Physics - Semiconductors Question with Solution | TestHub

The voltage gain $A_v$ of a transistor in common emitter configuration is the ratio of output voltage to input voltage.

$A_v=\frac{V_{out}}{V_{in}}=\frac{I_c{R}_L}{I_{b}r}$

Since the a.c. current gain is $\beta =\frac{I_c}{I_b}$, we get:

$A_v=\beta \left(\frac{R_L}{r}\right)$

The power gain $A_p$ is the ratio of output power to input power.

$A_p=\frac{P_{out}}{P_{in}}=\frac{I_c^2{R}_L}{I_b^{2}r}={\left(\frac{I_c}{I_b}\right)}^2\left(\frac{R_L}{r}\right)$

$A_p={\beta }^2\left(\frac{R_L}{r}\right)$

Answer: $\beta (R_L/r)$ and ${\beta }^2(R_L/r)$