ELECTRONICS ENGINEERING - OPERATIONAL AMPLIFIER (OP-AMP) MCQs

This section of  Electronics engineering  Multiple Choice  Questions and Answers  (MCQs) focuses on the  “ Operational Amplifier(OP-AMP)  ”....

This section of Electronics engineering Multiple Choice Questions and Answers (MCQs) focuses on the “ Operational Amplifier(OP-AMP) ”. These MCQs are very helpful for the preparation of  University exams, Engineering exams, and various Technical competitive exams.

 ELECTRONICS - OPERATIONAL AMPLIFIER (OPAMP) MCQs

1. The output of an integrator is given as:

A) `V_O\=-\frac1{RC}\int_0^t\V_{i\}dt`
B) `V_O\=+\frac1{RC}\int_0^t\V_{i\}dt`
C) `V_O\=+RC\int_0^t\V_{i\}dt`
D) `V_O\=-RC\int_0^t\V_{i\}dt`

ANSWER= (A) `-V_O\=-\frac1{RC}\int_0^t\V_{i\}dt`
Explanation:-Integrator is a circuit in which output voltage waveform is the integral of the input voltage waveform and is given as `V_O\=-\frac1{RC}\int_0^t\V_{i\}dt`

 

2. If the output of opamp changes by 30 V in 6 µs then the slew rate is :

A) 18 V/µs
B) 10 V/µs
C) 5 V/µs
D) None

ANSWER= (C) 5 V/µs
Explanation:- slew rate is defined as the maximum rate of change of output with respect to time. Its unit is V/µs, so SR=`\frac{dv_O}{dt}`

 

3. If the common mode gain is 0.27 and diffrential voltage gain is 2700, the CMRR is:

A) 40dB
B) 80dB
C) 10000
D) both B and C

ANSWER= (D) both B and C
Explanation:- CMRR is defined as the ratio of differential voltage gain (A_d)to the common-mode gain (A_c)
so , CMRR =A_d/A_c =2700/0.27 = 10000
CMRR in dB = 20log₁₀CMRR = 20log₁₀10000= 80dB.

 

4. Identify the given circuit:

A) Voltage follower
B) Unity gain amplifier
C) Buffer amplifier
D) All of these

ANSWER= (D) All of these
Explanation:-The given circuit is a noninverting amplifier with R_f= 0 and R_i= ∞ .
So output voltage V_o=(1+R_f/R_i)V_i= (1+ 0/∞)V_i =V_i
since output voltage is same as the input voltage and also gain is equal to 1 ,that's why this circuit is called a voltage follower 0r unity gain amplifier. As it only provides a means of isolating an input signal from a load ,so it is also known as a Buffer amplifier

 

5. The bandwidth of an ideal opamp is:

A) zero
B) ∞
C) unity
D) 10⁵Hz

ANSWER= (A) ∞
Explanation:- The bandwidth of an ideal opamp should be infinite, so that any frequency signal ranging from o to ∞ Hz may be amplified without any attenuation.

 

6. An opamp has a feedback resistance R_F=20kΩ and the resistance in the input side on inverting terminals are R₁=20kΩ, R₂=10kΩ, R₃=5kΩ. The corresponding inputs are V_i1= +8V , V_i2= -2V , V_i3= +1V. The non-inverting terminal is grounded then the output voltage is:

A) 16V
B) 4V
C) 8V
D) -8V

ANSWER= (D) -8V
Explanation:- When all inputs are applied on the same terminal of opamp then the circuit act as an adder. So the output of the adder is given as
V_o= -R_F[V_i1/R₁ + V_i2/R₂ + V_i3/R₃]=-20[+8/20 + (-2)/10 +1/5]= -8V.

 

7. In an opamp used as a differentiator R=1MΩ and C=2µF. If a signal V_i=2sin2000πt mV is used as input voltage then the output voltage is:

A) 4π cos2000πt mV
B) -8π cos2000πt V
C) 2π cos2000πt V
D) -8π sin2000πt mV

ANSWER= (B) -8π cos2000πt mV
Explanation:- The output equation of differentiator is given as
V_o= -RC d(v_i)/dt = -1x10⁶ x 2x10^-6d(2sin2000πt)/dt= - 8000π cos2000πt mV = - 8π cos2000πt V

 

8. Opamp amplifies the difference between the voltages applied at the non-inverting input and inverting input.

A) True
B) False

ANSWER= (A) True
Explanation:- Opamp amplifies the difference between the two input voltages applied at the non-inverting and inverting terminals. It does not amplify the input voltages themselves.

 

9. The number of pin in 741 opamp IC is:

A) 16
B) 32
C) 8
D) 4

ANSWER= (C) 8
Explanation:- The 741 op-amp IC has 8 pins. The function of each pin is listed below:
Pin 1: offset null
Pin 2:Inverting Input
Pin 3:Non-inverting Input
Pin 4:Negative power supply(V-)
Pin 5:offset null
Pin 6:output
Pin 7:positive power supply(V+)
Pin 8:No connection(NC)

 

10. The input and output resistance of an ideal opamp is :

A) zero, zero
B) zero, infinity
C) infinity, zero
D) infinity, infinity

ANSWER= (C) infinity , zero
Explanation:- In an ideal opamp:
(i)Differential voltage gain, input resistance, slew rate, and CMRR are equal to infinity
(ii))Output resistance, Common mode voltage gain, offset voltage, and power supply rejection ratio(PSRR)are equal to zero.