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: Formula for power gain.
In a common emitter transistor, the power gain \( P_{\text{gain}} \) is given by the product of current gain \( \beta \) and voltage gain \( A_v \):
\[ P_{\text{gain}} = \beta \cdot A_v. \]
We are given that the current gain \( \beta = 8 \).

Step 2: Formula for voltage gain.
The voltage gain \( A_v \) is the ratio of the load resistance \( R_L \) to the input resistance \( R_{\text{in}} \):
\[ A_v = \frac{R_L}{R_{\text{in}}}. \]
We are given that \( R_L = 75kΩ \) and \( R_{\text{in}} = 25kΩ \), so:
\[ A_v = \frac{75kΩ}{25kΩ} = 3. \]

Step 3: Calculating power gain.
Now, we can calculate the power gain:
\[ P_{\text{gain}} = \beta \cdot A_v = 8 \cdot 3 = 24. \]

Step 4: Final Answer.
Thus, the power gain is \( \boxed{224} \).