Refraction of Light

Refraction of light is the bending of light ray when it enters a medium of a different density. When light enter a region of high density it will bend towards the normal. When light enter a region of lower density it will be away from the normal as demonstrated in the diagram below. When the light enter from the air to the glass which is of a higher density, it bends towards the normal. When it exit from the glass to the air which is of a lower density, it bends away. This bending of light is due to the different traveling speed of light in different medium.

Critical Angle 

There is a particular angle of incidence in which it will result in a total internal reflection. When this occurs, all the light will be reflected instead of be refracted. Every medium will have a different critical angle depending on the refractive index of the medium.

Laws of Refraction

First Law of Refraction

The incident ray, the normal and the refracted ray all lie in the same plane.

Second Law of Refraction (Snell's Law)

The ratio of the sine of the angle of incidence, i to the sine of the angle of refraction is constant.

Sin i / Sin r = n ,Constant; the refractive index of the medium.

The higher the refractive index, n, the more the bending of the light. The refractive index of a medium is also equal to the ratio of the speed of light in vacuum to the speed of light in medium.

Refractive Index = Speed of light in Vacuum / Speed of light in Medium

n = c / v 

Some daily common phenomena of refraction

There are some daily common phenomena of refraction which we would have observed. False perception of the depth of the swimming pool which make the depth of the pool seem shallower than it is. This can be very dangerous especially to young children. Secondly the bending of straw in a glass of water which make the straw seem bended. Last but not least, the mirage in the dessert which refract the images of objects from very far due to the different density in air.

Copyright 2008