Question

A change of $8.0mA$ in the emitter current brings a change of $7.9mA$ in the current collector. The values of $\alpha$ and $\beta$ are :

• A. $0.99$, $90$
• B. $0.96$, $79$
• C. $0.97$, $99$
• D. $0.99$, $79$

Answer 1

The correct option is D $0.99$, $79$

Given that, change in emitter current,
$\Delta I_E=8mA$
and change in collector current,
$\Delta I_C=7.9mA$
We know that,
$\alpha =\frac{\Delta I_C}{\Delta I_E}\Rightarrow \alpha =\frac{7.9}{8}\Rightarrow \alpha \approx 0.99$
Also, we know that
$\beta =\frac{\alpha }{1-\alpha }\Rightarrow \beta =\frac{\frac{7.9}{8}}{1-\frac{7.9}{8}}$
$\Rightarrow \beta =\frac{7.9}{8-7.9}\Rightarrow \beta =\frac{7.9}{0.1}=79$
Hence, $\alpha =0.99$ and $\beta =79$.