A note on the formulation of the Maxwell equations for a macroscopic medium

摘要

In formulating the Maxwell equations for electrodynamics in the presence of a macroscopic continuous medium, it is common among standard textbooks to simply borrow expressions for the polarization charges and magnetization currents derived in electrostatics and magnetostatics, without much explicit justifications for using them in electrodynamics. Here we emphasize that these quantities must be introduced without resorting to results in statics, and must be derived directly from their definitions which remain valid in the general situation of electrodynamics.