### Online Questions and Answers Topic Outline

- MCQs in Feedback Concepts | MCQs in Feedback Connection Types | MCQs in Practical Feedback Circuits | MCQs in Feedback Amplifier | MCQs in Oscillator Operation | MCQs in Phase-Shift Oscillator | MCQs in Wien Bridge Oscillator | MCQs in Tuned Oscillator Circuit | MCQs in Crystal Oscillator | MCQs in Unijunction Oscillator

### Practice Exam Test Questions

**Choose the letter of the best answer in each questions.**

1. Which of the following improvements is (are) a result of the negative feedback in a circuit?

- A. Higher input impedance
- B. Better stabilized voltage gain
- C. Improved frequency response
- D. All of the above

2. Which of the following improvements is (are) a result of the negative feedback in a circuit?

- A. Lower output impedance
- B. Reduced noise
- C. More linear operation
- D. All of the above

3. Which of the following is (are) feedback?

- A. Voltage-series
- B. Voltage-shunt
- C. Current-series
- D. All of the above

4. What is the ratio of the input impedance with series feedback to that without feedback?

- A. 1 + Î²A
- B. Î²A
- C. Î²
- D. 1

5. What is the ratio of the output impedance with series feedback to that without feedback?

- A. 1
- B. 1 + Î²A
- C. Î²A
- D. A

6. The frequency distortion arising because of varying amplifier gain with frequency is considerably reduced in a negative-voltage feedback amplifier circuit.

- A. True
- B. False

7. Determine the voltage gain with feedback for a voltage-series feedback having A = –100, R_{1} = 15 kâ„¦, Ro = 20 kâ„¦, and a feedback of Î² = –0.25.

- A. 3.85
- B. –3.85
- C. –9.09
- D. 9.09

8. Determine the input impedance with feedback for a voltage-series feedback having A = –100, R_{1} = 15 kâ„¦, Ro = 20 kâ„¦, and a feedback of Î² = –0.25.

- A. 110 kâ„¦
- B. 290 kâ„¦
- C. 390 kâ„¦
- D. 510 kâ„¦

9. Determine the output impedance with feedback for a voltage-series feedback having A = –100, R_{1} = 15 kâ„¦, Ro = 20 kâ„¦, and a feedback of Î² = –0.25.

- A. 0.2 kâ„¦
- B. 392.16 kâ„¦
- C. 1.82 kâ„¦
- D. 769.23 â„¦

10. An amplifier with a gain of –500 and a feedback of Î² = –0.1 has a gain change of 15% due to temperature. Calculate the change in gain of the feedback amplifier.

- A. 0.2%
- B. 0.3%
- C. 0.4%
- D. 0.5%

11. Referring to this figure, calculate the amplification gain with feedback for the following circuit values: R_{1} = 80 kâ„¦, R_{2} = 20 kâ„¦, Ro = 10 kâ„¦, R_{D} = 61 kâ„¦, and gm = 4000 Î¼S.

- A. –4.36
- B. –4.25
- C. –6.35
- D. –20.85

12. Referring to this figure, calculate the amplification gain where the op-amp gain (A) is 200,000, R_{1 }= 1.5 kâ„¦, and R_{2} = 400 â„¦.

- A. 4.25
- B. 4.50
- C. 4.75
- D. 5.00

13. Referring to this figure, calculate the voltage gain with feedback A_{vf}.

- A. –4.85
- B. –4.20
- C. –4.17
- D. –4.00

14. Referring to this figure, calculate the voltage gain without feedback for the following circuit values: R_{D} = 4 kâ„¦, R_{S} = 1 kâ„¦, R_{F} = 15 kâ„¦, and gm = 5000 Î¼S.

- A. –20.0
- B. –21.5
- C. –23.5
- D. –25.5

15. Referring to this figure, calculate the voltage gain with the feedback for the following circuit values: R_{D} = 4 kâ„¦, R_{S} = 1 kâ„¦, R_{F} = 15 kâ„¦, and gm = 5000 Î¼S.

- A. –11.2
- B. –8.57
- C. –6.75
- D. –3.25

16. Which of the following is (are) the determining factor(s) of the stability of a feedback amplifier?

- A. A
- B. Phase shift between input and output signals
- C. Both A and the phase shift between input and output signals
- D. None of the above

17. At what phase shift is the magnitude of Î²A at its maximum in the Nyquist plot?

- A. 90Âº
- B. 180Âº
- C. 270Âº
- D. 0Âº

18. At what phase shift is the magnitude of Î²A at its minimum in the Nyquist plot?

- A. 90Âº
- B. 180Âº
- C. 270Âº
- D. 0Âº

19. The Nyquist plot combines the two Bode plots of gain versus frequency and phase shift versus frequency on a single plot.

- A. True
- B. False

20. The amplifier is unstable if the Nyquist curve plotted encloses (encircles) the –1 point, and it is stable otherwise.

- A. True
- B. False

21. Which of the following is required for oscillation?

- A. Î²A > 1
- B. The phase shift around the feedback network must be 180Âº.
- C. Both Î²A > 1 and the phase shift around the feedback network must be 180Âº.
- D. None of the above

22. An input signal is needed for an oscillator to start.

- A. True
- B. False

23. Only the condition Î²A = _____ must be satisfied for self-sustained oscillations to result.

- A. 0
- B. –1
- C. 1
- D. None of the above

24. Given gm = 5000 ÂµS, r_{d} = 40 kâ„¦, R = 10 kâ„¦, and A = 35. Determine the value of R_{D} for oscillator operation at 1 kHz.

- A. 8.05 kâ„¦
- B. 8.48 kâ„¦
- C. 10.8 kâ„¦
- D. 12.3 kâ„¦

25. In the IC phase-shift oscillator, what should the ratio of feedback resistor R_{f} to R_{1} be?

- A. Zero
- B. Greater than –29
- C. Less than 29
- D. Any value

26. This circuit is a _____ oscillator.

- A. phase-shift
- B. Wien bridge
- C. Colpitts
- D. Hartley

27. For a phase-shift oscillator, the gain of the amplifier stage must be greater than _____.

- A. 19
- B. 29
- C. 30
- D. 1

28. In the Wien bridge oscillator, which of the following is (are) frequency-determining components?

- A. R
_{1}and R_{2} - B. C
_{1}and C_{2} - C. R
_{1}, R_{2}, C_{1}, and C_{2} - D. None of the above

29. Calculate the resonant frequency of this oscillator.

- A. 1560.34 Hz
- B. 3120.70 Hz
- C. 4681.07 Hz
- D. 6241.37 Hz

30. Calculate the resonant frequency of this Wien bridge oscillator if R_{1} = 25 kâ„¦, R_{2} = 40 kâ„¦, C_{1} = 0.001 ÂµF, and C_{2} = 0.002 ÂµF.

- A. 1560.3 Hz
- B. 1779.4 Hz
- C. 3120.7 Hz
- D. 3558.8 Hz

31. Calculate the value of C_{1} = C_{2} for the Wien bridge oscillator to operate at a frequency of 20 kHz. Assume R_{1} = R_{2} = 50 kâ„¦ and R_{3} = 3R_{4} = 600 â„¦?

- A. 1.59 pF
- B. 15.9 pF
- C. 159 pF
- D. 1.59 nF

32. This circuit is a _____ oscillator.

- A. phase-shift
- B. Wien bridge
- C. Colpitts
- D. Hartley

33. Which of the following oscillators is (are) tuned oscillators?

- A. Colpitts
- B. Hartley
- C. Crystal
- D. All of the above

34. This circuit is a _____ oscillator.

- A. phase-shift
- B. Wien bridge
- C. Colpitts
- D. Hartley

35. What is the typical value of quality factor for crystal oscillators?

- A. 20,000
- B. 1000
- C. 100
- D. 10

#### FILL-IN-THE-BLANKS

1. Negative feedback results in _____.

- A. decreased voltage gain
- B increased voltage gain
- C. oscillation in the circuit
- D. None of the above

2. Positive feedback results in _____.

- A. decreased voltage gain
- B. increased voltage gain
- C. oscillation in the circuit
- D. None of the above

3. Series-feedback connections tend to _____ the input resistance. Shunt feedback connections tend to _____ the input resistance.

- A. decrease, increase
- B. increase, decrease
- C. increase, increase
- D. decrease, decrease

4. Voltage feedback connections tend to _____ the output impedance. Current feedback connections tend to _____ the output impedance.

- A. decrease, increase
- B. increase, decrease
- C. increase, increase
- D. decrease, decrease

5. With feedback, Î², the overall gain of the circuit is reduced by a factor _____ where A is the gain without the feedback.

- A. Î²
- B. AÎ²
- C. A
- D. 1 + Î²A

6. An amplifier with negative feedback has _____ bandwidth than (as) the amplifier without feedback.

- A. the same
- B. less
- C. more
- D. None of the above

7. A feedback amplifier has a _____ upper 3-dB frequency and a _____ lower 3-dB frequency compared to an amplifier without feedback.

- A. smaller, higher
- B. higher, smaller
- C. smaller, smaller
- D. higher, higher

8. What is the gain at the origin of the Nyquist plot?

- A. Zero
- B. A negative value
- C. A positive value
- D. Undefined

9. In a Nyquist plot, as the frequency increases, the phase shift between input and output signals _____.

- A. remains the same
- B. decreases
- C. increases
- D. None of the above

10. An amplifier is stable if the absolute magnitude of Î²A is _____.

- A. ∞
- B. less than 1
- C. greater than 1
- D. None of the above

11. In the Barkhausen criterion, the loop gain A is equal to _____.

- A. ∞
- B. 200,000
- C. 0
- D. 1

12. In practice, A is made _____ and the system is started oscillating by amplifying noise voltage, which is always present.

- A. greater than 1
- B. smaller than 1
- C. equal to 1
- D. None of the above

13. In the phase-shift oscillator, the gain of the amplifier stage must be _____.

- A. 0
- B. less than 29
- C. greater than 29
- D. ∞

14. In the phase-shift oscillator, the operating frequency is determined by _____.

- A. resistance only
- B. capacitance only
- C. LC combinations
- D. RC combinations

15. In the Wien bridge oscillator with R_{1} = R_{2} = R and C_{1} = C_{2} = C, a ratio of R_{3} to R_{4} will provide sufficient loop gain for the circuit to oscillate.

- A. 0
- B. 0.5
- C. 1
- D. 2

16. In the Colpitts oscillator, the frequency is determined by _____ .

- A. resistance only
- B. inductance only
- C. capacitance only
- D. both inductance and a capacitance

17. In the Colpitts oscillator, the elements X_{1} and X_{2} are _____ and X_{3} is a(n) _____.

- A. inductors, capacitor
- B. capacitors, inductor
- C. capacitors, resistor
- D. inductors, resistor

18. In a Hartley oscillator, the elements X_{1} and X_{2} are _____ and X_{3} is a(n) _____.

- A. inductors, capacitor
- B. capacitors, inductor
- C. capacitors, resistor
- D. inductors, resistor

19. Crystal oscillators are used whenever a(n) _____ level of stability is required.

- A. lower
- B. average
- C. greater
- D. None of the above

20. Since the crystal losses represented by R are small, the equivalent crystal Q (quality factor) is _____.

- A. very low
- B. low
- C. medium
- D. high

21. The series-resonant impedance of a crystal oscillator is _____.

- A. very low
- B. low
- C. medium
- D. very high

22. The parallel-resonant impedance of a crystal oscillator is _____.

- A. very low
- B. low
- C. medium
- D. very high

23. At the series-resonant frequency, the amount of positive feedback is _____.

- A. very large
- B. large
- C. small
- D. very small

24. _____ is a frequency-determining component in a unijunction oscillator.

- A. Total resistance
- B. Total capacitance
- C. Intrinsic stand-off ratio
- D. All of the above

25. Typically, a unijunction transistor has a stand-off ratio from _____ to _____.

- A. 0.0, 0.2
- B. 0.2, 0.4
- C. 0.4, 0.6
- D. 0.6, 0.8

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better you provide these questions with answers

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better you provide these questions with answers