- #1
fisico30
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hello forum,
the famous Poynting theorem is an expression for the energy balance. Please, could anyone make sure I have the right understanding ?
The EM energy in a volume V with bounding surface S can change with time if:
1) energy leaves or enter that volume through S (net flux).
2) if the energy in the volume is used up by the free and induced currents and charges and then transformed into heat. Those currents and charges then behave as sinks.
3)If there are impressed sources (currents and charges) that generate new energy.
Regarding 2): the free and induced currents and charges could not only dissipate EM energy but also re-emit some of the absorbed energy once set into motion... so they would act as both sources and sinks.
In free space, there can only be free sources (if any) in the volume.
The dot product of E and J represents the lost power. Where is the charge density gone?
thanks
fisico30
the famous Poynting theorem is an expression for the energy balance. Please, could anyone make sure I have the right understanding ?
The EM energy in a volume V with bounding surface S can change with time if:
1) energy leaves or enter that volume through S (net flux).
2) if the energy in the volume is used up by the free and induced currents and charges and then transformed into heat. Those currents and charges then behave as sinks.
3)If there are impressed sources (currents and charges) that generate new energy.
Regarding 2): the free and induced currents and charges could not only dissipate EM energy but also re-emit some of the absorbed energy once set into motion... so they would act as both sources and sinks.
In free space, there can only be free sources (if any) in the volume.
The dot product of E and J represents the lost power. Where is the charge density gone?
thanks
fisico30