Online Questions and Answers Topic Outline
- MCQs in Introduction to pnpn and Other Devices | MCQs in Silicon-Controlled Rectifier (SCR) | MCQs in SCR Applications | MCQs in SCR Characteristics and Rating | MCQs in SCR Operation | MCQs in Silicon-Controlled Switch (SCS)| MCQs in Gate Turn-Off Switch (GTO) | MCQs in Light-Activated SCR (LASCR) | MCQs in Shockley Diode | MCQs in DIAC | MCQs in TRIAC | MCQs in Unijunction Transistor | MCQs in Phototransistors | MCQs in Opto-Isolators | MCQs in Programmable Unijunction Transistors (PUT)
Practice Exam Test Questions
Choose the letter of the best answer in each questions.
1. How many layers of semiconductor materials does a silicon-controlled rectifier (SCR) have?
- A. 2
- B. 3
- C. 4
- D. 5
2. Which of the following devices has (have) four layers of semiconductor materials?
- A. Silicon-controlled switch (SCS)
- B. Gate turn-off switch (GTO)
- C. Light-activated silicon-controlled rectifier (LASCR)
- D. All of the above
3. A thyristor is a _____-layer semiconductor material device.
- A. 2
- B. 3
- C. 4
- D. 5
4. Which of the following devices is unquestionably of the greatest interest today?
- A. SCR
- B. GTO
- C. LASCR
- D. SCS
5. What is the frequency range of application of SCRs?
- A. About 10 kHz
- B. About 50 kHz
- C. About 250 kHz
- D. About 1 mHz
6. Which one of the SCR terminals fires the SCR?
- A. Anode
- B. Cathode
- C. Gate
- D. All of the above
7. What is the typical value of the reverse resistance of SCRs?
- A. 1 Ω to 10 Ω
- B. 100 Ω to 1 kΩ
- C. 1 k Ω to 50 kΩ
- D. 100 kΩ or more
8. Which of the following transistors is an SCR composed of?
- A. npn, pnp
- B. npn, npn
- C. pnp, pnp
- D. None of the above
9. Which of the transistors of an SCR are conducting when the SCR is fired and is in the conduction mode?
- A. npn
- B. pnp
- C. Both npn and pnp
- D. Neither npn nor pnp
10. What is the range of the turn-on times in high-power SCR devices?
- A. 30 µs to 100 µs
- B. 10 µs to 25 µs
- C. 5 µs to 8 µs
- D. 1 µs to 5 µs
11. What is the typical range of turn-off times for SCRs?
- A. 5 µs to 30 µs
- B. 1 µs to 5 µs
- C. 0.1 µs to 1 µs
- D. 0.01 µs to 0.1 µs
12. This symbol is an example of a(n) _____.
- A. SCR
- B. SCS
- C. GTO
- D. DIAC
13. Which of the following parameters are usually provided by the manufacturer on the specification sheet for SCRs?
- A. Turn-on time (ton )
- B. Turn-off time (toff )
- C. Junction and case temperatures (tj and tc )
- D. All of the above
14. How many terminals does a silicon-controlled switch (SCS) device have?
- A. 2
- B. 3
- C. 4
- D. 5
15. What is the typical value of the triggering anode gate for SCS devices?
- A. 1.5 mA
- B. 150 A
- C. 15 A
- D. 1 A
16. Which of the following is (are) the advantages of the SCS over a corresponding SCR?
- A. Reduced turn-off time
- B. Increased control and triggering sensitivity
- C. More predictable firing situation
- D. All of the above
17. Which of the following areas is (are) applications of an SCS?
- A. Counters
- B. Pulse generators
- C. Voltage sensors
- D. All of the above
18. This symbol is an example of a(n)_____.
- A. SCR
- B. SCS
- C. GTO
- D. DIAC
19. For an SCS, a _____ pulse at the anode gate turns the device on, while a _____ pulse will turn it off.
- A. negative, positive
- B. positive, negative
20. An advantage of the SCR over the SCS is the reduced turn-off time.
- A. True
- B. False
21. Which of the following devices has the smallest turn-off time?
- A. SCR
- B. GTO
- C. SCS
- D. LASCR
22. Which of the following devices has nearly the same turn-on time as turn-off time?
- A. SCR
- B. GTO
- C. SCS
- D. LASCR
23. This symbol is an example of a(n) _____.
- A. SCR
- B. SCS
- C. GTO
- D. diac
24. What is the maximum current (rms) rating for commercially available LASCRs today?
- A. 3 A
- B. 15 A
- C. 20 A
- D. 25 A
25. How many terminals does a Shockley diode have?
- A. 5
- B. 4
- C. 3
- D. 2
26. This symbol is an example of a(n) _____.
- A. SCR
- B. SCS
- C. GTO
- D. DIAC
27. Which of the following devices does not have a cathode terminal?
- A. SCR
- B. SCS
- C. Triac
- D. Shockley diode
28. Today, the SCR is more widely used than the TRIAC.
- A. True
- B. False
29. Which of the following devices has a negative-resistance region in its characteristics curve?
- A. SCR
- B. SCS
- C. Unijunction transistor
- D. Phototransistor
30. What is the range of the variable resistor in the equivalent circuit of a unijunction transistor?
- A. 50 Ω to 5 kΩ
- B. 6 kΩ to 10 kΩ
- C. 5 Ω to 50 Ω
- D. 1 Ω to 5 Ω
31. This is an example of a high-isolation _____ gate.
- A. OR
- B. NOT
- C. AND
- D. NAND
32. The ISO-LIT Q1 16-pin Litronix opto-isolator DIP contains _____ opto-isolators.
- A. 4
- B. 8
- C. 12
- D. 6
33. How many terminals does a programmable unijunction transistor (PUT) have?
- A. 4
- B. 3
- C. 2
- D. 1
34. Determine RB1 for a silicon PUT if it is determined that h = 0.84, VP = 11.2 V, and RB2 = 5 kΩ.
- A. 12.65 kΩ
- B. 16.25 kΩ
- C. 20.00 kΩ
- D. 26.25 kΩ
FILL-IN-THE-BLANKS
1. The two-layer semiconductor diode has led to _____layer devices.
- A. three-
- B. four-
- C. five-
- D. All of the above
2. The four-layer devices with a control mechanism are commonly referred to as _____.
- A. thyristors
- B. transistors
- C. diodes
- D. None of the above
3. _____ are areas of application for SCRs.
- A. Relay controls
- B. Time-delay circuits
- C. Motor controls
- D. All of the above
4. SCRs have been designed to control powers as high as _____, with individual ratings as high as _____ at _____.
- A. 1800 MW, 10 A, 2000 V
- B. 1800 MW, 2000 A, 10 V
- C. 10 MW, 2000 A, 1800 V
- D. 2000 MW, 10 A, 1800 V
5. The _____ are the terminals of SCRs.
- A. anode and cathode
- B. anode, gate, and cathode
- C. base, anode, and cathode
- D. gate and anode
6. In the conduction region, the dynamic resistance of the SCR is typically _____ to _____.
- A. 0.01 Ω, 0.1 Ω
- B. 1 Ω, 10 Ω
- C. 50 Ω, 100 Ω
- D. 500 Ω, 10 kΩ
7. The SCRs have typical turn-on times of _____ in the regeneration action.
- A. 0.1 μs to 1 μs
- B. 0.1 ms to 1 ms
- C. 3 ms to 5 ms
- D. 5 ms to 9 ms
8. The method(s) for turning off an SCR is (are) categorized as _____.
- A. current interruption
- B. forced commutation
- C. both current interruption and forced commutation
- D. None of the above
9. At –65ºC the minimum current that will trigger the series of an SCR is _____, while at +150ºC only _____ is required.
- A. 20 mA, 100 mA
- B. 50 mA, 75 mA
- C. 75 mA, 50 mA
- D. 100 mA, 20 mA
10. In a half-wave variable-resistance phase control operation, the control cannot be extended past a ______ phase displacement.
- A. 45º
- B. 90º
- C. 135º
- D. 180º
11. The _____ are the terminals of an SCS.
- A. anode, anode gate, cathode gate, and cathode
- B. anode, cathode, cathode gate, and gate
- C. anode, anode gate, cathode, and gate
- D. anode, cathode, and gate
12. The _____ the anode gate current, the _____ the required anode-to-cathode voltage to turn the SCS device on.
- A. higher, higher
- B. lower, lower
- C. higher, lower
- D. None of the above
13. The anode gate connection can be used to turn the SCS device _____.
- A. on
- B. off
- C. neither on nor off
- D. either on or off
14. To turn on an SCS device, a _____ pulse must be applied to the anode gate terminal; to turn off the device, a _____ pulse is required.
- A. positive, positive
- B. negative, positive
- C. positive, negative
- D. negative, negative
15. In general, the triggering (turn-on) anode gate current is _____ the required cathode gate current.
- A. larger than
- B. the same as
- C. smaller than
- D. None of the above
16. A(n) _____ can be triggered in either direction.
- A. SCR
- B. Shockley diode
- C. diac
- D. SCS
17. _____ is (are) the element(s) of a unijunction transistor's equivalent circuit.
- A. One fixed resistor
- B. A variable resistor
- C. A diode
- D. All of the above
18. The current induced by photoelectric effects is the _____ current of the transistor.
- A. collector
- B. base
- C. emitter
- D. None of the above
19. _____ in light intensity corresponds with _____ in collector current.
- A. An increase, an increase
- B. An increase, a decrease
- C. A decrease, an increase
- D. None of the above
20. _____ is(are) example(s) of applications of phototransistors.
- A. Punch-card readers
- B. Lighting control (for example, on highways)
- C. Level indication
- D. All of the above
21. An opto-isolator contains _____.
- A. an infrared LED
- B. a photodetector
- C. both an infrared LED and a photodetector
- D. None of the above
22. The switching time of an opto-isolator _____ with increased current, while for many devices it is exactly the reverse.
- A. increases
- B. decreases
- C. remains the same
- D. None of the above
23. In a programmable unijunction transistor (PUT), the _____ can be controlled through a couple of resistors and the supply voltage.
- A. interbase resistance RBB
- B. intrinsic stand-off ratio
- C. emitter firing potential VP
- D. All of the above
24. The peak and valley currents of the PUT are typically _____ those of a similarly rated UJT.
- A. lower than
- B. the same as
- C. higher than
- D. None of the above
25. The minimum operating voltage of the UJT is typically _____ that of a similarly rated PUT.
- A. lower than
- B. the same as
- C. higher than
- D. None of the above
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