Silicon Controlled Rectifier - SCR MCQs Quiz Multiple Choice Questions & Answers

1. An SCR combines the features of …………..

1. None of the above
2. A rectifier and resistance
3. A rectifier and transistor
4. A rectifier and capacitor

2. If the gate voltage of an SCR is removed, then the

1. cathode current increases
2. anode current decreases
3. anode current does not decrease at all
4. anode current increases

3. An SCR is turned off when …………..

1. None of the above
2. Anode current is reduced to zero
3. Gate voltage is reduced to zero
4. Gate is reverse biased

4. An SCR is turned off when

1. None of the above
2. Anode current is reduced to zero
3. Gate voltage is reduced to zero
4. Gate is reverse biased

5. An SCR can be used

1. all of these
2. as static conductor
3. for power control
4. for speed control of dc shunt motor

6. In the normal operation of an SCR, anode is …………… w.r.t. cathode

1. None of the above
2. At zero potential
3. Negative
4. Positive

7. With gate open, the maximum anode current at which SCR is turned off from ON condition is called

1. latching current
2. breakdown voltage
3. peak reverse voltage
4. holding current

8. The normal way to turn on a SCR is by ……………..

1. None of the above
2. Breakover voltage
3. Appropriate anode current
4. Appropriate gate current

9. The control element of an SCR is ………….

1. Gate
2. Cathode
3. Anode
4. Anode supply

10. When SCR starts conducting, which loses all control?

1. None of the above
2. Cathode
3. Gate
4. Anode

11. An SCR has three terminals viz ……………

1. None of the above
2. Cathode, anode, gate
3. Anode, cathode, grid
4. Anode, cathode, drain

12. In an SCR circuit, the angle of conduction can be changed by ……….

1. None of the above
2. Changing anode voltage
3. Changing gate voltage
4. Reverse biasing the gate

13. In an SCR circuit, the angle of conduction can be changed by

1. None of the above
2. Changing anode voltage
3. Changing gate voltage
4. Reverse biasing the gate

14. In an SCR circuit the supply voltage is generally ……….. that of breakover voltage

1. None of the above
2. Equal to
3. Less than
4. Greater than

15. In an SCR circuit, the supply voltage is generally ......... that of breakover voltage

1. None of the above
2. Equal to
3. Less than
4. Greater than

16. When SCR is OFF, the current in the circuit is …………….

1. None of the above
2. Exactly zero
3. Small leakage current
4. Large leakage current

17. When SCR starts conducting, then …………… loses all control

1. None of the above
2. Gate
3. Cathode
4. Anode

18. An SCR is made of ………….

1. None of the above
2. Germanium
3. Silicon
4. Carbon

19. If gate current is increased, then anode-cathode voltage at which SCR closes …………….

1. None of the above
2. Is decreased
3. Is increased
4. Remains the same

20. If gate current is increased, then anode-cathode voltage at which SCR turns ON

1. none of the above
2. is decreased
3. is increased
4. remains the same

21. An SCR is made of silicon and not germanium because silicon ………

1. Is tetravalent
2. Is inexpensive
3. Is mechanically strong
4. Has small leakage current

22. In normal operation of an SCR, gate is ………..w.r.t. cathode

1. None of the above
2. Positive
3. Negative
4. At zero potential

23. An SCR can exercise control over ………. of a.c. supply

1. Positive or negative half-cycles
2. Positive half-cycles only
3. Negative half-cycles only
4. Both positive and negative half-cycles

24. In AC supply, an SCR can exercise control over

1. Positive or negative half-cycles
2. Positive half-cycles only
3. Negative half-cycles only
4. Both positive and negative half-cycles

25. A single phase ac - dc converter is also known as

1. regulator
2. rectifier
3. inverter
4. chopper

26. An SCR is turned off by …………….

1. None of the above
2. Reducing anode voltage to zero
3. Reducing gate voltage to zero
4. Reverse biasing the gate

27. If firing angle in an SCR circuit is increased, the output …………

1. None of the above
2. Remains the same
3. Is increased
4. Is decreased

28. If firing angle is increased, then the output of an SCR

1. None of the above
2. Remains the same
3. Is increased
4. Is decreased

29. An SCR is sometimes called …………

1. Thyristor
2. Triac
3. Diac
4. Unijunction transistor

30. An SCR is a solid state equivalent of …………….

1. Tetrode
2. Triode
3. Pentode
4. Gas-filled triode

31. An SCR has …………….. pn junctions

1. None of the above
2. Two
3. Three
4. Four

32. An SCR has ………….. semiconductor layers

1. None of the above
2. Two
3. Three
4. Four

33. We can control a.c. power in a load by connecting …………

1. None of the above
2. Two SCRs in series
3. Two SCRs in parallel
4. Two SCRs in parallel opposition

34. AC power in a load can be controlled by connecting

1. None of the above
2. Two SCRs in series
3. Two SCRs in parallel
4. Two SCRs in parallel opposition

35. An SCR behaves as a ……………. switch

1. None of the above
2. Unidirectional
3. Bidirectional
4. Mechanical

36. An SCR is a ……………….. triggered device

1. None of the above
2. Voltage
3. Current
4. Voltage as well as current

37. An SCR is a ...... triggered device

1. None of the above
2. Voltage
3. Current
4. Voltage as well as current

38. When an SCR is turned on, the voltage across it is about ……….

1. 1 V
2. Zero
3. 10 V
4. 1 V

39. When an SCR is turned on, the voltage across it is about ..........

1. 1V
2. zero
3. 10 V
4. 0.1 V