The index of refraction, n, of a material medium describes how fast light travels through that medium in relation to the speed of light in vacuum. That is n = c / v, where c is the speed of light in vacuum (3.0 x 108 m/s) and v is the speed of light in the medium. With this definition, the refractive index of vacuum is nvac = 1. Since the speed of light is slower in a material medium, the index of refraction for any material is always a number greater than 1.
Although the speed of light changes as it goes from one medium to another, the frequency of the light remain unchanged. As a result, the wavelength of light therefore changes as it goes from one medium to another.
The speed of light in air at atmospheric pressure is 99.971 % the speed of light in vacuum. What is the difference of the index of refraction of air and the index of refraction of vacuum?
nair - nvac =