Question

A uniform plane wave travelling in air is incident on the plane boundary between air and another dielectric medium with ${ϵ}_r=4$. The reflection coefficient for electric field at normal incidence, is

Answer 1

Ans : (d)

$\Gamma =\frac{{\eta }_2-{\eta }_1}{{\eta }_2+{\eta }_1}$

$=\frac{\sqrt{\frac{{\mu }_0}{{ϵ}_0{ϵ}_r}}-\sqrt{\frac{{\mu }_0}{{ϵ}_0}}}{\sqrt{\frac{{\mu }_0}{{ϵ}_0{ϵ}_r}}+\sqrt{\frac{{\mu }_0}{{ϵ}_0}}}=\frac{\frac{1}{\sqrt{{ϵ}_r}}-1}{\frac{1}{\sqrt{{ϵ}_r}}+1},{ϵ}_r=4$



$\frac{-1/2}{3/2}=\frac{-1}{3}\Rightarrow 0.333\angle {180}^{\circ }$