Question

For a CE transistor amplifier, the audio signal voltage across the collector resistance of $2k$ omega is $4V$. If the current amplification factor of the transistor is $100$ and the base resistance is $1k$ Omega, then the input signal voltage is

• A. $10mV$
• B. $20mV$
• C. $30mV$
• D. $15mV$

Answer 1

The correct option is B

$20mV$

Step 1: Given

Amplification factor, $\frac{I_{\alpha }}{I_{\beta }}=100=\beta$

Resistance of the base, $R_B=1000\Omega$

Resistance of the collector, $R_L=2000\Omega$

Voltage across the collector resistance, $V_0=4V$

Step 2: Find the input signal voltage

Using the formula, $\frac{V_0}{V_i}=\beta \frac{R_L}{R_B}$

$$\begin{gathered} \frac{4}{V_i}=100\times \frac{2000}{1000} \\ \Rightarrow V_i=0.02V \\ =20mV \end{gathered}$$

Hence, option B is the correct option.