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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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