Mechanical forces of electromagnetic origin

Abstract

EXPERIMENTS have been reported which verified that at low frequencies a time-varying polarisation P in a dielectric, if taking place in a magnetic field H, results in a mechanical force of density Ṗ×μ0H. This force is not predicted by the Minkowski energy momentum tensor, but the Abraham form of that tensor gives a force density in an homogeneous isotropic body of magnitude [(ɛrμr−1)/c2]∂//∂t(E×H) usually called the ‘Abraham Force’. In a dielectric this can be written Ṗ×μ0H+P×μ0Ḣ. It is not surprising that Ṗ×μ0H should give a mechanical force, since Ṗ corresponds to a movement of electric charge associated with polarisation, but it is difficult to understand why P×μ0Ḣ should give a force.