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I understand that, broadly speaking, Poynting's theorem is a statement of conservation of energy.

Energy density of a volume of current and charge decreases proportionally to work done on charges within the volume and by energy flux through the surface bounding the volume.

The energy flux term is the area integral of the Poynting vector.

My question is this: is this energy flux that is described by the Poynting vector a form of electromagnetic radiation? If not, how is energy radiating out of the charge and current distribution if not by work done on charges?

Sigma
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1 Answers1

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My question is this: is this energy flux that is described by the Poynting vector a form of electromagnetic radiation?

Poynting vector quantifies energy that is being lost from a region of space. Integral of this vector over its boundary gives total energy region loses per unit time. EM radiation is a different concept: when you are far from the sources, the EM field can be described as transverse wave. That is EM radiation - EM field far from its source.

Ján Lalinský
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  • Yes, because the total field is a near field "attached" to the charge (like a Coulomb field) plus a radiated field, which can be absent in case of a uniformly moving charge. – Vladimir Kalitvianski Feb 01 '15 at 19:39