We met refraction during the National 5 course. At Higher level, we are interested in the relationship between the angles of incidence (θi) and refraction (θr).

Snell’s law tells us that

Usually material 1 is air, and so . This simplifies Snell’s law to

where n is the *absolute refractive index* of material 2. Since the refractive index is equal to the ratio of the ray’s speed (v) in materials 1 & 2 and also equal to the ratio of the wave’s wavelength (λ) in materials 1 & 2, we can show that

Read more about Snells’s law here.

### total internal reflection

The critical angle and refractive index n are related by

Here are some applications of total internal reflection here. You can test your knowledge of refraction with this interactive simulation.

I have attached a pdf with some notes and questions on refraction, total internal reflection and critical angle.