Question

For normal incidennce at the air dielectric interface with dielectri constant Er=4. Find the fraction of energy reflected into the air?

Answer 1

$$R=\left(\frac{n_1-n_2}{n_1+n_2}\right)^2$$

$$n_1=1, n_2=\sqrt{E_r}=2$$

$$R=\left(\frac{1-2}{1+2}\right)^2=\frac{1}{9}$$