Question

The input resistance of a silicon transistor is $100\Omega$. Base current is changed by $40\mu A$ which results in a change in collector currently by $2mA$. This transistor is used as a common emitter amplifier with a load resistance of $4k\Omega$. The voltage gain of the amplifier is

• A. 2000
• B. 3000
• C. 4000
• D. 1000

Answer 1

Answer: (A)

Here,
Input resistance, $R_i=100\Omega$
Change in base current, $\Delta I_B=40\mu A$
Change in collector current, $\Delta I_C=2\mu A$
Load resistance, $R_L=4k\Omega =4\times 10^3\Omega$
Current gain, $\beta =\frac{\Delta I_C}{\Delta I_B}=\frac{2mA}{40\mu A}$
$=\frac{2\times 10^{-3}A}{40\times 10^{-6}A}=50$
Voltage gain of the amplifier is
$A_v=\beta \frac{R_L}{R_i}=50\times \frac{4\times 10^3}{100}=2000$