of about |
| A. | 2 μs |
| B. | 5 μs |
| C. | 20 μs |
| D. | 50 μs |
| Answer» C. 20 Œºs | |
| 8. |
The characteristics of which device has peak point and valley point |
| A. | SCR |
| B. | PUT |
| C. | SCS |
| D. | Shockley diode |
| Answer» C. SCS | |
| 9. |
In figure, thyristor Th is in off state. When thyristor is turned on, the peak thyristor current can be |
| A. | 0.20833333333333 |
| B. | 0.41666666666667 |
| C. | 15 A |
| D. | 20 A |
| Answer» D. 20 A | |
| 10. |
In controlled heating circuits, thyristors act as |
| A. | ac regulator |
| B. | chopper |
| C. | are always similar |
| D. | can never be similar |
| Answer» D. can never be similar | |
| 11. |
Assertion (A): McMurray Bredford half bridge inverter uses complementary commutationReason (R): Three phase inverter can have two modes of operation. |
| 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 | |
| 12. |
In a parallel inverter the turn off time tq of thyristor and values of commutating elements L and C are related as |
| A. | tq = LC |
| B. | tq = LC |
| C. | by applying a positive signal to gate |
| D. | by applying a negative signal to gate |
| Answer» D. by applying a negative signal to gate | |
| 13. |
The gate lead, in a thyristor is welded to : |
| A. | p layer to which anode is connected |
| B. | n layer nearest to the anode terminal |
| C. | p layer nearest to the cathode terminal |
| D. | outside n layer |
| Answer» C. p layer nearest to the cathode terminal | |
| 14. |
In the circuit of figure, the waveshape of load current when thyristor conducting is |
| A. | decreasing exponentially |
| B. | either (b) or (c) |
| C. | only in positive half cycle |
| D. | both in positive and negative half cycles |
| Answer» C. only in positive half cycle | |
| 15. |
A 3 phase dual converter consists of |
| A. | two 3 phase semiconverters connected in parallel |
| B. | two 3 phase semiconverters connected in antiparallel |
| C. | two 3 phase full converters connected in antiparallel |
| D. | two 3 phase full converters connected in parallel |
| Answer» D. two 3 phase full converters connected in parallel | |
| 16. |
The application of gate signal decreases the break over voltage of on SCR. |
| A. | 1 |
| B. | |
| C. | low and leading |
| D. | low and lagging |
| Answer» B. | |
| 17. |
In a 3 phase full wave regulator feeding a star connected resistance load, firing angle is 75°. Then the number of thyristors conducting at one time is |
| A. | 3 |
| B. | 4 |
| C. | SUS |
| D. | SBS |
| Answer» C. SUS | |
| 18. |
A TRIAC is equivalent to |
| A. | two thyristors in series |
| B. | two thyristors in parallel |
| C. | one thyristor and one diode |
| D. | one thyristor and one transistor |
| Answer» C. one thyristor and one diode | |
| 19. |
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 | |
| 20. |
In a single phase half wave converter feeding resistive load and full wave converter (M - 2 connection) feeding a resistive load the circuit conditions are similar. The firing angle is a. Then the waveshapes of voltages across thyristors |
| A. | are similar |
| B. | are not similar |
| C. | may be similar or dissimilar |
| D. | are similar only for some values of a |
| Answer» B. are not similar | |
| 21. |
The condition for underdamped oscillations in a series RLC circuit is |
| A. | |
| B. | |
| Answer» C. | |
| 22. |
A step down cycloconverter has an input frequency f. If it uses natural commutation, the output frequency |
| A. | must be an even sub-multiple of input frequency |
| B. | must be an odd sub-multiple of input frequency |
| C. | 2Ir |
| D. | 2 Ir |
| Answer» B. must be an odd sub-multiple of input frequency | |
| 23. |
A dc chopper is feeding an RLE load. The condition for maximum ripple is |
| A. | a = 1 |
| B. | a = 0.8 |
| C. | a = 0.5 |
| D. | a < 0.5 |
| Answer» B. a = 0.8 | |
| 24. |
Which of these triggering methods for series connected SCRs use LASCR in the gate circuit? |
| A. | Resistance triggering |
| B. | Simultaneous triggering |
| C. | Sequential triggering |
| D. | Optical triggering |
| Answer» E. | |
| 25. |
In Jone chopper, the commutating element |
| A. | is a capacitor |
| B. | is a capacitor and an inductor |
| C. | is a capacitor and an auto transformer |
| D. | none of the above |
| Answer» D. none of the above | |
| 26. |
Assertion (A): A DIAC has four layers but only two terminals. Reason (R): A DIAC can conduct in both directions. |
| A. | A is correct but R is wrong |
| B. | A is wrong but R is correct |
| C. | firing angle is less than 60° |
| D. | firing angle is less than 90° |
| Answer» C. firing angle is less than 60¬∞ | |
| 27. |
When a thyristor is conducting, the voltage drop across it is about |
| A. | 1 V |
| B. | 10 V |
| C. | 100 V |
| D. | 0.1 V |
| Answer» B. 10 V | |
| 28. |
The stud in a stud mounted SCR acts as |
| A. | anode |
| B. | cathode |
| C. | gate |
| D. | anode or cathode |
| Answer» B. cathode | |
| 29. |
A Shockley diode can be used |
| A. | in place of SCR |
| B. | as a trigger switch for SCR |
| C. | in place of UJT |
| D. | both in place of SCR and as a trigger switch for SCR |
| Answer» C. in place of UJT | |
| 30. |
A 3 phase series inverter has |
| A. | 12 thyristors |
| B. | 6 thyristors |
| C. | 3 thyristors |
| D. | 3 or 6 thyristors |
| Answer» C. 3 thyristors | |
| 31. |
A class D chopper |
| A. | can operate in either first or fourth quadrant |
| B. | can operate in all the quadrants |
| C. | UJT |
| D. | PUT |
| Answer» D. PUT | |
| 32. |
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 | |
| 33. |
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 | |
| 34. |
A class E chopper |
| A. | can operate in second quadrant only |
| B. | can operate in first or third quadrant |
| C. | can operate in all the four quadrants |
| D. | can operate in either second or third quadrant |
| Answer» D. can operate in either second or third quadrant | |
| 35. |
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 | |
| 36. |
A static excitation system uses |
| A. | transformer and thyristors |
| B. | transformer and ac exciter |
| C. | dc exciter and ac exciter |
| D. | transformer and dc exciter |
| Answer» B. transformer and ac exciter | |
| 37. |
A 750 A circuit uses thyristor of current rating 175 A. If derating is 25%, the number of thyristors in parallel is |
| A. | 6 |
| B. | 10 |
| C. | Both A and R are correct and R is correct explanation of A |
| D. | Both A and R correct but R is not correct explanation of A |
| Answer» D. Both A and R correct but R is not correct explanation of A | |
| 38. |
Which of these devices is used in relaxation oscillator? |
| A. | UJT |
| B. | SCR |
| C. | DIAC |
| D. | TRIAC |
| Answer» B. SCR | |
| 39. |
The waveshape of output voltage of half bridge inverter is |
| A. | sinusoidal |
| B. | square |
| C. | triangular |
| D. | either (a) or (b) |
| Answer» C. triangular | |
| 40. |
A silicon controlled switch has : |
| A. | 2 leads |
| B. | 3 leads |
| C. | 4 leads |
| D. | 5 leads |
| Answer» D. 5 leads | |
| 41. |
For a single phase half wave converter feeding a resistive load, the firing angle a. The waveshape in below figure is for |
| A. | output voltage |
| B. | input voltage |
| C. | voltage drop across thyristor |
| D. | none of the above |
| Answer» E. | |
| 42. |
Assertion (A): The output voltage of an inverter can be controlled by PWM techniqueReason (R): In a current source inverter the input current is constant. |
| 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 | |
| 43. |
A string of series connected thyristors needs equalising circuit to |
| A. | ensure proper firing |
| B. | ensure proper current division |
| C. | ensure proper voltage division |
| D. | none of the above |
| Answer» D. none of the above | |
| 44. |
In a 3 phase full wave regulator feeding a star connected resistance load the input voltage is 400 V line to line. The firing angle is 160°. The line to line output voltage would be |
| A. | 400 V |
| B. | about 100 V |
| C. | about 20 V |
| D. | zero |
| Answer» E. | |
| 45. |
A chopper is a high efficiency circuit. |
| A. | 1 |
| B. | |
| C. | both these methods are based on entirely different principles |
| D. | in resonant commutation, the commutating elements carry load current but in self commutation, the commutating elements do not carry load current |
| Answer» B. | |
| 46. |
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 | |
| 47. |
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 | |
| 48. |
In a full bridge single phase inverter feeding RLC load |
| A. | one thyristor and one diode conduct simultaneously |
| B. | two thyristors conduct simultaneously |
| C. | two thyristors or two diodes conduct simultaneously |
| D. | four thyristors conduct simultaneously |
| Answer» D. four thyristors conduct simultaneously | |
| 49. |
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 a is |
| A. | 0 ≤ a ≤ p |
| B. | θ ≤ a ≤ p |
| C. | 0 ≤ a ≤ (p - θ) |
| D. | θ ≤ a ≤ (p + θ) |
| Answer» C. 0 ‚⧠a ‚⧠(p - Œ∏) | |
| 50. |
The leads in a TRIAC are denoted by |
| A. | T1, T2, anode |
| B. | T1, T2, T3 |
| C. | must be a sub-multiple of input frequency |
| D. | can be any frequency |
| Answer» C. must be a sub-multiple of input frequency | |