# ELECTRICAL ENGINEERING IMPORTANT MCQ-OPAMP CIRCUITS

1. A non inverting closed loop op amp circuit generally has a gain factor

A. Less than one

B. Greater than one

C. Of zero

D. Equal to one

Answer :- B. For non inverting amplifier the gain is A = 1 + (Rf/Rin)). So it will be always more than one

2. If ground is applied to the (+) terminal of an inverting op-amp, the (–) terminal will

A. Not need an input resistor

B. Be virtual ground

C. Have high reverse current

D. Not invert the signal

Answer :- B. Other options are not suitable.

3. The closed-loop voltage gain of an inverting amplifier equal to

A. The ratio of the input resistance to feedback resistance

B. The open-loop voltage gain

C. The feedback resistance divided by the input resistance

D. The input resistance

Answer :- C

4. When a number of stages are connected in parallel, the overall gain is the product of the individual stage gains

A. True

B. False

Answer :- B

5. An ideal OP-AMP is an ideal

a) Current controlled Current source

b) Current controlled voltage source

c) Voltage controlled voltage source

d) voltage controlled current source

Answer :- C. The ideal Opamp output voltage is maintained constant. It is controlled by input voltage.

6. The ideal OP-AMP has the following characteristics.

a) Ri=∞ ,A=∞ ,R0=0

b) Ri=0 ,A=∞ ,R0=0

c) Ri=∞ ,A=∞ ,R0=∞

d) Ri=0 ,A=∞ ,R0=∞

Answer :- A.

7.Calculate the cutoff frequency of a first-order low-pass filter for R1 = 2.5kÎ© and C1 = 0.05Î¼F

A. 1.273kHz

B. 12.73kHz

C. 127.3 kHz

D. 127.3 Hz

Answer :- A.

Hint: low pass filter cut off frequency f = 1/(2Ï€RC)

8. How many op-amps are required to implement this equation Vo= - (RfV1/R1+RfV2/R2+RfV3/R3)

B. 3

C. 4

D. 1

Answer :-D. The output voltage of inverting amplifier is Vout = (-Rf/Rin)Vin. By keeping 1 inverting amplifier and three no of sources (V1, V2, V3) in series corresponding input resistors(R1, R2, R3), we can get this equation.

9. How many op-amps are required to implement this equation Vo = V1

A. 4

B. 3

C. 2

D. 1

Answer :- D. The voltage follower which has one opamp has the output of Vo = Vin

10. An OPAMP has a slew rate of 5 V/Î¼ S .The largest sine wave O/P voltage possible at a frequency of 1 MHZ is

A. 10 volts

B. 5 volts

C. 5/ volts

D. 5/2 volts

Answer :- D

Hint: Slew rate is defined as the max. rate of change of output voltage. Its unit is V/Î¼S.

Time period = 1/f = 1/1MHz = 1Î¼S

V= Vm. sin(Ï‰t) = Vm. sin(2Ï€f.t)

slew rate = dV/dt = d(Vm. sin(2Ï€f.t)/ dt=Vm. 2Ï€f. cost…

11) An ideal OP-AMP is an ideal

A. Current controlled Current source

B. Current controlled Voltage source

C. Voltage controlled Voltage source

D. Voltage controlled Current source

Answer :- C

12) A 741-Type OP-AMP has a gain-bandwith product of 1MHz. A non-inverting amplifier using this opamp & having a voltage gain of 20db will exhibit -3db bandwidth of

A. 50KHz

B. 100KHz

C. 1000/17KHz

D. 1000/7.07KHz

Answer :- A

13) An amplifier using an opamp with slew rate SR=1v/sec has a gain of 40db.If this amplifier has to faithfully amplify sinusoidal signals from dc to 20KHz without introducing any slew-rate induced distortion, then the input signal level exceed

A. 795mV

B. 395mV

C. 795mV

D. 39.5mV

Answer :- C

14) The ideal OP-AMP has the following characteristics

A. Ri=∞,A=∞,R0=0

B. Ri=0,A=∞,R0=0

C. Ri=∞,A=∞,R0=∞

D. Ri=0,A=∞,R0=∞

Answer :- A

15) The approximate input impedance of the opamp circuit which has Ri=10k, Rf=100k, RL=10k

A. ∞

B. 120k

C. 110k

D. 10k

Answer :- C

16) An opamp has a slew rate of 5V/ S. the largest sine wave o/p voltage possible at a frequency of 1MHz is

A. 10 V

B. 5 V

C. 5V

D. 5/2 V

Answer :- A

7) Assume that the op-amp of the fig. is ideal. If Vi is a triangular wave, then V0 will be

A. Square wave

B. Triangular wave

C. Parabolic wave

D. Sine wave

Answer :- D

18) A differential amplifier is invariably used in the i/p stage of all op-amps. This is done basically to provide the op-amps with a very high

A. CMMR

B. Bandwidth

C. Slew rate

D. Open-loop gain

Answer :- C

19) A differential amplifier has a differential gain of 20,000. CMMR=80dB. The common mode gain is given by

A. 2

B. 1

C. 1/2

D. 0

Answer :- A

20) In the differential voltage gain & the common mode voltage gain of a differential amplifier are 48db & 2db respectively, then its common mode rejection ratio is

A. 23dB

B. 25dB

C. 46dB

D. 50dB

Answer :- C

21) Which of the following amplifier is used in a digital to analog converter?

(a) Non inverter

(b) Voltage follower

(c) Summer

(d) Difference amplifier

Answer :- C

22) Differential amplifiers are used in

(a) Instrumentation amplifiers

(b) Voltage followers

(c) Voltage regulators

(d) Buffers

Answer :-A

23) For an ideal op-amp, which of the following is true?

(a) The differential voltage across the input terminals is zero

(b) The current into the input terminals is zero

(c) The current from output terminal is zero

(d) The output resistance is zero

Answer :- C

24) The two input terminals of an opamp are labeled as

a) High and low

b) Positive and negative

c) Inverting and non inverting

d) Differential ans non differential

Answer :-C

25) When a step-input is given to an op-amp integrator, the output will be

(a) A ramp.

(b) A sinusoidal wave.

(c) A rectangular wave.

(d) A triangular wave with dc bias

Answer :- A

26) For an op-amp having differential gain Av and common-mode gain Ac the CMRR is given by

A. Av + Ac

B. Av / Ac

C. 1 + Av / Ac)

D. Ac / Av

Answer :-B

27) Hysteresis is desirable in Schmitt-trigger, because

A. Energy is to be stored/discharged in parasitic capacitances.

B. Effects of temperature would be compensated.

C. Devices in the circuit should be allowed time for saturation and desaturation.

D. It would prevent noise from causing false triggering.

Answer :- C

28) The output voltage Vo of the above circuit is

(a) -6V

(b) -5V

(c) -1.2V

(d) -0.2V

Answer :- B

29) In the above circuit the current ix is

(a) 0.6A

(b) 0.5A

(c) 0.2A

(d) 1/12A

Answer :- B

30) Op-amp circuits may be cascaded without changing their input output relationships

(a) True

(b) False

Answer :- A

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