Question

For a common-emitter amplifier, the voltage gain is $40$. Its input and output impedances are $100\ \Omega$ and $400\ \Omega$, respectively. The power gain of the CE amplifier will be

• A. 450
• B. 400
• C. 300
• D. 500

Hint:

To solve this quickly, memorize the unified formula: $\text{Power Gain} = \frac{A_v^2 \times Z_i}{Z_o}$. Substituting the values directly gives $\frac{1600 \times 100}{400} = \frac{1600}{4} = 400$. This layout avoids splitting the calculation into two separate stages!

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
For a CE amplifier with voltage gain A_v=40, input impedance Z_i=100Ω, output impedance Z_o=400Ω, find the power gain A_p.

Step 2: Key Formula or Approach:
Power gain A_p = A_v × A_i, and current gain A_i = A_v × (Z_i/Z_o).

Step 3: Detailed Explanation:
A_i = 40 × (100/400) = 10. Then A_p = 40 × 10 = 400.

Step 4: Final Answer:
Power gain is 400, matching option (B).