The flow of electromagnetic energy in the decay of an electric dipole
作者:
Hans Gregory Schantz,
期刊:
American Journal of Physics
(AIP Available online 1995)
卷期:
Volume 63,
issue 6
页码: 513-520
ISSN:0002-9505
年代: 1995
DOI:10.1119/1.17862
出版商: American Association of Physics Teachers
关键词: ELECTRIC DIPOLES;ELECTROMAGNETIC FIELDS;RADIATION FLUX;POYNTING THEOREM;MAXWELL EQUATIONS;BIOT−SAVART LAW;COULOMB FIELD
数据来源: AIP
摘要:
In a typical dipole decay, the induction magnetic field and the radiation magnetic field are in opposing directions. The former is dominant close to the decay, and the latter is dominant far away. Thus, there exists a surface on which these two components cancel each other, so that the magnetic field reverses direction. Because the magnetic field changes direction, so also will the Poynting vector field, provided the electric field is reasonably well behaved. This defines a ‘‘causal surface,’’ within which electromagnetic energy will collapse, and outside which the electromagnetic energy will radiate away. I present a simple example, the decay of a point electric dipole, to argue that the radiated energy comes, not necessarily from the accelerating charges themselves, but from the energy stored in the far field.
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