Amplifiers

An Amplifier is an electronic device or circuit which is used to increase the magnitude of the signal applied to its input.

Gain of an Amplifier:
  • Voltage gain (A$_v$) = $\dfrac{\mathrm{Output\ voltage}}{\mathrm{Input\ voltage}}$
  • Current gain: (A$_i$) = $\dfrac{\mathrm{Output\ current}}{\mathrm{Input\ current}}$
  • Power gain = A$_v$ $\times$ A$_i$

Solved Example:

9912-01

As compared to FET, BJT has ________ input impedance and ________ output impedance. (UPPCL JE Paper 5- Nov 2016)

Correct Answer: B

Solved Example:

9912-02

An Amplifier circuit of voltage gain 100 gives 10V output, the value of input voltage is: (VSSC ISRO Tech B Dec 2012)

Correct Answer: B

Solved Example:

9912-03

The output voltage of a voltage amplifier is found to decrease by 20% when a load resistance of 1 K$\Omega$ is connected. What is the output resistance of the amplifier? (ISRO VSSC Tech Asst Electronics 2019)

Correct Answer: B

Solved Example:

9912-04

The power input to an amplifier is 2 $\mu$W. The power gain of the amplifier is 40 dB. The output power of amplifier is: (LPSC ISRO Tech Asst Electronics Feb 2020)

Correct Answer: D

Solved Example:

9912-05

The efficiency of a class B push-pull amplifier is: (URSC ISRO Tech B Nov 2016)

Correct Answer: D

Solved Example:

9912-06

In an amplifier, the signal handling capacity will be high when the operating point is selected: (RSMSSB JE Elec Nov 2020)

Correct Answer: D

Solved Example:

9912-07

Negative feedback in an amplifier: (BSNL JE TTA Sep 2016 Shift I)

Correct Answer: A

Solved Example:

9912-08

Find P$_{in}$ for an amplifier with a power gain of 20 and an output power of 1 W. (NLC GET ECE Nov 2020)

Correct Answer: A

Solved Example:

9912-09

Overmodulation of transmitter signal is corrected by the adjustment of the: (BSNL JE (TTA) Sep 2016 Shift I)

Correct Answer: A

Solved Example:

9912-10

When amplifiers are cascaded: (IPRC ISRO Tech Electronics Aug 2016)

Correct Answer: C