Question

For a CE transistor amplifier, the audio signal voltage across the collector resistance of \( 4 \, \text{k}\Omega \) is 5V. If the current amplification factor of the transistor is 100 and the base resistance is \( 2 \, \text{k}\Omega \), then the input signal voltage is

Hint:

In transistor amplifier problems, use the voltage amplification formula to relate the input and output voltages, and solve for the unknown.

Answer 1

The voltage amplification \( A_v \) for a CE transistor amplifier is given by: \[ A_v = \frac{V_{\text{out}}}{V_{\text{in}}} = \beta \cdot \frac{R_{\text{out}}}{R_{\text{in}}} \] Given: - \( V_{\text{out}} = 5 \, \text{V} \), - \( R_{\text{out}} = 4 \, \text{k}\Omega \), - \( R_{\text{in}} = 2 \, \text{k}\Omega \), - \( \beta = 100 \). Using the formula: \[ A_v = \frac{5}{V_{\text{in}}} = 100 \cdot \frac{4 \, \text{k}\Omega}{2 \, \text{k}\Omega} = 200 \] Now, solving for \( V_{\text{in}} \): \[ V_{\text{in}} = \frac{5}{200} = 0.025 \, \text{V} = 25 \, \text{mV} \] Thus, the correct answer is (B).