Question

A student when discussing the properties of a medium (except vacuum) writes : 

Velocity of light in vacuum = velocity of light in medium. This formula is 

(a) dimensionally correct 

(b) dimensionally incorrect 

(c) numerically incorrect 

(d) Both (a) and (c)

Answer 1

Correct option: (d) Both (a) and (c)

Explanation:

The formula can be written as

velocity of light in vacuum / velocity of light in medium =1

This formula is dimensionally correct as both the sides are dimensionless. Numerically, this ratio is equal to refractive index which is > 1. Hence, the equation is numerically incorrect.