Refraction

When waves enter a new medium their speed changes as well as their angle.

If speed deceases, wavelength also does, while frequency stays constant.

We only need to draw the rays, no the wavefronts.

If the wave slows down, it bends towards the normal (e.g. when going from air into any material)

That means the angle of refraction is smaller than the angle of incidence.

Light disperses through a prism because different wavelengths are refracted different amounts (blue most, red least).

When the light exits, it speeds up again, and it bends away from the normal.