Light is travelling in air, which has an index of refraction of 1. How fast does light travel in air?

Jun 11, 2017

Refractive index is defined as the following,

$n = \frac{c}{v}$ where $v$ is speed of light in the medium and $c$ is speed of light in vacuum.

Now if refractive index of air is $1$.

This gives, $v = c$

Thus light travels through air with the same speed it travels through vacuum. (This is only approximately true but, for most purposes this approximation is very precise.)

The speed of light in vacuum is $3 \cdot {10}^{8} m {s}^{-} 1$