Question

A signal of $20\text{mV}$ is applied to common emitter transistor amplifier circuit. Due to this, the change in base current and the change in collector current are $20\mu \text{A}$ and $2\mu \text{A}$ respectively. The load resistance is $10\text{k}\Omega$. The voltage gain is,

• A. $1000$
• B. $100$
• C. $10$
• D. $0.01$

Answer 1

The correct option is A $1000$

Given:
Input signal, $V_{BE}=20\text{mV}=20\times {10}^{-3}\text{V}$

Change in base current, $\Delta I_B=20\mu \text{A}=20\times {10}^{-6}\text{A}$

Change in collector current, $\Delta I_C=2\text{mA}=2\times {10}^{-3}\text{A}$

Load/ output resistance, $r_o=10k\Omega =10\times {10}^3\Omega$

So, $r_o=\frac{\Delta V_{CE}}{{\Delta }_{I_C}}\Rightarrow 10\times {10}^3=\frac{\Delta V_{CE}}{2\times {10}^{-3}}$

$\Rightarrow \Delta V_{CE}=20\text{V}$

Further, voltage gain, $A_V=\frac{V_o}{V_i}=\frac{V_{CE}}{V_{BE}}=\frac{20}{20\times {10}^{-3}}=1000$

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

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