OP AMP - part 1

The OPAMP related objective questions are given in this post with answers.

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

Ans: 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

Ans: 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

Ans: 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

Ans: 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
 
 Ans: 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=∞

  Ans: A. 
7.Calculate the cutoff frequency of a first-order low-pass filter for R1 = 2.5kΩ  and C1 = 0.05μF
A. 1.273kHz
B. 12.73kHz
C. 127.3 kHz
D. 127.3 Hz

Ans: A. 
Hint: low pass filter cut off frequency f = 1/(2πRC)
8. How many op-amps are required to implement this equation

A. 2
B. 3
C. 4
D. 1

Ans: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

Ans: D. The voltage follower which has one opamp has the output of Vo = Vin
10. An OPAMP has a slew rate of 5 V/μ 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

Ans: D
Hint: Slew rate is defined as the max. rate of change of output voltage. Its unit is V/μS.
Time period = 1/f = 1/1MHz = 1μS
V= Vm. sin(ωt) = Vm. sin(2πf.t)
slew rate = dV/dt = d(Vm. sin(2πf.t)/ dt=Vm. 2πf. cost...

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