Radiative losses and radiation reaction derived from the kinetic power of the electric inertial mass of a charge

Ashok K. Singal

Physical Research Laboratory, Ahmedabad

It is shown that formulas for radiative losses and radiation reaction from a charge can be derived from the kinetic power of its electric inertial mass. The derivation assumes a non-relativistic but otherwise an arbitrary motion of the charge. We exploit the fact that as the charge velocity changes because of a constant acceleration, there are accompanying modifications in its electromagnetic fields which can remain concurrent with the charge motion because the velocity as well as acceleration information enters into the field expression. However, if the acceleration of the charge is varying, information about that being not present in the field expressions, the electromagnetic fields get ``out of step'' with the actual charge motion. Accordingly we arrive at a radiation reaction formula for an arbitrarily moving charge, obtained hitherto in literature from the self-force, derived in a rather cumbersome way from the detailed mutual interaction between various constituents of a small charged sphere. This way we demonstrate that an irretrievable power loss from a charge occurs only when there is a change in its acceleration and the derived instantaneous power loss is directly proportional to the scalar product of the velocity and the rate of change of the acceleration of the charge.