UPSC CDS 2 2020 GK Paper

In physics optics, the refractive index of a material is a unitless number that describes how faster the light travels through the material. It is defined as
n=

c

v

where,
c = speed of light in vacuum
v = phase velocity of light in the medium
So, If the speed of light in air is represented by c and the speed in a medium is v, then the refractive index of the medium can be calculated using the formula.