**OP AMP Questions :-**

**1. A differential amplifier ……………..**

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

**Ans : 4**

**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

**Ans : 2**

**3. 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

**Ans : 1**

**4. 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

**Ans : 3**

**5. The common-mode gain is ………..**

very high

very low

always unity

unpredictable

**Ans : 2**

**6. The differential gain is ………**

very high

very low

dependent on input voltage

about 100

**Ans : 1**

**7. If ADM = 3500 and ACM = 0.35, the CMRR is ……….**

1225

10,000

80 dB

answers (1) and (3)

**Ans : 4**

**8. 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

**Ans : 3**

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

1

2000

80 dB

100,000

**Ans : 4**

**10. 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

**Ans : 1**

**11. 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

**Ans : 2**

**12. 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

**Ans : 3**

**13. 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)

**Ans : 4**

**14. 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

**Ans : 2**

**15. A certain noninverting amplifier has Ri of 1 kO and Rf of 100 kO. The closed-loop voltage gain is ………**

100,000

1000

101

100

**Ans : 3**

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

increases

decreases

is not affected

depends on Ri

**Ans : 1**

**17. 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

**Ans : 3**

**18. A voltage follower ……….**

has a voltage gain of 1

is noninverting

has no feedback resistor

has all of these

**Ans : 4**

**19. 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

**Ans : 3**

**20. 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

**Ans : 1**

**21. 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

**Ans : 3**

**22. 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

**Ans : 2**

**23. 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

**Ans : 2**

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

r’e

r’e/2

2r’e

RE

**Ans : 3**

**25. The input impedance of a differential amplifier equals r’e times ……**

ß

RE

RC

2ß

**Ans : 4**

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

the noninverting input

the inverting input

both iputs

top of the tail resistor

**Ans : 3**

**27. 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

**Ans : 1**

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

differential amplifier

class B push-pull amplifier

CE amplifier

swamped amplifier

**Ans : 1**

**29. The common-mode voltage gain of a differential amplifier is equal to RC divided by ……..**

r’e

2r’e

r’e/2

2RE

**Ans : 4**

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

a mechanical ground

an a.c. ground

a virtual ground

an ordinary ground

**Ans : 3**