Question

The critical angle for two media with permittivities of 16 and 9 respectively is

(a) 48.59

(b) 54.34

(c) 60

(d) 45

This question was addressed to me in class test.

My doubt stems from Snell Law and Critical Angle in section EM Wave Propagation of Electromagnetic Theory

Answer 1

Correct option is (a) 48.59

To elaborate: 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. Also n = √ε, thus sin θc = √ε2/√ε1. Put ε1 = 16 and ε2 = 9, we get θc = sin^-1(3/4) = 48.59 degree.