ABSTRACT
This chapter turns to the consideration of the distribution of energy and momentum of electromagnetic fields within material media, which is based on the discussion of the macroscopic form of Maxwell’s equations. A realistic electromagnetic wave is characterized by a finite spatial extent, so correspondingly contains a finite range of frequencies. This is relevant because the identification of the energy density according to involves a time integration, the building up of the field. But a field with a definite frequency has no such transient behavior; a range of frequencies is required.
