The current gain of a transistor in a common base arrangement is 0.95. Find the voltage gain if the load resistance of output circuit is \( 200\,\mathrm{k\Omega} \) and the input resistance is \( 200\,\Omega \).
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 950
In the common base arrangement the current gain is \( \alpha = I_C/I_E \). The output voltage is \( I_C R_L \) and the input voltage is \( I_E R_i \), so the voltage gain is the current gain times the resistance ratio.
\( \displaystyle A_V = \frac{I_C R_L}{I_E R_i} = \alpha\,\frac{R_L}{R_i} \)
\( \alpha = 0.95 \)
\( R_L = 200\,\mathrm{k\Omega} = 2\times10^{5}\,\Omega \)
\( R_i = 200\,\Omega \)
\( \displaystyle A_V = 0.95 \times \frac{2\times10^{5}}{200} = 0.95 \times 1000 = 950 \)