Refraction (Edexcel GCSE Physics)

Refraction

• Refraction can occur when a wave crosses a boundary between two materials with different densities

• In some cases, the wave will change direction

• The ray diagram below illustrates the change of direction of a light ray at a water-air boundary:

Waves can change direction when moving between materials with different densities

Refraction of light

• Refraction also occurs when light passes a boundary between two different transparent media

• At the boundary, the rays of light undergo a change in direction

• The direction is taken as the angle from the normal

• The change in direction depends on the difference in density between the two media:

  • From less dense to more dense (e.g air to glass), light bends towards the normal

  • From more dense to less dense (e.g. glass to air), light bends away from the normal

  • When passing along the normal (perpendicular) the light does not bend at all

Refraction of Light Through a Glass Block

Light enters the glass where the light ray bends towards the normal. Light bends away from the normal as it exits the glass 

• The change in direction occurs due to the change in speed when travelling in different substances

  • When light passes into a denser substance the rays will slow down, hence they bend towards the normal

• As with refraction of water waves, the only properties that change during refraction of light are speed and wavelength – the frequency of waves does not change

  • Different frequencies account for different colours of light (red has a low frequency, whilst blue has a high frequency)

  • When light refracts, it does not change colour (think of a pencil in a glass of water), therefore, the frequency does not change