On the covariant representation of integral equations of the electromagnetic field

TL;DR

This paper develops a covariant framework for integral equations in electromagnetism in curved spacetime, introduces a new physical quantity, and discusses limitations of the Kelvin-Stokes theorem in this context.

Contribution

It presents covariant formulas for electromagnetic fluxes and circulation, introduces the integral scalar potential, and analyzes the applicability of the Kelvin-Stokes theorem in curved spacetime.

Findings

Covariant formulas for electric and magnetic fluxes are derived.

A new physical quantity, the integral scalar potential, is introduced.

A new effect predicts magnetic field circulation without current or changing electric field.

Abstract

Gauss integral theorems for electric and magnetic fields, Faradays law of electromagnetic induction, magnetic field circulation theorem, theorems on the flux and circulation of vector potential, which are valid in curved spacetime, are presented in a covariant form. Covariant formulas for magnetic and electric fluxes, for electromotive force and circulation of the vector potential are provided. In particular, the electromotive force is expressed by a line integral over a closed curve, while in the integral, in addition to the vortex electric field strength, a determinant of the metric tensor also appears. Similarly, the magnetic flux is expressed by a surface integral from the product of magnetic field induction by the determinant of the metric tensor. A new physical quantity is introduced - the integral scalar potential, the rate of change of which over time determines the flux of vector potential through a closed surface. It is shown that the commonly used four-dimensional Kelvin-Stokes theorem does not allow one to deduce fully the integral laws of the electromagnetic field and in the covariant notation requires the addition of determinant of the metric tensor, besides the validity of the Kelvin-Stokes theorem is limited to the cases when determinant of metric tensor and the contour area are independent from time. This disadvantage is not present in the approach that uses the divergence theorem and equation for the dual electromagnetic field tensor. A new effect is predicted, according to which the circulation of magnetic field can appear even in the absence of electric current and with a constant electric field through the contour, if the area of this contour would change. By analogy with electromagnetic induction, for the magnetic field circulation to appear it is important that electric field flux that passes through the area of the contour would change over time.