The velocity of light in a medium is 1.5 × 108 m/s. What is the refractive index of the medium with respect to air, if the velocity in air is 3 x 108 m/s?

Solution : Here, v₁ = 1.5 × 10⁸ m/s and v₂ = 3 x 10⁸ m/s.

We know that, the refractive index with respect to air is

₂η₁ = v₂ ÷ v₁ = (3 x 10⁸ ) ÷ (1.5 × 10⁸ ) = 2

Thus, the refractive index of the medium with respect to air is 2.