Question

For a common emitter amplifier, the current gain is $70$. If the emitter current is $8.8$ mA, 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 that:
$\beta =70$
$I_e=8.8mA$
For transistors:
$\alpha =\frac{\beta }{1+\beta }$
$\alpha =\frac{70}{1+70}=\frac{70}{71}=0.986$
Also,
$\alpha =\frac{I_c}{I_e}$
$I_c=\alpha I_e=\left(0.986\right)\left(8.8\right)=8.6768\approx 8.68mA$