Operational Amplifier(OP-AMP)&its Applications MCQs

This section of Electronics engineering Multiple Choice Questions and Answers (MCQs) focuses on the “ Operational Amplifier(OP-AMP) and its application as an adder, integrator, differentiator, etc.  ”. These MCQs are very helpful for the preparation of  University exams, Engineering exams, and various Technical competitive exams. It is advised that before solving these MCQs one must have a basic understanding of opamp. CLICK HERE to learn the basics of Opamp.

 ELECTRONICS – OPERATIONAL AMPLIFIER (OPAMP) MCQs

1. The output of an integrator is given as:

A)V_O\;=-\frac1{RC}\int_0^tV_{in}\operatorname dt
B) V_O\;=+\frac1{RC}\int_0^tV_{in}\operatorname dt
C) V_O\;=+\;RC\int_0^tV_{in}\operatorname dt
D) V_O\;=-RC\int_0^tV_{in}\operatorname dt

ANSWER= (A) V_O\;=-\frac1{RC}\int_0^tV_{in}\operatorname 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^tV_{in}\operatorname dt
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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\;={\left.\frac{dv_o}{dt}\right|}_{max}
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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.
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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
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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.
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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.
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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 = -1×10⁶ x 2×10^-6d(2sin2000πt)/dt= – 8000π cos2000πt mV = – 8π cos2000πt V
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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.
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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)

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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.
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