• Refraction 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 a hypothetical line called the normal
  • This line is perpendicular to the surface of the boundaries and is represented by a straight dotted line

   

• The change in direction depends on which media the light rays pass between:
  • From air to glass (less dense to more dense): light bends?towards?the normal
  • From glass to air (more dense to less dense): 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

• 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

   

• The only properties that change during refraction are speed and wavelength – the frequency of waves?does not change
  • Technically the intensity and amplitude of the wave also decreases slightly upon refraction since a small portion of the wave also reflects but this is not as noticeable as the change in speed and wavelength

   

Calculating Refractive Index

• The refractive index,?n, is a property of a material which measures how much light slows down when passing through it

• • Where:
    • c?=?the speed of light?in a vacuum (m s–1)
    • cs?= the speed of light in a substance (m s–1)

     

• Light travels at different speeds within different substances depending on their refractive index
  • A material with a high refractive index is called?optically dense, such material causes light to travel?slower

   

• Since the speed of light in a substance will always be less than the speed of light in a vacuum, the value of the n is?always greater than 1
• In calculations, the refractive index of air can be taken to be approximately?1
  • This is because light does not slow down significantly when travelling through air (as opposed to travelling through a vacuum)