Refraction of Waves

Refraction is the change in direction of a wave, at an interface between two media that creates a change in speed.

Water waves travel slower in shallow water than in deep. This is why waves break. The bottom of the waves slows down as the water becomes shallower up the beach. The top of the wave continues at its original speed and so 'falls' forward.

The water wave travels slower in the shallow water than in the deep. When a water wave enters shallow water at an angle to the interface (edge) it is bent the normal. When a water wave leaves a shallow water they bend the normal.

The same is true for light which also behaves as a wave. When light crosses an interface from a less optically dense to a more dense medium, it refracts the normal. When it crosses from a more optically dense to a optically dense medium, it is refracted the .

We have seen that the bigger the angle of incidence then the the ray is refracted (bent). This fact allows the design of lens that refract the light in specific ways, simply by changing the shapes of the lens.

The amount of refraction also depends on the frequency of light. If we bend the light in the same direction twice as in a 60° prism, then the combined colours of white light separate out as they are refracted by different amounts:

The colours that are refracted the least have the lowest frequencies (and the longest wavelengths). The colours in order are: , , , , , and .