# Angle of the prism

**Classical Mechanics**Level 3

A parallel beam of light is incident from air at an angle \(\alpha\) on the side \(PQ\) of a right angled triangular prism of refractive index \(n = \sqrt{2}\). Light undergoes total internal reflection in the prism at the face PR when \(\alpha\) has a minimum value of \(45^{\circ}\). What is the angle \(\theta\) of the prism in degrees?