8. If the index of refraction for a certain glass is 1.50, and the angle of refraction is 15° for a ray of
light traveling from air, what is the angle of incidence?

Approximately .

Explanation:

Let

be the angle of incidence, and be the angle of refraction.

By Snell's Law, ,

where

is the refractive index of the medium where the light comes from, and is the refractive index of the medium that the light enters.

In this case,

The light initially travels in the air. The refractive index of the air is approximately (about the same as that of vacuum.) Hence, .The light enters into glass, which (according to the question) has a refractive index of . That is: .

Also, the question states that the angle of refraction is . By Snell's Law,

.

Solve for , the angle of incidence.

.

.

Hence, the angle of incidence is approximately .