- Created by: mtgriffiths
- Created on: 14-03-16 17:54
What is Refractive Index and How to Calculate it?
Refractive Index: The ratio between the speed of light in a vacuum and the speed of light in material.
n = c / cs
n = refractive index of the material
c = 3.0 x 10^8
cs = speed of light in material in ms^-1
n of air is only slightly smaller than c so is treated as = 1
The Law of Refraction - Part 1
- The angle of the incoming light to the normal is theta 1, called the angle of incidence.
- The angle of the refracted ray to the normal is theta 2, called the angle of refraction.
n1 x sin(theta 1) = n2 x sin(theta 2)
n1 = refractive index of material 1
theta 1 = angle of incidence of ray of material 1
n2 = refractive index of material 2
theta 2 = angle of refraction of ray of material 2
Law of Refraction - Part 2
As light moves across a boundary between two different materials of different optical densities, its direction changes because of its change in speed.
The direction can change in two ways:
- Towards the normal, if it passes from a less optically dense material into a more optically dense material. E.g. if n1 < n2 then theta 1 > theta 2
- Away from the normal, if it passes from a more optically dense material into a less optically dense material. E.g. if n1 > n2 then theta 1 < theta 2