A ray of light is travelling from glass to air. (Refractive index of glass $=1.5$). The angle of incidence is ${50}^o$.The deviation of the ray is

The correct option is B 80${}^o$
${}^a{\mu }_g=1.5$

$\therefore 1.5=cosecC$

Or, $C={42}^0$.

Critical angle for glass $={42}^0$. Hence a ray of light incident at ${50}^0$ in glass medium undergoes total internal reflection. $\delta$ denotes the deviation of the ray.

$\delta ={180}^o-({50}^o+{50}^o)$ or $\delta ={80}^o$.