Question

In $CE$ transistor amplifier, the audio signal voltage across the collector resistance of $2k\Omega$ is $2V$. If the base resistance is $1k\Omega$ and the current amplification of the transistor is $100$, the input signal voltage is

• A. $2mV$
• B. $3mV$
• C. $10mV$
• D. $0.1mV$

Answer 1

Answer: (C)

$10mV$

Given : Voltage across the collector $V_0=2V$; collector resistance, $R_c=2\times {10}^3\Omega$; Base resistance $R_B=1\times {10}^3\Omega$; Input signal voltage, $V_i=?$
$V_0=I_C{R}_C=2$
$\Rightarrow I_C=\frac{2}{2\times {10}^3}={10}^{-3}A$
Current gain $\alpha =\frac{I_C}{I_B}=100$
$\Rightarrow I_B=\frac{I_C}{100}=\frac{{10}^{-3}}{100}={10}^{-5}A$
$V_i=R_B{I}_B\Rightarrow V_i=1\times {10}^3\times {10}^{-5}$
$\Rightarrow V_i={10}^{-2}V\Rightarrow V_i=10mV$.