Q. A transistor is used as an amplifier in $CB$ mode with a load resistance of 5 k $\Omega$. 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
Explanation
(a) Here, in $CB$ mode $\alpha = 0.98,$
$R =$5 k $\Omega = {5 \times 10}^{3}$
$R_{in} = 70\ \Omega$
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 $\times 70 = 68.6$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.