Question

In a common emitter amplifier, the voltage gain and the current amplification factor are \(400\) and \(160\) respectively. If the output resistance of the amplifier is \(2500\,\Omega\), then its input resistance is

• A. \(1\,\text{k}\Omega\)
• B. \(6.25\,\text{k}\Omega\)
• C. \(1.25\,\text{k}\Omega\)
• D. \(2\,\text{k}\Omega\)

Hint:

For a transistor amplifier, \[ \boxed{ A_v=A_i\frac{R_o}{R_i}. } \] Thus, \[ \boxed{ R_i=\frac{A_iR_o}{A_v}. } \]

Answer 1

The Correct Option is A