In general it is equal to the square root of the product of the relative permeability and the relative permittivity. This ratio of speeds varies with the frequency of the radiation, a phenomenon known as dispersion. For a non- magnetic medium, it is equal to the square root of the dielectric constant. FTP, identify this material property appearing 
In general it is equal to the square root of the product of the relative permeability and the relative permittivity. This ratio of speeds varies with the frequency of the radiation, a phenomenon known as dispersion. For a non- magnetic medium, it is equal to the square root of the dielectric constant. FTP, identify this material property appearing in Snell's law, and often given the symbol n, which measures the ratio of the speed of refracted light in a medium.
In general it is equal to the square root of the product of the relative permeability and the relative permittivity.
{index of refraction} or {refractive index}