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 $70,68.6$

In common base mode $\alpha =0.98,R=5k\Omega ,R=70\Omega$

$\therefore$ voltage gain $A_v=\alpha \times \frac{R}{R_{in}}=0.98\times \frac{5\times {10}^3}{70}=70$

Power gain = Current gain $\times$ Voltage gain

$=0.98\times 70=68.6$