Question

For a common base amplifier, current gain is $70$. If the emitter current is $8.8mA$, then the collector current is

• A. $0.124mA$
• B. $4.34mA$
• C. $8.68mA$
• D. $1.72mA$

Answer 1

The correct option is C $8.68mA$

Given:
$\beta =70$
$I_e=8.8mA$
Now,
$\alpha =\frac{\beta }{1+\beta }$

$\alpha =\frac{70}{1+70}$

$\alpha =\frac{70}{71}=0.9859$

For transistors:
$\alpha =\frac{I_c}{I_e}$
$\therefore I_c=\alpha I_e$
$\therefore I_c=\left(0.9859\right)\left(8.8\right)=8.675mA\approx 8.68mA$