Electromagnetism in Linear, Homogeneous and Isotropic Materials: The Analogy Between Electricity and Magnetism in the Susceptibility and Polarization.

Through the years, the asymmetry in the constitutive relations that define the electric and magnetic polarization, and , respectively, by the relevant vector field, and , has been imprinted, rather arbitrarily, in Maxwell's equations. Accordingly, in linear, homogeneous, and isotropic (LHI) materials, the electric and magnetic polarization are defined via = χε ('P-E, χ' formulation; 0 ≤ χ < ∞) and = χ ('M-H, χ' formulation; -1 ≤ χ < ∞), respectively. Recently, the constitutive relation of the polarization was revisited in LHI dielectrics by introducing an electric susceptibility, χ, which couples linearly the reverse polarization, P~ = -, with the electric displacement through P~ = χ ('P-D, χ' formulation; -1 ≤ χ ≤ 0). Here, the 'P-D, χ' formulation is generalized for the time-dependent case. It is documented that the susceptibility and polarization of LHI dielectric and magnetic materials can be described by the 'P-D, χ' and 'M-H, χ' formulation, respectively, on a common basis. To this end, the depolarizing effect is taken into account, which unavoidably emerges in realistic specimens of limited size, by introducing a series scheme to describe the evolution of polarization and calculate the susceptibility. The engagement of the depolarizing factor N (0 ≤ N≤ 1) with the accompanying convergence conditions dictates that the susceptibility of LHI materials, whether electric or magnetic, should range within [-1, 1]. The 'P-D, χ' and 'M-H, χ' formulations conform with this expectation, while the 'P-E, χ' does not. Remarkably, Maxwell's equations are unaltered by the 'P-D, χ' formulation. Thus, all time-dependent processes of electromagnetism described by the standard 'P-E, χ' approach, are reproduced equivalently, or even advantageously, by the alternative 'P-D, χ' formulation.