• Refraction occurs when light passes a boundary between two different transparent media
• At the boundary, the rays of light undergo a?change in direction?and?a change in speed
• The change in direction is caused by the change in speed
  • Entering a?more dense?medium?slows?the light down and it bends?towards?the normal
    • In the denser medium there are more particles closer together providing more friction to the passing of the light through the material
  • Entering a?less?dense medium?speeds?the light up and it bends?away?from the normal
  • When passing?along the normal?(perpendicular) the light does?not?change speed?or?direction

Refraction of light through a glass block

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)
  • v?= 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)

   

Snell's Law

• Snell’s law relates the?angle of incidence?to the?angle of refraction, it is given by:

n1?sin?θ1?=?n2?sin?θ2

• Where:
  • n1?= the refractive index of material 1
  • n2?= the refractive index of material 2
  • θ1?= the angle of incidence of the ray in material 1 (°)
  • θ2?= the angle of refraction of the ray in material 2 (°)

   

Snell's Law is used to find the refractive indices or the angles to the normal at a boundary

• θ1?and?θ2?are always taken from the?normal
• Material 1 is always the material in which the ray goes through?first
• Material 2 is always the material in which the ray goes through?second