A layer of ethyl alcohol (n = 1.361) is on top of water (n = 1.333). To the nearest degree, at what angle relative to the normal to the interface of the two liquids is light totally reflected?
A) 78°
B) 88°
C) 68°
D) 49°
E) the critical angle is undefined

Question

Quizplus · Accepted Answer

The critical angle is given by sin(theta_c) = n2/n1, where n1 is the index of refraction of the less dense medium and n2 is the index of refraction of the denser medium. In this case, n1 = 1.333 and n2 = 1.361, so sin(theta_c) = 1.333/1.361 = 0.979. Therefore, theta_c = 78 degrees.

A Layer of Ethyl Alcohol (N = 1