THE LAW OF REFRACTION

The law of refraction is generally written today as

n1sin 1 = n2sin 2, or sin 1/sin 2 = n2/n1 = k

1 is the angle of incidence of the light ray in medium 1, say air, and 2 is the angle of refraction from the air into medium 2, which might be glass or water, or any other transparent medium besides air. The number n1 is called the “index of refraction” of medium 1 with respect to a vacuum, and similarly for n2. The index of refraction of a vacuum is defined to be 1, and k is the index of refraction for medium 2 with respect to medium 1.

Clearly the angles 1 and 2 will vary as the light rays approach from different directions, but the amazing thing about the law of refraction is that for any two given media, sin 1/ sin 2 is constant.