A common base amplifier has an input resistance $R_i=20\Omega$ and an output resistance $R_o=100\text{k}\Omega$. If the current gain $\alpha =0.98$, what is the power gain $A_p$ of the amplifier?

Solution

1. Given the current gain $\alpha =0.98$, input resistance $R_i=20\Omega$, and output resistance $$\begin{array}{rl}{R}_o& =100\text{k}\Omega \\ & =100,000\Omega \end{array}$$.
2. The power gain $A_p$ is defined by the formula $A_p={\alpha }^2\times \frac{R_o}{R_i}$.
3. Substituting the given values, $$\begin{array}{rl}{A}_p& =(0.98{)}^2\times \frac{100,000}{20}\\ & =0.9604\times 5,000\\ & =4,802\end{array}$$.
4. Rounding to the nearest provided option, we obtain $A_p\approx 4,900$.
5. Hence the answer is (A).