Question

In common emitter amplifier, current gain is 80 and emitter current is 9 mA. the base current is ____ . correct answer ​

Answer 1

Answer:

Answer of the question is 81

Answer 2

Given,

A common emitter amplifier with,

Current gain, $\beta =80$

Emitter current, $I_{e}=9mA$

To find,

The value of base current, $I_{b}$.

Solution,

We know that,

For transistors,

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

Where, $\alpha$ is the ratio of the collector current to the emitter current.

⇒$\alpha =\frac{80}{1+80}$

⇒$\alpha =\frac{80}{81}$

⇒$\alpha =0.987$

And also,

$\alpha =\frac{I_{c}}{I_{e}}$

Where, $I_{c}$ is the collector current.

⇒$I_{c}=\alpha .I_{e}$

⇒$I_{c}=0.987$×$9$

⇒$I_{c}=8.88A$

And we know that,

The current flowing through the resistor is the sum of base current, $I_{b}$ and collect current, $I_{c}$.

⇒$I_{e}=I_{c}+I_{b}$

So,

Putting the values of respective currents in the equation, we get

⇒$I_{b}=I_{e}-I_{c}$

⇒$I_{b}=9-8.88$

⇒$I_{b}=0.12mA$

Therefore, the value of the base current $I_{b}=0.12mA$.