GCSE Physics Revision "Refraction of Waves"

Refraction is when waves change direction as they change speed, moving from one medium to another. This is demonstrated with two examples of light changing direction through water.

When light moves from air into a glass block, its velocity decreases, causing it to slow down and bend towards the normal. Conversely, when it moves from glass back to air, its velocity increases, causing it to speed up and bend away from the normal. An important exception is when waves enter or leave a medium along the normal, in which case they do not change direction.

For higher-tier students, wavefront diagrams explain refraction. A wavefront is an imaginary line connecting identical points (e.g., peaks) in a set of waves. When wavefronts move from air to glass, the parts entering the glass first slow down, causing the wavefronts to get closer and the wavelength to decrease, bending the waves towards the normal. If the whole wavefront slows down simultaneously, such as when approaching along the normal, the waves do not change direction.