Upon travelling from a rarer medium to denser the light rays tend to bend towards the normal and if it travels from denser to rarer then it bends away from the normal at the point of incidence. The relative refractive index is the relative change in speed or velocity of light upon travelling from one given medium to another.
The absolute refractive index has one material medium and one vacuum in which the speed of light is 3 × 10 8 m/s. The type of refractive index depends upon the two mediums in which the light is travelling. The ratio of the velocities or speed of light in different media gives the refractive index. Whenever the light that tends to travel obliquely from one medium to another changes its direction while travelling from another, the extent of change in the direction of light rays is what we say and calculate as refractive index. The refractive index gives an idea about the speed of light while travelling in a different medium.
The index of refraction or in other words refractive index enables us to know how fast light travels through the material medium. Refractive Index first of all is a dimensionless quantity.
