# Amplifiers – Exercise – 1

1. The important characteristic of emitter-follower is :

(a)  high input impedance and high output impedance
(b)  high input impedance and low output impedance
(c)  low input impedance and low output impedance
(d)  low input impedance and high output impedance

Explanation
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2. Most of linear ICs are based on the two transistor differential amplifier because of its :

(a)  input voltage dependent linear transfer characteristic
(b)  high voltage gain
(c)  high input resistance
(d)  high CMRR

Explanation
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3. The maximum possible collector circuit efficiency of an ideal class A power amplifier is :

(a)  15%
(b)  25%
(c)  50%
(d)  75%

Explanation
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4. If the feedback signal is returned to the input in series with the applied voltage, the input impedance :

(a)  decreases
(b)  increases
(c)  does not change
(d)  becomes infinity

Explanation
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5. In an amplifier with negative feedback, the bandwidth is :
where A = gain of the basic amplifier and β = feedback factor

(a)  increased by a factor of β
(b)  decreased by a factor of β
(c)  increased by a factor of (1+Aβ)
(d)  not affected at all by the feedback

Explanation
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6. The overall bandwidth of two identical voltage amplifiers connected in cascade will :

(a)  remain the same as that of a single stage
(b)  be worse than that of a single stage
(c)  be better than that of a single stage
(d)  be better if stage gain is low and worse if stage gain is high

Explanation
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7. Negative feedback in an amplifier :

(a)  reduces the voltage gain
(b)  increases the voltage gain
(c)  does not affect the voltage gain
(d)  converts the amplifier into an oscillator

Explanation
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8. In a voltage shunt negative feedback amplifier system, the input resistance Ri and the output resistance Ro of the basic amplifier are modified as follows :

(a)  Ri is decreased and Ro increased
(b)  both Ri and Ro are decreased
(c)  both Ri and Ro are increased
(d)  Ri is increased and Ro is decreased

Explanation
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9. A radio frequency signal contains three frequency components, 870 KHz, 875 KHz and 880 KHz. The signal needs to be amplified. The amplifier used should be :

(a)  audio frequency amplifier
(b)  wide band amplifier
(c)  tuned voltage amplifier
(d)  push-pull amplifier

Explanation
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10. The type of power amplifier which exhibits crossover distortion in its output is :

(a)  Class A
(b)  Class B
(c)  Class AB
(d)  Class C

Explanation
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11. In class–A amplifier, the output current flows for :

(a)  a part of the cycle or the input signal
(b)  the full cycle of the input signal
(c)  half the cycle of the input signal
(d)  3/4th of the cycle of the input signal

Explanation
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12. When an amplifier is provided with current series feedback, its :

(a)  input impedance increases and output impedance decreases
(b)  input and output impedances both decrease
(c)  input impedance decreases and output impedance increases
(d)  input and output impedances both increase

Explanation
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13. A differential amplifier, amplifies :

(a)  the mathematically differentiates the average of the voltages on the two input lines
(b)  the differentiates the input waveform on one line when the other line is grounded
(c)  the difference of voltages between the two input lines
(d)  the differentiates the sum of the two input waveforms

Explanation
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14. The common collector amplifier is also known as :

(a)  collector follower
(b)  base follower
(c)  emitter follower
(d)  source follower

Explanation
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15. The upper cutoff frequency of an RC coupled amplifier mainly depends upon :

(a)  coupling capacitor
(b)  emitter bypass capacitor
(c)  output capacitance of signal source
(d)  inter-electrode capacitance and stray shunt capacitance

Explanation
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16. Two stages of BJT amplifiers are cascaded by RC coupling. The voltage gain of the first stage is 10 and that of the second stage is 20. The overall gain of the coupled amplifier is :

(a)  10×20
(b)  10+20
(c)  (10+20)2
(d)  (10×20)/2

Explanation
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(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
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18. The current amplification factor in CE configuration is :

(a)  α
(b)  β+ 1
(c)  1/β
(d)  β

Explanation
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19. When negative voltage feedback is applied to an amplifier, its voltage gain …………

(a)  is increased
(b)  is reduced
(c)  remains the same
(d)  none of the above

Explanation
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20. The value of negative feedback fraction is always ……….

(a)  less than 1
(b)  more than 1
(c)  equal to 1
(d)  none of the above

Explanation
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(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
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22. The gain of an amplifier without feedback is 100 db. If a negative feedback of 3 db is applied, the gain of the amplifier will become ……..

(a)  101.5 db
(b)  300 db
(c)  103 db
(d)  97 db

Explanation
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23. If the feedback fraction of an amplifier is 0.01, then voltage gain with negative voltage feedback is approximately …….

(a)  500
(b)  100
(c)  1000
(d)  5000

Explanation
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24. A feedback circuit usually employs ………. network.

(a)  resistive
(b)  capacitive
(c)  inductive
(d)  none of the above

Explanation
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25. The gain of an amplifier with feedback is known as ……….. gain.

(a)  resonant
(b)  open loop
(c)  closed loop
(d)  none of the above

Explanation
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26. When voltage feedback (negative) is applied to an amplifier, its input impedance …….

(a)  is decreased
(b)  is increased
(c)  remains the same
(d)  none of the above

Explanation
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27. When current feedback (negative) is applied to an amplifier, its input impedance ………

(a)  is decreased
(b)  is increased
(c)  remains the same
(d)  none of the above

Explanation
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28. Negative feedback is employed in …….

(a)  oscillators
(b)  rectifiers
(c)  amplifiers
(d)  none of the above

Explanation
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29. Emitter follower is used for ……..

(a)  current gain
(b)  impedance matching
(c)  voltage gain
(d)  none of the above

Explanation
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30. The voltage gain of an emitter follower is …

(a)  much less than 1
(b)  approximately equal to 1
(c)  greater than 1
(d)  none of the above

Explanation
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31. When current feedback (negative) is applied to an amplifier, its output impedance ……

(a)  is increased
(b)  is decreased
(c)  remains the same
(d)  none of the above

Explanation
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32. Emitter follower is a …………… circuit.

(a)  voltage feedback
(b)  current feedback
(c)  both voltage and current feedback
(d)  none of the above

Explanation
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33. If voltage feedback (negative) is applied to an amplifier, its output impedance ……..

(a)  remains the same
(b)  is increased
(c)  is decreased
(d)  none of the above

Explanation
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34. When negative voltage feedback is applied to an amplifier, its bandwidth ……..

(a)  is increased
(b)  is decreased
(c)  remains the same
(d)  insufficient data

Explanation
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35. An emitter follower has ….. input impedance.

(a)  zero
(b)  low
(c)  high
(d)  none of the above

Explanation
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36. If voltage gain without feedback and feedback fraction are Av and mv respectively, then gain with negative voltage feedback is ……..

(a)  Av/(1-Avmv)
(b)  Av/(1+Avmv)
(c)  (1+Avmv)/Av
(d)  (1 + Av mv) Av

Explanation
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37. The output impedance of an emitter follower is ……..

(a)  high
(b)  very high
(c)  almost zero
(d)  low

Explanation
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38. The approximate voltage gain of an amplifier with negative voltage feedback (feedback fraction being mv) is ………

(a)  1/mv
(b)  mv
(c)  1 /(1 + mv)
(d)  1 – mv

Explanation
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39. If Av and Afb are the voltage gains of an amplifier without feedback and with negative feedback respectively, then feedback fraction is …….

(a)  (1/Av) – (1/Afb)
(b)  (1/Av) + (1/Afb)
(c)  (Av/Afb) + (1/Av)
(d)  (1/Afb) – (1/Av)

Explanation
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40. In the expression for voltage gain with negative voltage feedback, the term 1 + Am mv is known as ……..

(a)  gain factor
(b)  feedback factor
(c)  sacrifice factor
(d)  none of the above

Explanation
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41. If the output impedance of an amplifier is Zout without feedback, then with negative voltage feedback, its value will be ………..

(a)  Zout/(1+Avmv)
(b)  Zout (1+Avmv)
(c)  (1+Avmv)/Zout
(d)  Zout (1-Avmv)

Explanation
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42. If the input impedance of an amplifier is Zin without feedback, then with negative voltage feedback, its value will be ………..

(a)  Zin/(1+Avmv)
(b)  Zin (1 + Av mv)
(c)  (1+Avmv)/Zin
(d)  Zin (1 – Av mv)

Explanation
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43. Feedback circuit ……… frequency.

(a)  is independent of
(b)  is strongly dependent on
(c)  is moderately dependent on
(d)  none of the above

Explanation
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44. The basic purpose of applying negative voltage feedback is to ………

(a)  increase voltage gain
(b)  reduce distortion
(c)  keep the temperature within limits
(d)  none of the above

Explanation
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45. If the voltage gain of an amplifier without feedback is 20 and with negative voltage feedback it is 12, then feedback fraction is ……..

(a)  5/3
(b)  3/5
(c)  1/5
(d)  0.033

Explanation
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46. In an emitter follower, we employ …… negative current feedback

(a)  50%
(b)  25%
(c)  100%
(d)  75%

Explanation
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47. An amplifier has an open loop voltage gain of 1,00,000. With negative voltage feedback, the voltage gain is reduced to 100. What is the sacrifice factor ?

(a)  1000
(b)  100
(c)  5000
(d)  none of the above

Explanation
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48. In the above question, what will happen to circuit performance ?

(a)  distortion is increased 1000 times
(b)  input impedance is increased 1000 times
(c)  output impedance is increased 1000 times
(d)  none of the above

Explanation
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49. The non-linear distortion of an amplifier is D without feedback. The amplifier has an open-loop voltage gain of Av and feedback fraction is mv. With negative voltage feedback, the non-linear distortion will be …….

(a)  D (1 + Av mv)
(b)  D (1 – Av mv)
(c)  (1 + A m)/D
(d)  1 D/(1 + Avmv)