Refraction

What is refraction?

Refraction is the change in direction of a wave (typically light or sound) when it crosses a boundary between two media of different propagation speeds. Snell's Law quantifies it: n₁ sin θ₁ = n₂ sin θ₂, where n is the refractive index. Total internal reflection happens when light moves from a denser to less-dense medium and hits the boundary at or above the critical angle. A-Level Physics extends to fibre optics and thin-film interference.