Question

For a common emitter amplifier, the audio signal voltage across the collector resistance of $2000\Omega \text{is}2\text{V}$. If the current amplification of the transistor is $200$ and the base resistance is $1500\Omega$, the input signal voltage and base current are

• A. $0.015\text{V}\text{and}1\text{A}$
• B. $0.15\text{V}\text{and}10\mu \text{A}$
• C. $0.0075\text{V}\text{and}5\mu \text{A}$
• D. $0.1\text{V}\text{and}1\mu \text{A}$

Answer 1

The correct option is C $0.0075\text{V}\text{and}5\mu \text{A}$

Here,
$V_0=2\text{V}$
$R_C=2000\Omega ,R_B=1500\Omega$
$\beta =200$

The voltage gain is,

$A_V=\frac{V_0}{V_1}=\beta \frac{R_C}{R_B}\Rightarrow V_1=\frac{V_0{R}_B}{\beta R_C}$

Substituting the values, we get,

$V_1=\frac{2\times 1500}{200\times 2000}=0.0075\text{V}$

$I_C=\frac{V_0}{R_C}=\frac{2}{2000}=1\text{mA}$

Also,
$\beta =\frac{I_C}{I_B}\Rightarrow I_B=\frac{I_C}{200}=\frac{1\times {10}^{-3}}{200}$

$\Rightarrow I_B=5\times {10}^{-6}\text{A}=5\mu \text{A}$.

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