JEE Main 2019 · Physics · Semiconductors and Communication · easy

A common-emitter transistor amplifier has a current gain β=50, an input resistance of 500 Ω and an output load resistance of 5 kΩ. The power gain of…

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A common-emitter transistor amplifier has a current gain

\beta=50

, an input resistance of

500\ \Omega

and an output load resistance of

5\ \mathrm{k\Omega}

. The power gain of the amplifier is

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Answer: (A) $25000$

The voltage gain of a common-emitter amplifier is

A_V=\beta\dfrac{R_{out}}{R_{in}}=50\times\dfrac{5000}{500}=500

. The power gain is the product of the current gain and the voltage gain:

A_P=\beta A_V=50\times500=25000

. Equivalently

A_P=\beta^2\dfrac{R_{out}}{R_{in}}=2500\times10=25000

. A common slip is to quote the voltage gain

500

as the answer, or to use only

\beta^2=2500

and forget the resistance ratio.

Original question written in the JEE Main 2019 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake