Remark on some aspects of Maxwell’s equations

Abstract

Maxwell’s equations are written in a form containing onlyE andB and the electric and magnetic polarizations. It is shown that expressions somewhat deviating from the usual ones can be obtained for the energy density and thePoynting vector, if one separates carefully electromagnetic and non-electromagnetic sources of energy. The question of the ponderomotive force is discussed and it is shown that the state of a complicated physical system cannot be described by giving the value of its total energy and momentum and therefore no generally valid expression for the ponderomotive force can be given. All the same in any given case, when the mechanical properties of the system are taken into account, its behaviour can be understood.