Question

A beam of light traveling in glass (n_g = 1.5) strikes a boundary with air (n_a = 1.0) at point P. The angle of incidence is 60° as shown in the diagram. Which ray would best indicate the beam’s path after point P?

A) A 

B) B 

C) C 

D) D 

E) E

Answer 1

The correct option is: (E) E

Explanation:

Generally when we go from more–less we should always check the critical angle first rather than assuming the ray will refract and bend away. Choice D might be correct, but not until we first check the critical angle for total internal reflection. Use ni sin θ_c = n_r sin (90), n_i =1.5, n_r =1 θ_c = 41.8°. Since our incoming angle (60) is larger than the critical angle, total internal reflection will occur and you will get choice E.