Question

In common emitter mode of a transistor, the current gain is 8. The input impedance is 25kΩ and load resistance is 75kΩ. The power gain is

• A. 192
• B. 112
• C. 316
• D. 224

Hint:

In a transistor amplifier, the power gain is the product of the current gain and the voltage gain. Voltage gain is the ratio of the load resistance to the input resistance.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
Power gain in a transistor amplifier is the product of voltage gain and current gain.
Step 2: Key Formula or Approach:
1. Voltage Gain \( A_v = \beta \cdot \frac{R_L}{R_{in}} \).
2. Power Gain \( P_g = \text{Current Gain} \times \text{Voltage Gain} = \beta^2 \cdot \frac{R_L}{R_{in}} \).
Step 3: Detailed Explanation:
Given: \( \beta = 8 \), \( R_{in} = 25\text{k}\Omega \), \( R_L = 75\text{k}\Omega \).
Voltage Gain:
\[ A_v = 8 \cdot \left( \frac{75}{25} \right) = 8 \cdot 3 = 24 \]
Power Gain:
\[ P_g = \beta \cdot A_v = 8 \cdot 24 = 192 \]
Alternatively:
\[ P_g = 8^2 \cdot \left( \frac{75}{25} \right) = 64 \cdot 3 = 192 \]
Step 4: Final Answer:
The power gain is 192.