(b) Voltage gain $A_{v} = \frac{\mu}{1 + \frac{r_{p}}{R_{L}}}$ $\because R_{L} = 1.5r_{p} \Rightarrow A_{v} = \frac{\mu}{1 + \frac{r_{p}}{1.5r_{p}}} = \frac{3}{5}\mu = \frac{3}{5} \times 20 = 12$
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Ph.D. in Physics with 19+ years of teaching experience.