A ray of light is incident normally on one of the faces of a prism of apex angle 30° and refractive index $\sqrt{2}$. The angle of deviation of the ray is

15°

Besides the formulae given for prism, we can always use the basic laws of refraction.

Using Snell’s law for the refraction at AC, we obtain

$\frac{\sin i}{\sin r}=\frac{n_2}{n_1}$

$⇒\frac{\sin 30°}{\sin r}=\frac{1}{\sqrt{2}}$

$⇒\sin r=1/\sqrt{2}$

⇒ r = 45°.

The angle of deviation, D = 45° - 30° = 15°