I know that in a vacuum,
Does this apply to any medium, so that
and its index of refraction is related to its dielectric constant and relative permeability by
I tried this for water, which has a dielectric constant of about $80$ and a relative permittivity of about $1$, but then the index of refraction is about $8.9$ when its actually $1.33$. Where did I go wrong in my assumptions/calculations?