Question

The input resistance of common emitter transistor amplifier, if the output resistance is 500 k$\Omega$the current gain $\alpha = 0.98$ and the power gain is $6.0625 \times 10^{6}$ is

• A. $198\Omega$
• B. $300\Omega$
• C. $100\Omega$
• D. 400 $\Omega$

Answer 1

Answer: (A)

$198\Omega$

Answer 2

: Voltage gain$= A_{V} = \beta\frac{R_{o}}{R_{i}}$

Also, current gain $\beta = \frac{\alpha}{1 - \alpha} = \frac{0.98}{1 - 0.98} = 49$

$A_{V} = (49)\left( \frac{500 \times 10^{3}}{R_{i}} \right)$

Power gain = Current gain × voltage gain Power gain

$6.0625 \times 10^{6} = 49 \times \left( \frac{500 \times 10^{3}}{R_{i}} \right) \times 49$

Or $R_{i} = 198\Omega$