Question

The critical angle for two media of refractive indices of medium 1 and 2 given by 2 and 1 respectively is

(a) 0

(b) 30

(c) 45

(d) 60

This question was addressed to me in an online quiz.

My question is taken from Snell Law and Critical Angle topic in section EM Wave Propagation of Electromagnetic Theory

Answer 1

Correct option is (b) 30

The explanation is: The sine of the critical angle is the ratio of refractive index of medium 2 to that in medium 1. Thus sin θc = n2/n1. To get θc, put n1 = 2 and n2 = 1. Thus we get θc = sin^-1(n2/n1) = sin^-1(1/2) = 30 degree.