Refraction of waves
Waves transmitted at the interface (boundary) between two materials may change direction. Refraction is the change in direction of a wave at such a boundary. All wave types can be refracted.
It is important to be able to draw ray diagrams to show the refraction of a wave at a boundary.
Explaining refraction - Higher
The density of a material is one of the factors that affects the speed that a wave will be transmitted through it.
A useful way of remembering the speed and direction changes of waves during refraction is 'FAST': Faster - Away / Slower - Towards