Question

In a common emitter transistor amplifier the audio signal voltage across the collector is 3 V. The resistance of collector is 3 kΩ. If current gain is 100 and the base resistance is 2 kΩ, the voltage and power gain of the amplifier is

• A. 200 and 1000
• B. 15 and 200
• C. 150 and 15000
• D. 20 and 2000

Answer 1

The Correct Option is C

 To find the voltage and power gain of a common emitter transistor amplifier, we need to understand the given parameters and use the appropriate formulae. The problem provides the following data:

• Audio signal voltage across the collector, \(V_c = 3\, \text{V}\)
• Collector resistance, \(R_c = 3\, \text{k}\Omega\)
• Current gain (β) = 100
• Base resistance, \(R_b = 2\, \text{k}\Omega\)

We are asked to find the voltage gain and power gain.

1. First, calculate the voltage gain (\(A_V\)):
   • The voltage gain of a common emitter amplifier is given by the formula:
   • \(A_V = \frac{V_c}{V_{in}}\)
   • The input voltage (\(V_{in}\)) can be found using the input resistance and current gain:
   • \(V_{in} = I_b \times R_b\), where \(I_b\) is the base current.
   • However, we need \(V_{in}\) in terms of the known collector values:
   • \(A_V = \beta \times \frac{R_c}{R_b}\)
   • Substituting the known values:
   • \(A_V = 100 \times \frac{3\, \text{k}\Omega}{2\, \text{k}\Omega} = 150\)
2. Next, calculate the power gain (\(A_P\)):
   • The power gain is given by:
   • \(A_P = A_V \times \beta\)
   • Substitute the voltage gain and current gain:
   • \(A_P = 150 \times 100 = 15000\)

Therefore, the voltage gain of the amplifier is 150, and the power gain is 15000.

The correct answer is:

150 and 15000