Question

In common emitter amplifier, the current gain is $62$. The collector resistance and input resistance are $5\text{k}\Omega$ and $500\Omega$ respectively. If the input voltage is $0.01\text{V}$, the output voltage will be

• A. $0.62\text{V}$
• B. $6.2\text{V}$
• C. $62\text{V}$
• D. $620\text{V}$

Answer 1

The correct option is B $6.2\text{V}$

Given:
Current gain, $\beta =62$

Collector resistance (output), $r_o=5k\Omega =5\times {10}^3\Omega$

Input resistance, $r_i=500\Omega$

Input voltage, $V_i=0.01\text{V}$

We know, voltage gain; $A_v=\beta \frac{r_o}{r_i}$

$\Rightarrow A_v=62\times \frac{5\times {10}^3}{500}=620$

Also, $A_v=\frac{V_o}{V_i}$

$\Rightarrow V_o=A_v\times V_i=620\times 0.01=6.2\text{V}$

Hence, $\left(B\right)$ is the correct answer.

$$\begin{array}{c}\text{Why this question?}\\ \text{Concept:- Voltage gain of common emitter amplifier is}\\ A_v=\frac{V_o}{V_i}=\beta \frac{r_o}{r_i}.\end{array}$$