The input resistance of a silicon transistor is 100 W. Base current is changed by 40 μA which results in a change in collector current by 2 mA. This transistor is used as a common emitter amplifier with a load resistance of 4KΩ. The voltage gain of the amplifier is

2000

Voltage gain $(A_V)=\frac{V_{out}}{V_{in}}=\frac{I_{out}}{I_{in}}×\frac{R_{out}}{R_{in}}$

$A_V=\frac{2×10^{-3}}{40×10^{-6}}×\frac{4×10^3}{100}=2×100=2000$