Question

A uniform plane wave travelling in air is incident on the plane boundary between air and another dielectric medium with εr = 4. The reflection coefficient for the normal incidence is

Answer 1

In general we have

$n = \sqrt{\epsilon_r \mu_r}$

For dielectric medium we can suppose $\mu_r \approx 1$ and thus $n =\sqrt{\epsilon_r}$ .

Therefore we have $\rho = \frac{(n-1)^2}{(n+1)^2}=\frac{1}{9}$ .