Reply to comment on `Poynting flux in the neighbourhood of a point charge in arbitrary motion and the radiative power losses'

TL;DR

This paper clarifies the interpretation of Poynting flux and radiative losses for an accelerating charge, addressing previous doubts and explaining the nature of the Schott term in electromagnetic theory.

Contribution

It provides a detailed reply to critiques of earlier work, clarifying the distinction between radiative energy flux and mechanical energy losses, and elucidates the nature of the Schott term.

Findings

Poynting flux is always positive at the retarded position.

Poynting flux can be negative at the present position of the charge.

The Schott term is the difference in energy rate change between retarded and present times.

Abstract

Doubts have been expressed in a comment (Eur. J. Phys., 39, 018001, 2018), about the tenability of the formulation for radiative losses in our recent published work (Eur. J. Phys., 37, 045210, 2016). We provide our reply to the comment. In particular, it is pointed out that one need to clearly distinguish between the rate of the energy-momentum being carried by the electromagnetic radiation to far-off space, and that of the mechanical energy-momentum losses being incurred by the radiating charge. It is also demonstrated that while the Poynting flux is always positive through a spherical surface centred on the retarded position of the charge, it could surprisingly be negative through a surface centred on the "present" position of the charge. It is further shown that the mysterious Schott term, hitherto thought in literature to arise from some acceleration-dependent energy in fields, is actually nothing but the difference in rate of change of energy in self-fields of the charge between the retarded and present times.