Refractive Index describes how light behaves as it passes through a medium, is the phase velocity or speed of light that is passing through a material compared the speed of light in a vacuum.
Refractive Index=Speed of light in vacuum
Phase velocity
The refractive index of air is about 1, and glass is around 1.52-1.62.
With the refractive index we can determine focal length and the angle at which light is refracted.
See also http://www.controlbooth.com/wiki/Refraction
And http://en.wikipedia.org/wiki/Refractive_index
Refractive Index=Speed of light in vacuum
Phase velocity
The refractive index of air is about 1, and glass is around 1.52-1.62.
With the refractive index we can determine focal length and the angle at which light is refracted.
See also http://www.controlbooth.com/wiki/Refraction
And http://en.wikipedia.org/wiki/Refractive_index