## Multiple Choice Questions and Answers on Op-Amp ( Operational Amplifier )

**Q1. A differential amplifier ……………..**

- is a part of an Op-amp
- has one input and one output
- has two outputs
- answers (1) and (2)

**Answer : 4**

**Q 2. When a differential amplifier is operated single-ended, …………**

- the output is grounded
- one input is grounded and signal is applied to the other
- both inputs are connected together
- the output is not inverted

**Answer : 2**

**Q3. In differential-mode, …………….**

- opposite polarity signals are applied to the inputs
- the gain is one
- the outputs are of different amplitudes
- only one supply voltage is used

**Answer : 1**

**Q4. In the common mode, ……………**

- both inputs are grounded
- the outputs are connected together
- an identical signal appears on both the inputs
- the output signal are in-phase

**Answer : 3**

**Q5. The common-mode gain is ………..**

- very high
- very low
- always unity
- unpredictable

**Answer : 2**

**Q6. The differential gain is ………**

- very high
- very low
- dependent on input voltage
- about 100

**Answer : 1**

**Q7. If A _{DM} = 3500 and A_{CM} = 0.35, the CMRR is ……….**

- 1225
- 10,000
- 80 dB
- answers (1) and (3)

**Answer : 4**

**Q8. With zero volts on both inputs, an OP-amp ideally should have an output ………..**

- equal to the positive supply voltage
- equal to the negative supply voltage
- equal to zero
- equal to CMRR

**Answer : 3**

**Q9. Of the values listed, the most realistic value for open-loop voltage gain of an OP-amp is ……**

- 1
- 2000
- 80 dB
- 100,000

**Answer : 4**

**Q10. A certain OP-amp has bias currents of 50 μA. The input offset current is ……..**

- 700 nA
- 99.3 μA
- 49.7 μA
- none of these

**Answer : 1**

**Q11. The output of a particular Op-amp increases 8V in 12μs. The slew rate is …….**

- 90 V/μs
- 0.67 V/μs
- 1.5 V/μs
- none of these

**Answer : 2**

**Q12. For an Op-amp with negative feedback, the output is …….**

- equal to the input
- increased
- fed back to the inverting input
- fed back to the noninverting input

**Answer : 3**

**Q13. The use of negative feedback ………**

- reduces the voltage gain of an Op-amp
- makes the Op-amp oscillate
- makes linear operation possible
- answers (1) and (2)

**Answer : 4**

**Q14. Negative feedback ………..**

- increases the input and output impedances
- increases the input impedance and bandwidth
- decreases the output impedance and bandwidth
- does not affect impedance or bandwidth

**Answer : 2**

**Q15. A certain noninverting amplifier has R _{i} of 1 kΩ and R_{f} of 100 kΩ. The closed-loop voltage gain is ………**

- 100,000
- 1000
- 101
- 100

**Answer : 3**

**Q16. If the feedback resistor in Q15 (above question) is open, the voltage gain …….**

- increases
- decreases
- is not affected
- depends on R
_{i}

**Answer : 1**

**Q17. A certain inverting amplifier has a closed-loop voltage gain of 25. The Op-amp has an open-loop voltage gain of 100,000. If an Op-amp with an open-loop voltage gain of 200,000 is substituted in the arrangement, the closed-loop gain ……..**

- doubles
- drops to 12.5
- remains at 25
- increases slightly

**Answer : 3**

**Q18. A voltage follower ……….**

- has a voltage gain of 1
- is noninverting
- has no feedback resistor
- has all of these

**Answer : 4**

**Q19. The Op-amp can amplify**

- a.c. signals only
- d.c. signals only
- both a.c. and d.c. signals
- neither d.c. nor a.c. signals

**Answer : 3**

**Q20. The input offset current equals the ……….**

- difference between two base currents
- average of two base currents
- collector current divided by current gain
- none of these

**Answer : 1**

**Q21. The tail current of a differential amplifier is …….**

- half of either collector current
- equal to either collector current
- two times either collector current
- equal to the difference in base currents

**Answer : 3**

**Q22. The node voltage at the top of the til resistor is closes to ……….**

- collector supply voltage
- zero
- emitter supply voltage
- tail current times base resistance

**Answer : 2**

**Q23. The tail current in a differential amplifier equals …….**

- difference between two emitter currents
- sum of two emitter currents
- collector current divided by current gain
- collector voltage divided by collector resistance

**Answer : 2**

**Q24. The differential voltage gain of a differential amplifier is equal to RC divided by …….**

- r’
_{e} - r’
_{e}/2 - 2r’
_{e} - R
_{E}

**Answer : 3**

**Q25. The input impedance of a differential amplifier equals r’ _{e} times ……**

- β
- R
_{E} - R
_{C} - 2β

**Answer : 4**

**Q26. A common-mode signal is applied to ……….**

- the noninverting input
- the inverting input
- both iputs
- top of the tail resistor

**Answer : 3**

**Q27. The common-mode voltage gain is ………**

- smaller than differentail voltage gain
- equal to differential voltage gain
- greater than differential voltage gain
- none of the above

**Answer : 1**

**Q28. The input stage of an Op-amp is usually a ……….**

- differential amplifier
- class B push-pull amplifier
- CE amplifier
- swamped amplifier

**Answer : 1**

**Q29. The common-mode voltage gain of a differential amplifier is equal to R _{C }divided by ……..**

- r’
_{e} - 2r’
_{e} - r’
_{e}/2 - 2R
_{E}

**Answer : 4**

**Q30. Current cannot flow to ground through …….**

- a mechanical ground
- an a.c. ground
- a virtual ground
- an ordinary ground

**Answer : 3**