Refractive index

The refractive index tells you the speed at which light will pass through a specific material:

• A higher refractive index means the light moves more slowly
  • During refraction, it will bend towards the normal.
• A lower refractive index means the light moves more quickly
  • During refraction, it will bend away from the normal.

Calculating the refractive index

If we have a material which has a refractive index of n, and light travels through it at a speed c_s, we can represent this relationship with this equation:

n=\frac c{c_s}

• n is the refractive index of the material - it has no unit because it’s a ratio.
• c is the speed of light in a vacuum - measured in ms^{-1}
• c_s is the speed of light through the material - measured in ms^{-1}