Monday, July 12, 2010

Does Uniformly Accelerating Charge Radiate?

One would think that the simple answer to this is yes. However, a lot have been said and discussed (not to mention, published) on this problem. What appears to be a standard problem and treatment in Jackson's "Classical Electrodynamics" turns out to have a lot more to it than first meets the eye.

The latest discussion on this was published just a few days ago.

D.R. Rowland, Eur. J. Phys. v.31, p.1037.

Abstract: A core topic in graduate courses in electrodynamics is the description of radiation from an accelerated charge and the associated radiation reaction. However, contemporary papers still express a diversity of views on the question of whether or not a uniformly accelerating charge radiates suggesting that a complete physical understanding of the energy content of the fields surrounding an accelerating charge is still missing. It is argued in this paper that the missing insight is the precise physical meaning of the somewhat mysterious 'Schott energy' which is shown to be simply the difference between the energy in the bound electromagnetic fields of the accelerating charge and the amount of energy in the bound fields of a uniformly moving charge which has the same instantaneous velocity. This difference arises because the bound fields of a charge cannot respond 'rigidly' when the state of motion of a charge is changed by an external force. During uniform acceleration, the rate of change of this difference is just the negative of the rate at which radiation energy is created, and hence the power needed to accelerate a charged particle uniformly is just that which is required to accelerate a neutral particle with the same rest mass even though the charge is radiating. The errors in other analyses are also identified.

Published 9 July 2010

Note that you can get free access to the online paper within the first 30 days of online publication.

Zz.

1 comment:

Will Orrick said...

The intuition from classical E&M is that a uniformly accelerating charge should radiate, but the intuition from everyday experience is that a charge at rest in a gravitational field should not. The question is, how does one reconcile these two intuitions with the equivalence principle?