Angular momentum transfered by the field of a moving point charge

TL;DR

This paper derives general and far-field equations for the angular momentum flux of electromagnetic fields generated by a moving point charge, including explicit expressions and torque calculations related to the charge's motion.

Contribution

It provides new explicit formulas for angular momentum transfer and torque in electromagnetic fields of moving charges, extending previous understanding.

Findings

Explicit expression for angular momentum flux in the wave zone

Torque proportional to the curl of the Poynting vector in the far field

General equations for angular momentum transfer at arbitrary distances

Abstract

The flux of angular momentum of electromagnetic field of an arbitrarily moving point charge is investigated. General equations are obtained for the transfer of angular momentum at arbitrary distance from the charge, and corresponding equations in the far-field approximation. An explicit expression is obtained for the flux of angular momentum in the wave zone in terms of coordinates, velocity, and acceleration of the charge. The torque is calculated, that would act on an object if it absorbed all the radiation incident on it. It is shown that this torque is proportional to the curl of the stress tensor of the electromagnetic field; in the far field approximation the torque is proportional to the curl of the Poynting vector.