Question

What is the current gain for a transistor used as common emitter amplifier, if the current gain of the common base $\text{n-p-n}$ transistor is $0.96$ ?

• A. $16$
• B. $24$
• C. $20$
• D. $32$

Answer 1

The correct option is B $24$

Given:
Current gain of the common base $\text{n-p-n}$ transistor $\alpha =0.96$
Current gain of the common emitter, $\beta =?$
We know, $\alpha =\frac{\beta }{1+\beta }\text{or}\beta =\frac{\alpha }{1-\alpha }$
$\Rightarrow \beta =\frac{0.96}{1-0.96}=24$

$\begin{array}{c}\text{Why this question?}\\ \text{Concept: Relation between current gain of common base and common emitter is}\alpha =\frac{\beta }{1+\beta }\text{or}\beta =\frac{\alpha }{1-\alpha }\end{array}$