A ray of light falls on the surface of spherical glass (having refractive index n) making angle 30° with normal then net angle of deviation between emergent and incident rays is

$60^{\circ}-2 \sin ^{-1} \frac{1}{2 n}$

$\sin 30^{\circ}=n \sin r ; r=\sin ^{-1} \frac{1}{2 n}$

$\delta=30-r=30-\sin ^{-1} \frac{1}{2 n}$

$\delta_{net}=60-2 \sin ^{-1} \frac{1}{2 n}$