Question

what about relative refractive index​

Answer 1

Define relative refractive index. When we measure speed of light in two different media, relative refractive index of medium 2 with respect to medium 1 is defined as the ratio of speed of light in medium 1 to speed of light in medium 2.

Answer 2

When we measure speed of light in two different media, relative refractive index of medium 2 with respect to medium 1 is defined as the ratio of speed of light in medium 1 to speed of light in medium 2.