Refractive index
Snell's law turns into a number you can calculate: the refractive index, n.
Refractive index
n = sin i ÷ sin r
the sine of the angle of incidence divided by the sine of the angle of refraction
For a ray going from air into glass the refractive index is written ang; from glass into air, gna.
| Relative to air | Refractive index |
|---|---|
| Water | anw = 1.33 |
| Glass | ang = 1.5 |
An example
Problem
A ray passes from air into glass. The angle of incidence is 30° and the angle of refraction is 19.5°. Find the refractive index of the glass. (sin 30° = 0.5, sin 19.5° = 0.334)
Solution
n = sin i ÷ sin r
= 0.5 ÷ 0.334
= 1.5
Refractive index is a ratio of two sines, so it has no unit.