## Refraction

The speed at which a wave travels is dependant upon the medium in which it travels along or through. The speed of a wave changes when a wave moves from one medium to another. This change in wave speed is accompanied by a change in wavelength and change in direction. It is this change of direction or bending of the wave as it passes from one medium to another that is called refraction.

### Effects of Refraction

Refraction is why water appears shallower than it really is. In the diagram below the rays of light from the fish are refracted away from the normal as the leave the water. This bending of the light is not registered by the eye rather it seems as if the rays come from an imaginary fish higher in the fish bowl. Therefore the apparent position of the fish is higher than the real position.

Important to Remember!
• The speed of a wave is affected by the medium in which the wave is travelling through or along.
• A change in wave speed causes a change in wavelength as the frequency cannot change.
• The normal line is an imaginary construction line at right angles (perpendicular) to the refracting or reflecting surface at the point of incidence.
• When light waves travel into a denser medium the waves are refracted towards the normal and on leaving the denser medium are refracted away from the medium. This is because light travels slower in the denser medium.
• When sound waves travel into a denser medium the waves are refracted away from the normal and on leaving the denser medium are refracted towards the medium. This is because sound waves travel faster in a denser medium.