Question

For a common emitter amplifier, current gain is $60$. If the emitter current is $6.6mA$, the base current is

• A. $1.08mA$
• B. $10.8mA$
• C. $0.108mA$
• D. $8.01mA$

Answer 1

Answer: (C)

$0.108mA$

Given that:
$\beta =60$
$I_e=6.6mA$
For transistors,
$\alpha =\frac{\beta }{1+\beta }$

$\alpha =\frac{60}{1+60}=\frac{60}{61}=0.9836$

Also,
$\alpha =\frac{I_c}{I_e}$

$I_c=\alpha I_c=\left(0.9836\right)\left(6.6\right)=6.49176\approx 6.492mA$
Now,
$I_e=I_b+I_c$
$I_b=I_e-I_c$
$I_b=6.6-6.492=0.108mA$