Question

The input resistance of a silicon transistor is $665\Omega$. Its base current is changed by $15\mu A$ which results in the change in collector current by $2mA$. This transistor is used as a common emitter amplifier with a load resistance of $5k\Omega$. What is the voltage gain of the amplifier?

• A. 1002.5
• B. 1232.8
• C. 7235.9
• D. 9879.3

Answer 1

Answer: (A)

$R_i=665\Omega ,\Delta I_B=15\mu A=15\times 10^{-6}A$
$\Delta I_C=2mA=2\times 10^{-3}A,R_L=5k\Omega =5\times 10^3\Omega$
$\beta =\frac{\Delta I_C}{\Delta I_B}=\frac{2\times 10^{-3}}{15\times 10^{-6}}=\frac{400}{3}$
Voltage gain, $A_V=\beta .\frac{R_L}{R_i}$
$A_V=\frac{400}{3}\times \frac{5\times 10^3}{665}=1002.5$