Light in Matter
In order to describe light waves in a material medium (i.e., not in a vacuum), some more vectors are required. Besides the electric and magnetic fields E and B and the current density J already introduced, the magnetic vector H and the electric displacement vector D are used to describe the electromagnetic wave in matter. In stable isotropic materials, the five vectors (E, B, D, H, J), together with the electric permittivity ε and the magnetic permeability μ already mentioned, plus the conductivity σ, are the material coefficients that manifest the effect of matter on the electromagnetic wave. In their simplest forms, the relations are
If the coefficients σ, ε, and μ are taken just as scalars, these purely multiplicative relations are at best an approximation of the complicated interaction of matter with electromagnetic waves, assuming as they do a directional isotropy of the material. An electromagnetic wave passing through a gaseous, solid, or liquid material of course will be affected differently, and further different gases, solids, and liquids will also have different effects on the wave depending on their gross structure and their molecular structure, and in ...