Question

In common emitter transistor amplifier, the output resistance is \(500\) k\(\Omega\) and the current gain \(β = 50\). If power gain of amplifier is \(5\times 10^6\), what is the input resistance?

• A. \(325\Omega\)
• B. \(150\Omega\)
• C. \(350\Omega\)
• D. \(250\Omega\)

Hint:

Power gain $=\beta^2\frac{R_{out}}{R_{in}}$.

Answer 1

The Correct Option is D

Step 1: Formula
In a common emitter amplifier, power gain \(=\beta^2\times\frac{R_{out}}{R_{in}}\).

Step 2: Substitute
\(5\times10^6=2500\times\frac{5\times10^5}{R_{in}}\).

Step 3: Solve
\(R_{in}=\frac{2500\times5\times10^5}{5\times10^6}=250\,\Omega\). Option (D).

Final Answer:
The input resistance is \(250\,\Omega\), option (D). \[ \boxed{\text{(D) }250\,\Omega} \]