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Refraction is the change in the direction of a light ray when it travels from one medium to another.

A rectangular glass block is usually used to demonstrate the process of refraction. 

The ray which hit the glass surface is called the Incident Ray, the ray which bends on entering the glass block is called the Refracted Ray while the ray which comes out on the other side is called Emergent Ray. The ratio of the sine of the angle of incidence (i0) and the angle of refraction (ro) is called Refractive Index (n), therefore, 

Refractive Index = \( \frac {Refraction \; of \; light}{Refracted \; ray} \)

refraction of light
Refraction of light.

Refraction is also observed when light falls on smooth or curved surfaces. 

There are two types of curved surfaces made of glass called lenses, namely:

  • Convex or converging lenses: Convex lenses are thicker at the centre than at the edges.
  • Concave or diverging lenses: Concave lenses are thinner a the centre than at the edges.


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