Online Questions and Answers Topic Outline
- MCQs in Introduction—Definitions and Amplifier Types
- MCQs in Series-Fed Class A Amplifier
- MCQs in Transformer-Coupled Class A Amplifier
- MCQs in Class B Amplifier Operation
- MCQs in Class B Amplifier Circuits
- MCQs in Amplifier Distortion
- MCQs in Power Transistor Heat Sinking
- MCQs in Class C and Class D Amplifiers
Practice Exam Test Questions
Choose the letter of the best answer in each questions.
1. Which of the following is (are) power amplifiers?
- a. Class A
- b. Class B or AB
- c. Class C or D
- d. All of the above
2. By how much does the output signal vary for a class AB power amplifier?
- a. 360º
- b. 180º
- c. Between 180º and 360º
- d. Less than 180º
3. Which type of power amplifier is biased for operation at less than 180º of the cycle?
- a. Class A
- b. Class B or AB
- c. Class C
- d. Class D
4. Which type of amplifier uses pulse (digital) signals in its operation?
- a. Class A
- b. Class B or AB
- c. Class C
- d. Class D
5. Which of the power amplifiers has the lowest overall efficiency?
- a. Class A
- b. Class B or AB
- c. Class C
- d. Class D
6. Which of the following describe(s) a power amplifier?
- a. It can handle large power.
- b. It can handle large current.
- c. It does not provide much voltage gain.
- d. All of the above
7. _____ amplifiers primarily provide sufficient power to an output load to drive a speaker from a few watts to tens of watts.
- a. Small-signal
- b. Power
- c. None of the above
8. The main features of a large-signal amplifier is the circuit's ______.
- a. power efficiency
- b. maximum power limitations
- c. impedance matching to the output device
- d. All of the above
9. This is an example of the output swing for a class _____ amplifier.
![clip_image002[33]](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFIWltyITK8fSjfZ7t6zsCZl_ffLl6Ukhyy5h1saBSyOstABLzH0naiv8l3Hjy4WgGQsV3G1HppxPbe8oanfi0sU-lWi0je-JFerYnQ0mnl663tC-My9XCvzWX64bntsQIAjVYzZw5qilZ/s1600-h/clip_image002%25255B33%25255D%25255B11%25255D.png "clip_image002[33]")
- a. A
- b. B
- c. AB
- d. C
- e. D
10. This is an example of the output swing for a class _____ amplifier.
![clip_image004[11]](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh24vxJm2P58qaJsfh2korjRU0ZdvFQWGuuQ8IC8tln46xgIJ7WITxjELRybkQ7aNCSjzBhpw5trg5oHtR4JFgq0xOakuVYoe-iO33mH7D4velx8VKghHgVOR1XcFlcCLcoyebFRtVYpRcm/s1600-h/clip_image004%25255B11%25255D%25255B10%25255D.png "clip_image004[11]")
- a. A
- b. B
- c. AB
- d. C
- e. D
11. Class AB operation is _____ operation.
- a. similar to class A
- b. similar to class B
- c. similar to class C
- d. None of the above
12. Which operation class is generally used in radio or communications?
- a. A
- b. B
- c. AB
- d. C
- e. D
13. Categorize the power efficiency of each class of amplifier, from worst to best.
- a. A, B, AB, D
- b. A, AB, D, B
- c. A, AB, B, D
14. What is the maximum efficiency of a class A circuit with a direct or series-fed load connection?
- a. 90%
- b. 78.5%
- c. 50%
- d. 25%
15. What is the ratio of the secondary voltage to the primary voltage with the turn ratio in the winding
- a. N2/N1
- b. (N1/N2)2
- c. (N1/N2)1/3
- d. N1 × N2
16. Calculate the effective resistance seen looking into the primary of a 20:1 transformer connected to an 8- Ω load.
- a. 3.2 kΩ
- b. 3.0 kΩ
- c. 2.8 kΩ
- d. 1.8 kΩ
17. What transformer turns ratio is required to match an 8-speaker load so that the effective load resistance seen at the primary is 12.8 k?
- a. 20:1
- b. 40:1
- c. 50:1
- d. 60:1
18. Calculate the efficiency of a transformer-coupled class A amplifier for a supply of 15 V and an output of V(p) = 10 V.
- a. 25%
- b. 33.3%
- c. 50%
- d. 78.5%
19. The maximum efficiency of a transformer-coupled class A amplifier is _____.
- a. 25%
- b. 50%
- c. 78.5%
- d. 63.6%
20. What is the maximum efficiency of a class B circuit?
- a. 90%
- b. 78.5%
- c. 50%
- d. 25%
21. How many transistors must be used in a class B power amplifier to obtain the output for the full cycle of the signal?
- a. 0
- b. 1
- c. 2
- d. 3
22. In class B operation, at what fraction of VCC should the level of VL(p) be to achieve the maximum power dissipated by the output transistor?
- a. 0.5
- b. 0.636
- c. 0.707
- d. 1
23. Class B operation is provided when the dc bias leaves the transistor biased just off, the transistor turning on when the ac signal is applied.
- a. True
- b. False
24. Calculate the efficiency of a class B amplifier for a supply voltage of VCC = 20 V with peak output voltage of VL(p) = 18 V. Assume RL = 16 Ω.
- a. 78.54%
- b. 75%
- c. 70.69%
- d. 50%
25. Which of the following is (are) the disadvantage(s) of a class B complementary-symmetry circuit?
- a. It needs two separate voltage sources.
- b. There is crossover distortion in the output signal.
- c. It does not provide exact switching of one transistor off and the other on at the zero-voltage condition.
- d. All of the above
26. Which of the push-pull amplifiers is presently the most popular form of the class B power amplifier?
- a. Quasi-complementary
- b. Transformer-coupled
- c. Complementary-symmetry
- d. None of the above
27. nMOS and pMOS transistors can be used for class B.
- a. True
- b. False
28. Calculate the harmonic distortion component for an output signal having fundamental amplitude of 3 V and a second harmonic amplitude of 0.25 V.
- a. 3.83%
- b. 38.3%
- c. 83.3%
- d. 8.33%
29. Which of the following instruments displays the harmonics of a distorted signal?
- a. Digital multimeter
- b. Spectrum analyzer
- c. Oscilloscope
- d. Wave analyzer
30. Which of the following instruments allows more precise measurement of the harmonic components of a distorted signal?
- a. Digital multimeter
- b. Spectrum analyzer
- c. Oscilloscope
- d. Wave analyzer
31. What is the maximum temperature rating for silicon power transistors?
- a. 50º to 80º
- b. 100º to 110º
- c. 150º to 200º
- d. 250º to 300º
32. Which of the power amplifiers is not intended primarily for large-signal or power amplification?
- a. Class A
- b. Class B or AB
- c. Class C
- d. Class D
33. Determine what maximum dissipation will be allowed for a 70-W silicon transistor (rated at 25ºC) if derating is required above 25ºC by a derating factor of 0.6 W/ºC at a case temperature of 100º.
- a. 25 W
- b. 30 W
- c. 35 W
- d. 40 W
34. A silicon power transistor is operated with a heat sink (θSA = 1.5ºC/W). The transistor, rated at 150 W (25ºC), has θJC = 0.5º C/W, and the mounting insulation has θCS = 0.6 ºC/W. What is the maximum power that can be dissipated if the ambient temperature is 50ºC and TJmax = 200 ºC?
- a. 61.5 W
- b. 60.0 W
- c. 57.7 W
- d. 55.5 W
35. Which of the following transistors has been quite popular as the driver device for class D amplification?
- a. BJT
- b. FET
- c.UJT
- d. MOSFET
FILL-IN-THE-BLANKS
1. Power amplifiers primarily provide sufficient power to an output load, typically from _____ to _____.
- A. a few kW, tens of kW
- B. 500 W, 1 kW
- C. 100 W, 500 W
- D. a few W, tens of W
2. The main feature(s) of a large-signal amplifier is (are) the _____.
- A. circuit's power efficiency
- B. maximum amount of power that the circuit is capable of handling
- C. impedance matching to the output
- D. All of the above
3. In _____ power amplifiers, the output signal varies for a full 360º of the cycle.
- A. class A
- B. class B or AB
- C. class C
- D. class D
4. In class B power amplifiers, the output signal varies for _____ of the cycle.
- A. 360º
- B. 180º
- C. between 180º and 360º
- D. less than 180º
5. _____ amplifiers have the highest overall efficiency.
- A. Class A
- B. Class B or AB
- C. Class C
- D. Class D
6. Class D operation can achieve power efficiency of over _____.
- A. 90%
- B. 78.5%
- C. 50%
- D. 25%
7. The beta of a power transistor is generally _____.
- A. more than 200
- B. 100 to 200
- C. less than 100
- D. 0
8. A form of class A amplifier having maximum efficiency of _____ uses a transformer to couple the output signal to the load.
- A. 90%
- B. 78.5%
- C. 50%
- D. 25%
9. The reflected impedance seen from one side of the transformer to the other side is _____.
- A. N1/N2
- B. (N1/N2)2
- C. (N1/N2)1/3
- D. N1× N2
10. In a class A transformer-coupled power amplifier, _____ winding resistance of the transformer determine(s) the dc load line for the circuit.
- A. the ac
- B. the dc
- C. both the ac and dc
- D. neither the ac nor dc
11. The slope of the ac load line in the class A transformer-coupled transistor is _____.
- A. –1/RL (load resistor)
- B. 1/(a2RL)
- C. –1/(a2RL)
- D. 1/RL
12. The amount of power dissipated by the transistor is the _____ of that drawn from the dc supply (set by the bias point) and the amount delivered to the ac load.
- A. product
- B. difference
- C. average
13. A class A amplifier dissipates _____ power when the load is drawing maximum power from the circuit.
- A. the least
- B. about the same
- C. the most
- D. None of the above
14. In a class A transformer-coupled amplifier, the _____ the value of VCEmax and the _____ the value of VCEmin, the _____ the efficiency to (from) the theoretical limit of 50%.
- A. larger, smaller, farther
- B. larger, smaller, closer
- C. smaller, larger, closer
- D. None of the above
15. In class B operation, the current drawn from a single power supply has the form of _____ rectified signal.
- A. a full-wave
- B. a half-wave
- C. both a full-wave and a half-wave
- D. None of the above
16. The highest efficiency is obtained in class B operation when the level of VL(p) is equal to _____.
- A. 0.25VCC
- B. 0.50VCC
- C. VCC
- D. 2VCC
17. _____ transistors can be used to build a class B amplifier.
- A. npn and pnp
- B. nMOS and pMOS
- C. Both npn and pnp or nMOS and pMOS
- D. None of the above
18. The complementary Darlington-connected transistor for a class B amplifier provides _____ output current and _____ output resistance.
- A. higher, higher
- B. higher, lower
- C. lower, lower
- D. lower, higher
19. The fundamental component is typically _____ any harmonic component.
- A. larger than
- B. the same as
- C. smaller than
- D. None of the above
20. In Fourier technique, any periodic distorted waveform can be represented by _____ the fundamental and all harmonic components.
- A. multiplying
- B. subtracting
- C. dividing
- D. adding
21. Improvement in production techniques of power transistors have _____.
- A. produced higher power ratings in small-sized packaging cases
- B. increased the maximum transistor breakdown voltage
- C. provided faster-switching power transistors
- D. All of the above
22. The greater the power handled by the power transistor, _____ the case temperature.
- A. the higher
- B. the lower
- C. there is no change in
- D. None of the above
23. The _____ has the hottest temperature in a power transistor.
- A. heat sink
- B. case
- C. junction
- D. None of the above
24. A heat sink provides _____ thermal resistance between case and air.
- A. a high
- B. a low
- C. the same
- D. None of the above
25. A _____ power amplifier is limited to use at one fixed frequency.
- A. class A
- B. class B or AB
- C. class C
- D. class D
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