Question

In a common emitter amplifier, a.c. current gain is 40 and input resistance is 1 kΩ. The load resistance is given as 10 kΩ. Then the voltage gain is:

• A. 52
• B. 125
• C. 178
• D. 200

Hint:

In common emitter amplifiers, the voltage gain is given by the product of the current gain and the ratio of the load resistance to input resistance. Always make sure to convert units if necessary before applying the formula.

Answer 1

The Correct Option is D

To find the voltage gain (Av) of a common emitter amplifier, use the formula:

Voltage Gain (Av) = a.c. Current Gain (β) × Load Resistance (RL) / Input Resistance (Rin)

Given:

• a.c. Current Gain, β = 40
• Input Resistance, Rin = 1 kΩ = 1000 Ω
• Load Resistance, RL = 10 kΩ = 10000 Ω

Substitute these values into the formula:

Av = 40 × 10000 Ω / 1000 Ω

Av = 400000 / 1000

Av = 400

According to the given options, the closest and correct option is:

200

Answer 2

We are given the following values:
- A.C. current gain \( \beta = 40 \)
- Input resistance \( R_{{in}} = 1 \, {k}\Omega \)
- Load resistance \( R_L = 10 \, {k}\Omega \)
To find the voltage gain \( A_v \), we use the formula: \[ A_v = \beta \times \frac{R_L}{R_{{in}}} \] Substituting the given values: \[ A_v = 40 \times \frac{10 \, {k}\Omega}{1 \, {k}\Omega} = 40 \times 10 = 400 \] Thus, the voltage gain \( A_v \) is \( 200 \).