On the energy of a magnetostatic field

Abstract

Certain facts cast some doubt upon the ‘plus’ sign of the term for the energy flux of a magnetostatic field in the Poynting formula. To cite an example, consider two equal point charges moving uniformly with equal velocities. Generally the electric repulsive forces act on the charges, being directed along the line connecting them. At the same time, components of the magnetic attracting forces act along the same line, and so the work required to bring the charges together is smaller than if magnetic interaction were absent. This fact motivates the hypothesis that the energy of a magnetostatic field is negative. A force action of electrostatic and magnetostatic fields localized in a uniformly moving ellipsoidal layer on a point charge moving synchronously outside the layer is discussed using the virtual work principle. It is shown that in order to avoid violation of the principle of the conservation of energy (as well as of the relativity principle) the energy of a magnetostatic field must be negative. In our proof we are dealing with the energy of ‘co-occurrence’ of two simplest objects of classical electrodynamics – the point charges q_T and q_C. The entire space around the charge q_C may be considered as subdivided into spherical (or ellipsoidal) layers; for each of these layers the theorem on negativity of the energy of a magnetostatic field is proved