Question

A transistor is used as a common emitter amplifier with a load resistance 2 K$\Omega$. the input resistance is 150 $\Omega$. Base current is changed by 20 $\mu$A which results in a change in collector current by $1.5\, mA$. The voltage gain of the amplifier is

• A. 900
• B. 1000
• C. 1100
• D. 1200

Answer 1

Answer: (B)

1000

Answer 2

Given, load resistance $\left(R_{e}\right)=2 k \Omega=2 \times 10^{3} \Omega$
Input resistance $\left(R_{i}\right)=150 \Omega$
Change in collector current $\left(\Delta I_{C}\right)=1.5\, mA$
$=1.5 \times 10^{-3} A$
Change in base current $\left(\Delta I_{B}\right)=20 \mu A =20 \times 10^{-6} A$
We know that,
$\text { voltage gain } =\frac{V_{0}}{V_{i}}=\frac{R_{0} \times \Delta I_{C}}{R_{i} \times \Delta I_{B}}$
$=\frac{2 \times 10^{3} \times 1.5 \times 10^{-3}}{150 \times 20 \times 10^{-6}}=\frac{3 \times 10^{6}}{150 \times 20}$
$= 1000$