# Floyd: MCQ in Thyristors

(Last Updated On: December 6, 2019) This is the Multiple Choice Questions in Thyristors from the book Electronic Devices – Electron Flow Version and Conventional Current Version 8th Edition by Thomas L. Floyd. If you are looking for a reviewer in Electronics Engineering this will definitely help. I can assure you that this will be a great help in reviewing the book in preparation for your Board Exam. Make sure to familiarize each and every questions to increase the chance of passing the ECE Board Exam.

If you are looking for the Self-test in Floyd’s Electronic Devices proceed to

#### Practice Exam Test Questions

Choose the letter of the best answer in each questions.

1. Refer to Figure 11-1. Identify the triac. Figure 11-1

A a

B. b

C. c

D. d

E. e

Solution:

2. Refer to Figure 11-1. Which symbol represents a UJT?

A a

B. b

C. c

D. d

E. e

Solution:

3. Refer to Figure 11-1. Identify the symbol for an SCS.

A a

B. b

C. c

D. d

E. e

Solution:

4. Refer to Figure 11-1. Identify the diac symbol.

A a

B. b

C. c

D. d

E. e

Solution:

5. Refer to Figure 11-1. What is the correct symbol for an SCR?

A. a

B. b

C. c

D. d

E. e

Solution:

6. You have a need to use a device to trigger an SCR. A good one to use might be

A. an SCS.

B. a UJT.

C. a 4-layer diode.

D. a PUT.

Solution:

7. Which of the following devices might best be used to control an electric motor?

A. an SCS

B. a PUT

C. an SCR

D. a diac

Solution:

8. An SCR acts to control the speed of an electric motor by ______ the ______ of the pulse delivered to the motor.

A. varying, width

B. increasing, amplitude

C. decreasing, gate width

D. none of these

Solution:

9. You need to design a relaxation oscillator circuit. The most likely device to use might be

A. an SCR.

B. a UJT.

C. a triac.

D. a 4-layer diode.

Solution:

10. You need a very efficient thyristor to control the speed of an AC fan motor. A good device to use would be

A. a 4-layer diode.

B. a PUT.

C. a triac.

D. a BJT.

Solution:

11. You have the schematic diagram of several types of circuits. Which of these circuits most likely uses a triac?

A. an oscillator

B. an ac motor control

C. a programmable oscillator

D. an amplifier

Solution:

12. You have a light-dimmer circuit using an SCR. In testing the circuit, you find that IG = 0 mA and the light is still on. You conclude that the trouble might be one of the following:

A. the SCR is open.

B. the switch is faulty.

C. the gate circuit is shorted.

D. this is normal; nothing is wrong.

Solution:

13. Your boss has asked you to recommend a thyristor that will enable you to turn it on with a pulse and also turn it off with a pulse. Which of the following should you recommend?

A. an SCR

B. an SCS

C. a PUT

D. a triac

Solution:

14. How many semiconductor layers are thyristors constructed with?

A. 2

B. 3

C. 4

D. 5

Solution:

15. The SCR can be triggered on by a pulse at the

A. gate.

B. anode.

C. cathode.

D. none of the above

Solution:

16. An application of a(n) _____ is in a lighting system for power interruptions.

A. SCR

B. SCS

C. diac

D. triac

Solution:

17. The _____ can conduct current in either direction and is turned on when a breakover voltage is exceeded.

A. SCR

B. diac

C. SCS

D. triac

Solution:

18. The _____ is like a diac with a gate terminal.

A. triac

B. SCR

C. SCS

D. none of the above

Solution:

19. The silicon-controlled switch (SCS) is similar in construction to the

A. triac.

B. diac.

C. SCR.

D. 4-layer diode.

Solution:

20. The ______ can be externally programmed to turn on at a desired anode-to-gate voltage level.

A. UJT

B. PUT

C. SCR

D. SCS

Solution:

21. Identify the symbol: A. SCS

B. PUT

C. LASCR

D. diac

Solution:

22. Identify the symbol: A. triac

B. PUT

C. LASCR

D. SCR

Solution:

#### TRUE/FALSE

1. Thyristors are 4-layer semiconductor devices.

A. True

B. False

Solution:

2. The SCR is a device that can be triggered off by a pulse applied to the gate.

A. True

B. False

Solution:

3. The diac can conduct current in either direction and is turned on when a breakover voltage is exceeded.

A. True

B. False

Solution:

4. The anode-to-gate voltage can be used to turn the PUT on or off.

A. True

B. False

Solution:

5. The triac can be turned on or off by a pulse at the gate.

A. True

B. False

Solution:

6. The SUS is also known as a Shockley diode.

A. True

B. False

Solution:

7. The SCS is turned on with the cathode gate, and turned off with the anode gate.

A. True

B. False

Solution:

8. In an SCR-based half-wave phase-control circuit, a diode is connected in series with the anode.

A. True

B. False

Solution:

9. UJTs can only be used to trigger triacs, not SCRs.

A. True

B. False

Solution:

10. The triac is similar to an SCR, but it provides conduction for both halves of the ac wave.

A. True

B. False

Solution:

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