Wave Behaviour & Superposition

Refraction and total internal reflection

When light enters a denser medium it slows and bends towards the normal. The refractive index $n=\frac{c}{v}$, and Snell's law: $$n_1\sin\theta_1 = n_2\sin\theta_2$$ Beyond the critical angle ($\sin\theta_c = \frac{1}{n}$ for a medium to air), light undergoes total internal reflection — the basis of optical fibres.