Q: A ray of light is incident normally on one of the refracting surface of a prism of refracting angle A . The emergent ray grazes the other refracting surface. Find the refractive index of the material of prism.
Sol: For normal incidence on one of the refracting faces of the prism, i1 = 0 and r1 = 0.
But , r1 + r2 = A when light undergoes refraction through a prism.
0 + r2 = A; r2 = A
When the emergent light grazes the second surface, r2 becomes the critical angle (C)
i.e. C = A and μ = 1/sinC = 1/sinA