What is the angle θ of the prism?
Here is my diagram: https://i.stack.imgur.com/WYSnE.png
A parallel beam of light is incident from air at an angle a on the side PQ of a right angled triangular prism of refractive index n=√2. Light undergoes total internal reflection in the prism at the face PR when a has a minimum value of 45°. What is the angle θ of the prism?
I'm a bit confused right now. However, I think that we need to use Snell's law.