Question

A ray of light travelling through air, falls on the surface of a glass slab at an angle $i$. It is found that the angle between the reflected and refracted ray is ${90}^o$. If the speed of light in glass is $2\times {10}^{8}m/s$, find the angle of incidence. (c = $3\times {10}^{8}m/s$)

Answer 1

Since, $\mu =\frac{speedoflightinvacuum}{speedoflightinmedium}$

${\mu }_g=\frac{3\times {10}^8}{2\times {10}^8}=1.5$

$r=90-i$

Hence from Snell's law,

${\mu }_{1}sini={\mu }_{2}sinr$

$1sini=\frac{3}{2}sin(90-i)$

$tani=\frac{3}{2}$

$i={tan}^{-1}\left(3/2\right)=56.30$