Snell's Law describes how light bends when crossing from one transparent medium to another: $n_1\sin {\theta }_1=n_2\sin {\theta }_2$

• $n_1,n_2$ are the absolute refractive indices of the media.
• ${\theta }_1$ is the angle of incidence and ${\theta }_2$ is the angle of refraction.
• When light enters a denser medium ($n_2>n_1$), it bends towards the normal (${\theta }_2<{\theta }_1$).