Refraction of Light

When light travels from one transparent medium to another, it changes direction at the boundary. This is called refraction.

Snell's Law

$$n_1 \sin \theta_1 = n_2 \sin \theta_2$$

The refractive index of medium 2 with respect to medium 1:

$$n_{21} = \frac{n_2}{n_1} = \frac{\sin \theta_1}{\sin \theta_2}$$

Refractive Index and Speed of Light

$$n = \frac{c}{v}$$

where $c = 3 \times 10^8 \, \text{m/s}$ is the speed of light in vacuum and $v$ is the speed in the medium.