# Difference between Absoluteand Relative Refractive Index.

Dear Student
When light is going from vacuum to another medium, then the value of refractive index is called the absolute refractive index. When light is going from one medium (other than vacuum or air) to another medium, then the value of refractive index is called relative refractive index.

The absolute refractive index is defined as a ratio of the speed of light in vacuum and in selected medium. ... Relative refractive index is defined as a ratio of speeds of light in two different media.

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