A ray of light, incident on an equilateral prism (μg=√3) moves parallel to the base line of the prism inside it. Find the angle of incidence for this ray.

Since the ray of light moves parallel to the base inside the prism which is at an angle of 60° to the side of triangle where refraction took place, the angle of refraction is 30°. From Snell's law, sini = μg sinr = √3 sin30° = √3/2 ⇒ i = 60°