. What is Refractive Index.Explain
Light travels at different speeds in different optical media. Refractive index of a medium is a quantitative measure of how fast the ray travels in that medium. The refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in that medium
c: Speed of light in vacuum; v: Speed of light in the medium.
Higher the refractive index of a medium, slower light travels in that medium and vice versa.
From the definition it follows that refractive index of vacuum is unity. The refractive index of air is only slightly higher, and for most practical cases we take it as unity. Amongst two media of different refractive indices, the medium with higher refractive index is called optically denser medium or simply denser medium, and the medium with lower refractive index is called optically rarer medium or simply rarer medium.
Optical density should not be confused with mass density, which is mass per unit volume. It is possible that mass density of an optically denser medium may be less than that of an optically rarer medium. For example, turpentine and water. Mass density of turpentine is less than that of water but its refractive index is higher.
Often the refractive index of a medium is specified relative to another medium. Relative refractive index of medium 1 relative to medium 2 is defined as