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Refractive Index

(i) Refractive index of a medium is that characteristic which decides speed of light in it.

(ii) It is a scalar, unit less and dimensionless quantity.

(iii) Absolute refractive index :

When light travels from vacuum to any transparent medium then refractive index of medium w.r.t. vacuum is called it's absolute refractive index i.e. vacuumµmedium = c/v

Absolute refractive indices for glass, water and diamond are respectively µg = 3/2 = 1.5, µw = 4/3 = 1.33 and µD = 12/5 = 2.4

(iv) Relative refractive index :

When light travels from medium (1) to medium (2) then refractive index of medium (2) w.r.t. medium (1) is called it's relative refractive index i.e. 1µ2 = µ2/µ1 = v1/v2 (where v1 and v2 are the speed of light in medium 1 and 2 respectively).

(v) When we say refractive index we mean absolute refractive index.

(vi) The minimum value of absolute refractive index is 1. For air it is very near to 1. ( 1.003)