250+ TOP MCQs on Effects of Feedback and Answers

Analog Circuits Multiple Choice Questions on “Effects of Feedback”.

1. What is the reverse transmission factor?
A. Ratio of output by input signal
B. Ratio of feedback by input signal
C. Ration of feedback by output signal
D. Ratio of input by feedback signal

Answer: C
Clarification: In feedback systems, the feedback signal is in proportion with the output signal.
X_F ∝ X_O
X_F = βX_O, where β is the feedback factor or reverse transmission factor.

2. Return ratio for a circuit is 220. What is the amount of feedback, correct up to 2 decimal places?
A. 2.34 dB
B. – 46.84 dB
C. – 46.88 dB
D. 46.88 dB

Answer: C
Clarification: Return ratio is Aβ, where β=feedback factor, and A=open loop gain.
Amount of feedback is A_F/A = 1 + Aβ
In decibels, amount of feedback = -20log₁₀(1+Aβ) = -20log₁₀(221) = -46.88 decibels.

3. Consider the given diagram. Loop gain is 19. Consider closed loop gain is 50. Find the output without any feedback when input is 5.

A. 1000
B. 500
C. 5000
D. 50000

Answer: C
Clarification: Feedback factor, β=10.
A_F = A/(1+Aβ) = 50
A = 20*50 = 1000
Output is thus 5000.

4. Consider an open loop circuit with lower cutoff frequency 5kHz and upper cutoff frequency 20kHz. If negative feedback is applied to the same, choose correct option stating the new cutoff frequencies.
A. Lower cutoff = 5kHz, Upper cutoff = 20kHz
B. Lower cutoff = 2kHz, Upper cutoff = 18kHz
C. Lower cutoff = 2kHz, Upper cutoff = 25kHz
D. Lower cutoff = 10kHz, Upper cutoff = 25kHz

Answer: C
Clarification: Negative feedback decreases lower cutoff frequencies and increases the higher cutoff frequency.
f_HF = f_H(1+Aβ)
f_LF = f_L/(1+Aβ)
Total bandwidth is thus increased.

5. Find the relative change in gain with negative feedback given that return ratio is 24, and feedback factor is 3, when the change in open loop gain is 2.
A. 1
B. 1.6
C. 0.1
D. 0.01

Answer: D
Clarification: A_F = A/(1+Aβ)
Aβ = 24
A = 8
Relative change in gain = dA_F/A_F = dA/A(1+Aβ)
dA_F/A_F = 2/8*25 = 0.01.

6. Relative change of gain of feedback amplifier is 0.05. Also, loop gain is 9. Find desensitivity?
A. 50
B. 10
C. 20
D. 1/9

Answer: B
Clarification: We can simply use the ratio of 0.1 to find the answer.
Loop gain Aβ = 9
1+Aβ = 10
Desensitivity = 1/S = 1+Aβ = 10.

7. Circuit P has desensitivity 20, circuit Q has sensitivity 0.1 and circuit R has desensitivity 40. Which of the following is more stable in gain?
A. Circuit P
B. Circuit Q
C. Circuit R
D. All circuits are equally stable in gain

Answer: C
Clarification: Greater desensitivity indicates better stability in gain. More desensitivity means gain becomes smaller, but stable.
For circuit Q, desensitivity = 1/S = 10
Circuit R has higher desensitivity, hence most stable.

9. Consider the total harmonic distortion of a closed loop system is 5%. Distortion without feedback is 10%. Calculate the sensitivity of closed loop system.
A. 0.5
B. 0.2
C. 0.6
D. 0.1

Answer: A
Clarification: D_HF = D_H/1+Aβ
1 + Aβ = D_H/D_HF = 10/5 = 2
Sensitivity = (frac{1}{2}) = 0.5.

10. For the system shown gain with feedback is 200. Find feedback factor.

A. 0.41
B. 5
C. 0.0041
D. It can be any real number

Answer: C
Clarification: A_F = A/1+Aβ
A = A1 x A2 = 1200
Thus 1 + Aβ = 1200/200 = 6
Aβ = 5
β = 5/A = 0.0041.