6.Refreactive Indext of Light From Medium 1 to Medium 2 and Vice Versa Relation

Refractive Index of Medium 1 to Medium 2 :
Refractive index for ray of light going from medium 1 to medium 2 is equal to the reciprocal of the refractive index for ray of light going from medium 2 to medium 1.

This can be proved in following way:

Suppose in first case ray of light is travelling from air to glass. Here air is taken as medium 1 and glass is taken as medium 2.
Let velocity of ray of light in air is v₁
and that of glass is v₂
we also know ₁μ₂ = v₁ / v₂

In this case we can write
Refractive Index (R.I.) of medium 2 = v₁ / v₂ – – – – – – – – – 1

Again suppose in second case light is travelling from medium 2 to medium 1 . Refractive Index (R.I.) of medium 1
= v₂ / v₁ – – – – – – – – – 2
I am again writing the equation 1
Refractive Index (R.I.) of medium 2 = v₁ / v₂

or Refractive Index (R.I.) of medium 2 = 1 / (v₂ / v₁)

= 1 / ₂μ ₁

∴ ₁μ₂ = 1 / ₂ μ₁

This can also be written as :
_airμ_glass = 1 / _glass μ _air