Poynting's Theorem in Griffiths' Electrodynamics

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  • Thread starter Thread starter Zubair Ahmad
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Discussion Overview

The discussion revolves around Poynting's theorem as presented in Griffiths' Electrodynamics, specifically focusing on the nature of moving charges and their implications in the context of electric and magnetic fields. The scope includes theoretical considerations and conceptual clarifications regarding charge movement and current density.

Discussion Character

  • Conceptual clarification, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions which specific charges Griffiths refers to and the reasons for their movement.
  • Another participant asserts that currents arise from moving charges and that charges can accelerate due to forces from electric and magnetic fields produced by other charges.
  • A third participant reiterates the generality of the proof, suggesting that any charges can be considered as moving for various reasons.
  • A later reply points out that while the current density J is related to the motion of charges, Griffiths' use of Ampère-Maxwell law connects it to electric and magnetic fields from different sources.

Areas of Agreement / Disagreement

Participants express differing views on the specifics of charge movement and its implications, indicating that multiple competing interpretations exist without a clear consensus.

Contextual Notes

The discussion does not resolve the assumptions regarding the nature of the charges or the definitions of the electric and magnetic fields involved in the theorem.

Zubair Ahmad
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In Griffith's electrodynamics he writes about poynting's theorem.He considers some charge and current configuration. Then he says that these charges move.Which charges is he talking about and why would they move?
 
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What's your objection to moving charges? Currents are produced by moving charges. In general, a given charge can also accelerate due to the forces experienced by the electric and magnetic field produced by the other charges.
 
Zubair Ahmad said:
Which charges is he talking about and why would they move?
Any charges moving for any reason. It is a general proof.
 
Dale said:
Any charges moving for any reason. It is a general proof.
Ok the current density J which comes in proceeding steps is due to motion of these charges but when he uses ampere Maxwell law he relates it to same E and B which are due to some other source.
 

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