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 × 10) = 2
Thus, the refractive index of the medium with respect to air is 2.