Question

The current gain of a transistor in a common emitter configuration is 80. The resistances in collector and base sides of the circuit are 5 k$\omega$ and 1 k$\omega$ respectively. If the input voltage is 2 mV, the output voltage is:

• A. \( 4V \)
• B. \( 0.4V \)
• C. \( 0.8V \)
• D. \( 8V \)

Hint:

For transistors, use the formula \( A_v = \beta \frac{R_C}{R_B} \) to determine voltage gain quickly.

Answer 1

The Correct Option is C

Step 1: The voltage gain \( A_v \) of a transistor in a common emitter configuration is given by: \[ A_v = \beta \times \frac{R_C}{R_B} \]
Step 2: Given: \[ \beta = 80, \quad R_C = 5k\Omega, \quad R_B = 1k\Omega \]
Step 3: Compute voltage gain: \[ A_v = 80 \times \frac{5}{1} = 400 \]
Step 4: Compute output voltage: \[ V_{\text{out}} = A_v \times V_{\text{in}} \] \[ V_{\text{out}} = 400 \times 2mV = 0.8V \]