sir i din understand the refractive index very well

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It is a measure of the extent to which radiation is refracted on passing through the interface between two media. Itis the ratio of the sine of the angle of incidence to the sine ofthe angle of refraction, which can be shown to be equal to theratio of the phase speed in the first medium to that in thesecond. In the case of electromagnetic radiation, esp light, it isusual to give values of the absolute refractive index  of amedium, that is for radiation entering the medium from free space

 

 

It is denoted by the symbol  and it is basically find as

 

Refractive index of a medium = 

 

More the refractive index lesser is the speed of light and more will be the bending of light towards the normal.