# Confusion on the indice of refraction: is it dependent on the frequency or not? [duplicate]

I saw in my course than when light hit a medium, it makes some dipole oscillating with the same frequency as the one of the light $$\omega$$. By a classical mechanics reasoning, one can show that the indice $$n=\frac{\epsilon}{\epsilon_0}$$ depends on the frequency, $$n=n(\omega)$$ A wave is scattered by the medium, and the way it is scattered depends on its wave length. What I don't understand is why do we talk about refraction indices of some medium $$n$$, since it depends on the nature of the incident wave ? Why for example, do we talk about the indice of refraction of water, or glass ? This is not clear for me. Any help would be appreciated.

• Does this answer your question? Intuitive explanation for why blue light is refracted more than red light? – Semoi Jul 12 at 14:57
• The index does vary with frequency but somewhat slowly over the range of frequencies covering visible light, so one can often take an average value without too much error. – ZeroTheHero Jul 12 at 15:05
• Could the downvoter please explain the reason of the downvote ? – Dicordi Jul 12 at 16:00
• @ZeroTheHero thank you this answers my question ! – Dicordi Jul 12 at 16:01