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 $2 \, mA$. This transistor is used as a common emitter amplifier with a load resistance of $4 \,k \Omega$. 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, $R_L=4 k\Omega =4\times 10^3 \Omega$
Current gain, $\beta=\frac{\Delta I_C}{\Delta I_B}=\frac{2 mA}{40 \mu A}$
$=\frac{2\times 10^{-3} A}{40\times 10^{-6} A}=50$
Voltage gain of the amplifier is
$A_v=\beta\frac{R_L}{R_i}=50\times\frac{4\times 10^3}{100}=2000$