Question

Relation between refractive index and phase velocity

Answer 1

Thus by knowing the speed, or velocity, of light in that particular medium, we can find out its refractive index.

BTW, in this question I used speed and velocity differently, even though speed is a scalar quantity(magnitude only) while velocity is a vector quantity(magnitude and direction), because light travels in a straight line and so velocity of light in a medium = speed of light in that medium.