Question

In a CE transistor amplifier, the audio signal voltage across the collector resistance of \(2\,\text{k}\Omega\) is \(2\,\text{V}\). If the base resistance is \(1\,\text{k}\Omega\) and the current amplification of the transistor is \(100\), the input signal voltage is:

• A. \(2\,\text{mV}\)
• B. \(3\,\text{mV}\)
• C. \(10\,\text{mV}\)
• D. \(0.1\,\text{mV}\)

Hint:

For CE amplifier: \[ V_{out}=I_cR_c,\quad I_c=\beta I_b \] Work backward from output.

Answer 1

The Correct Option is A

Step 1: Collector current: \[ I_c = \frac{2}{2000} = 1\,\text{mA} \]
Step 2: Base current: \[ I_b = \frac{I_c}{\beta} = \frac{1\,\text{mA}}{100} = 10\,\mu\text{A} \]
Step 3: Input voltage: \[ V_{in} = I_b R_b = 10\,\mu\text{A} \times 1000 = 2\,\text{mV} \]