# Voltage Series Feedback Amplifier MCQ [Free PDF] – Objective Question Answer for Voltage Series Feedback Amplifier Quiz

1. Specify the voltage gain of a non-inverting amplifier with feedback amplifier with and without feedback?

A. A= Vo/Vid, AF = Vf/Vo
B. A= Vf/Vid, AF= Vo/Vf
C. A= Vo/Vid, AF= Vo/Vin
D. A= Vf/Vid, AF = Vf/Vin

The voltage gain of an op-amp with feedback is the open-loop voltage gain, A=Vo /Vid. The voltage gain of op-amp without feedback is the closed-loop voltage gain, AF = Vo /Vin.

2. If the feedback voltage and the output voltage are given as 10v and 4v. Find the gain of the feedback circuit in the voltage-series feedback amplifier?

A. 2.5v
B. 40v
C. 3v
D. 6.2v

Gain of feedback

feedback voltage = 10 V

output voltage = 4V

B = Vf /Vo

= 10v/4v = 2.5v.

3. How is the difference voltage calculated in a closed-loop non-inverting amplifier?

A. Vid= Vo – Vf
B. Vid= Vin – Vf
C. Vid= Vo – Vin
D. Vid= Vf – Vin

Although the input is given to the non-inverting terminal of an op-amp, the difference voltage is equal to the input voltage minus feedback voltage is Vid= Vin – Vf.

4. Why the feedback circuit is said to be negative for voltage series feedback amplifier?

A. Feedback voltage is 180o out of phase with respect to an input voltage
B. Input voltage is 180o out of phase with respect to a feedback voltage
C. Feedback voltage is in the same phase with respect to an input voltage
D. Input voltage is in the same phase with respect to a feedback voltage

Voltage series feedback amplifiers have different voltages, Vid = Vin-Vf.

Therefore, the feedback voltage always opposes the input voltage and is out of phase by 180o with respect to the input voltage. Hence, the feedback is said to be negative.

5. Determine the closed-loop voltage gain from the given circuit. (Where gain of op-amp= 105).

A. 1090.9
B. 9821.43
C. 9166.66
D. 10000

The closed loop voltage gain

AF = {[A*(R4+R5)]/[(RF+R1+(A*R1)]}

= [105*(10kΩ+1kΩ)]/[1kΩ+10kΩ+(105*1kΩ)]

=11×108/112000

=> AF = 9821.43.

6. Express closed-loop voltage gain (AF) in terms of open-loop gain (A. and feedback circuit gain (B.?

A. AF = A/AB
B. AF = 1+ (A/AB.
C. AF = A/(1+AB.
D. AF = AB/(1+A.

The closed-loop voltage gain in terms of open-loop gain and feedback circuit gain is expressed as AF = A/(1+AB.

7. Which factor determines the gain of the voltage series feedback amplifier?

A. Open loop voltage gain
B. Feedback voltage
C. Ratio of two resistors
D. Gain of the feedback circuit

In setting the gain of the voltage series feedback amplifier, the ratio of two resistors is important and not the absolute value of these resistors.

For example: If a gain of 11 is desired, we choose R1=1kΩ and R1=10kΩ or R1=100Ω and RF= 1kΩ.

8. For the feedback circuit of the voltage series feedback amplifier, find the feedback voltage for the specifications: R1=1kΩ, RF = 10kΩ, and Vo= 25v.

A. 12.5v
B. 22v
C. 0.9v
D. 2.3v

The feedback voltage

Vf = (R1*Vo)/(R1+RF)

= (1kΩ*25v)/(1kΩ+10kΩ)

= 2.272v ≅ 2.3v.

9. What must be the value of external components used in the voltage series feedback amplifier?

A. Less than 1MΩ
B. Less than 10MΩ
C. Less than 100MΩ
D. Less than 0.1MΩ

All external components’ values should be less than 1MΩ. So, that they do not adversely affect the internal circuitry of the op-amp.

10. Define the input resistance with feedback for the voltage series feedback amplifier?

A. RIF = (1-AB.
B. RIF = (AB-1)
C. RIF = (1+AB.
D. None of the mentioned

In the feedback amplifier, the input resistance of the op-amp with feedback is (1+AB. times that of without feedback.

11. When the non-inverting input terminal of an op-amp is equal to that of the inverting input terminal (ideally)

A. a–>∞
B. Vid ≅ 0
C. AF = 1+( RF / R1)
D. All of the mentioned

When the input at both the terminal are equal, the difference input voltage,

Vid=Vin1– Vin2.

=> Vid≅0 (∵Vin1= Vin2)

The open loop voltage gain, A= Vo/ Vid = Vo/0 = ∞ and

the closed loop voltage gain, AF= Vo/ Vin = 1+ (RF/ R1).

12. Find the input and output resistance for the circuit shown.
Specification for 741 op-amp : A=400000 ; Ri = 33MΩ; Ro = 60Ω;
RF = 11kΩ; R1 = 2kΩ; Supply voltage = ± 15v; Maximum output voltage swing = ± 13v.

A. RIF = 66MΩ, ROF = 30Ω
B. RIF = 30MΩ, ROF = 6kΩ
C. RIF = 15kΩ, ROF = 50MΩ
D. None of the mentioned

AF = 1+(RF/R1) = 1+(11kΩ/2kΩ) = 6.5;

B= 1/ AF = 1/6.5 = 0.154;

Input resistance of RIF = R1(1+AB. = 33MΩ[1+(6.5*0.154) ]= 66MΩ;

Output resistance of ROF = Ro/(1+AB. = 60/[1+(6.5*0.154) ]= 29.98 ≅30Ω.

13. The output resistance of the op-amp with feedback is

A. Same as that of the output resistance without feedback
B. Greater than that of the output resistance without feedback
C. Smaller than that of the output resistance without feedback
D. None of the mentioned

In a voltage series feedback amplifier, the output resistance is (1/(1+AB.) times the output resistance of the op-amp. Therefore, the output resistance of the op-amp with feedback is much smaller than the output resistance without feedback.

14. Find the output current in the voltage series feedback amplifier.

A. io ={ [Vo+(A*Vid)]/Ro}
B. io ={ [Vo-(A*Vid)]/Ro}
C. io =(Vo/Ro)*A
D. io =[A*(Vo-Vid)]/Ro

The output current in the voltage series feedback amplifier is given as

io ={[Vo-(A*Vid)]/Ro}.

15. Find the unity-gain bandwidth for the voltage series feedback amplifier?

A. UBG = Afo
B. UBG = AfF
C. UBG = Afo fF
D. UBG = AFfo

The unity-gain bandwidth is given as the product of open-loop voltage gain and breaks the frequency of an op-amp.

16. The bandwidth of a non-inverting amplifier with feedback is equal to

A. fo(AB.
B. fo(AB-1)
C. fo(1+AB.
D. fo(1-AB.

The bandwidth of the non-inverting amplifier with feedback is equal to its bandwidth without feedback times (1+AB.. i.e. fF=fo(1+AB.

17. How are the saturation voltage specified on the manufacturer’s datasheet?

A. Negative voltage
B. Output voltage swing
C. Supply voltage
D. None of the mentioned

In an open-loop op-amp, the total output offset voltage (i.e. output voltage swing) is equal to either the positive or negative saturation voltage.

18. What is the formula for total output offset voltage with feedback?

A. Voot = ± Vo/(1+AB.
B. Voot = ± Vsat*(1+AB.
C. VooT = ± Vsat/(1+AB.
D. Voot = ± Vo*(1+AB.

The total output offset voltage with feedback = (Total output offset voltage witput feedback) / (1+AB.. i.e. VooT = ± Vsat/(1+AB).

19. Which of the following has the same characteristic as that of the non-inverting amplifier with feedback?

A. Perfect feedback amplifier
B. Voltage follower
C. Perfect voltage amplifier
D. All of the mentioned

A perfect voltage amplifier has very high input resistance, very low output resistance, stable voltage gain, large bandwidth, and very little output offset voltage.

From the analysis of the characteristic of the non-inverting amplifier with feedback, it is clear that it exhibits the characteristics of a perfect voltage amplifier.

20. What is the gain of voltage follower?

A. Gain > ∞
B. Gain –>1
C. Gain <1
D. Gain –>∞

A voltage follower is a non-inverting amplifier configured for unity gain. Such that the output voltage is equal to and in phase with the input.

21. Which is preferred to attain higher input resistance and the output amplitude equal to input?

A. Voltage follower
B. Voltage series feedback amplifier
C. Voltage shunt feedback amplifier
D. Inverter

In the voltage follower, the output follows the input due to unity gain. Therefore, it is attained to get higher input resistance and output amplitude equal to the input.

22. Find the input and output voltage in voltage follower circuit?

A. Vin=2v and Vout = 3v
B. Vin=10v and Vout = 11v
C. Vin=9v and Vout = 9v
D. Vin=4v and Vout = 7v

The voltage follower has an input voltage equal to an output voltage. The closed-loop voltage gain is equal to one. For example, take the input and output voltage to be 2v, then

AF = Vout/Vin = 2v/2v = 1.

23. Voltage follower is also called as

A. None of the mentioned
B. Non-inverting amplifier
C. Inverting amplifier
D. Normal buffer

The voltage follower is also called a non-inverting buffer because, when placed between two networks, it removes the loading on the first network.

24. Find the bandwidth and total output offset voltage of a voltage follower? The following are the specifications for the op-amp 741: A=200000, fo =5hz, and supply voltage =±15v.

A. fF = 1000hz, VooT = ± 7.5µv.
B. fF = 100khz, VooT = ± 7.5µv.
C. fF = 10khz, VooT = ±7.5µv.
D. fF = 1000khz, VooT = ± 7.5µv.