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Starting with the most general form of Maxwell's macroscopic equations inwhich the free charge and free current densities, rho_free and J_free, as wellas the densities of polarization and magnetization, P and M, are arbitraryfunctions of space and time, we compare and contrast two versions of thePoynting vector, namely, S=ExB/mu_0 and S=ExH. Here E is the electric field, Hthe magnetic field, B the magnetic induction, and mu_0 the permeability of freespace. We argue that the identification of one or the other of these Poyntingvectors with the rate of flow of electromagnetic energy is intimately tied tothe nature of magnetic dipoles and the way in which these dipoles exchangeenergy with the electromagnetic field. In addition, the manifest nature of bothelectric and magnetic dipoles in their interactions with the electromagneticfield has consequences for the Lorentz law of force. If the conventionalidentification of magnetic dipoles with Amperian current loops is extendedbeyond Maxwell's macroscopic equations to the domain where energy, force,torque, momentum, and angular momentum are active participants, it will beshown that "hidden energy" and "hidden momentum" become inescapableconsequences of such identification with Amperian current loops. Hidden energyand hidden momentum can be avoided, however, if we adopt S=ExH as the truePoynting vector, and also accept a generalized version of the Lorentz forcelaw. We conclude that the identification of magnetic dipoles with Amperiancurrent loops, while certainly acceptable within the confines of Maxwell'smacroscopic equations, is inadequate and leads to complications whenconsidering energy, force, torque, momentum, and angular momentum inelectromagnetic systems that involve the interaction of fields and matter.

Nature of Electric and Magnetic Dipoles Gleaned from the Poynting Theorem and the Lorentz Force Law of Classical Electrodynamics