Question

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

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

Answer 1

The Correct Option is C

Given : Voltage across the collector $V_{0}=2 V$;
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 $\alpha=\frac{I_{C}}{I_{B}}=100$
$\Rightarrow I_{B}=\frac{I_{C}}{100}=\frac{10^{-3}}{100}$
$=10^{-5} A V_{i}=R_{B} I_{B}$
$\Rightarrow V_{i} 1$
$\times 10^{3} \times 10^{-5}$
$\Rightarrow V_{i}=10^{-2} V$
$\Rightarrow V_{i}=10\, m V$