Question

A transistor is used as an amplifier in $CB-$ mode with a load resistance of $5k\Omega$ the current gain of amplifier is $0.98$ and the input resistance is $70\Omega .$ The voltage gain and power gain respectively are

• A. $70;68.6$
• B. $80;75.6$
• C. $60;66.6$
• D. $90;96.6$

Answer 1

The correct option is A $70;68.6$

Given:

$\alpha =0.98;R_L=5k\Omega ;R_{in}=70\Omega$

$\alpha =\frac{I_C}{I_E}=0.98$

Voltage gain is,

$A_V=\alpha \frac{R_L}{R_{in}}=0.98\times \frac{5\times {10}^3}{70}=70$

Power gain is,

$A_P=A_V\times \alpha ={\alpha }^2\frac{R_L}{R_{in}}=(0.98{)}^2\times \frac{5\times {10}^3}{70}=68.6$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(A\right)$ is the correct answer.