Definition :
“The ratio of the velocity of light in a vacuum to its velocity in any medium.”
The refractive index, also called the index of refraction, describes how fast light travels through the material.
Refractive indexes have no dimensions. The refractive index is the proportion between the speed of light in a vacuum (C) and the speed of light in a particular medium for a certain substance (V).
The refractive index for a medium is represented by n, then it is given by the following formula:
The direction of the light ray varies or it bends at the boundary separating the two mediums depending on the refractive index of the medium. The light ray bends toward the normal if it passes through a medium with a higher refractive index; otherwise, it bends away from the normal.