Question

What is refractive index????????

Answer 1

           The light propagates through the medium. Whether, it is solid, liquid or gas. The number which describes or provides data that how light propagates through the medium is called as Refractive Index. This refractive index is a Dimension less number. The refractive index remain dimensionless because this number is a ratio of the velocity of the light, in a vaccum. Where, even the air is not in existence. This ratio presents the velocity of light to the velocity of medium.

           When the light ray passes through one medium to the another medium, it bends. This refractive index shows this bending. We can say refractive index as index of refraction. It is the reduction of velocity of light in that medium. i.e. solid, liquid or gas. Let me tell you the symbolized form of this refractive index or index of refraction.

          The refractive index is generally and most commonly presented it's variables by the n or n' (pronouncemental n-dash) in mathematical equations. The snell's law for this refractive index or index of refraction named 'indices of refraction', states that n of any two media to the direction of propagation, always angles to the normal.

        We can do show the refractive index or index of refraction by the n = c/v , where, c is the velocity of the light in vaccum (where air does not exists). v is the velocity of light in medium. And n is the index of refraction or refractive index, since it's variable could be shown by n or n'. Besides, measuring the refractive index formula is, $n = \frac{sin i }{sin r}$, where, i is angle of incident. r is the angle of refraction and the n is refractive index.

Answer 2

absolute refractive index is defined as a ratio of the speed of light in the vacuum and in selected medium  

relative refractive index is defined as a ratio of speed of light in two different media

When in relative refrective index ,second medium is vacuum then both will be same