ABSOLUTE REFRACTIVE INDEX
The absolute refractive index of a medium is the ratio of speed of light in vacuum and the speed of light in the medium.
Absolute refractive index = Speed of light in vacuum or air
Speed of light in the medium
For example,
A.r.i of glass = speed of light in vacuum/speed of light in glass
3×10⁸/2×10⁸= 3/2=1.5
Its value is equal or more than 1. For vacuum or air, its value is 1. So its minimum value is 1.
RELATIVE REFRACTIVE INDEX
The relative refractive index of a medium (a) with respect to another medium (b) is the ratio of speed of light in medium (b) and the speed of light in medium (a).
Relative refractive index of (a) wrt (b)=Speed of light in medium (b)
Speed of light in medium (a)
For example,
r.r.i of glass with water=speed of light in water/speed of light in glass
=2.25×10⁸/2×10⁸=9/8=1.1
r.r.i of water wrt to glass= speed of light in glass/speed of light in water
=2×10⁸/2.25×10⁸= 8/9=0.88
Its value can be less than 1, more than 1 or equal to 1
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