Electromagnetic Momentum and Energy

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Discussion Overview

The discussion revolves around the concepts of electromagnetic momentum and energy, exploring their definitions, behaviors in various contexts, and mathematical representations. Participants share their understanding and seek clarification on these concepts, which are fundamental in physics and engineering.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses initial skepticism about the concepts of electromagnetic momentum and energy, indicating a preference for understanding through examples rather than derivations.
  • Another participant inquires if the discussion pertains to various forms of electromagnetic radiation, such as radio waves and photons.
  • A participant asserts that any electromagnetic field has an associated energy, providing a mathematical expression for energy density involving electric and magnetic fields.
  • Another participant clarifies that the provided equation relates to stored energy density and compares it to electrical engineering equations, also introducing the Poynting vector as a measure of electromagnetic energy flow.
  • One participant mentions that certain pages derive conservation laws for electromagnetic energy and momentum from Maxwell's equations.
  • A later reply expresses gratitude for the shared links, indicating they found the information helpful.

Areas of Agreement / Disagreement

The discussion includes various viewpoints and interpretations of electromagnetic momentum and energy, with no consensus reached on the best approach to understanding these concepts. Participants share differing perspectives on the mathematical representations and physical implications.

Contextual Notes

Some participants rely on specific mathematical expressions and comparisons to other fields, which may depend on particular assumptions or definitions that are not fully explored in the discussion.

quantoshake11
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I've been presented with these concepts, and the first time i saw them i thought they were just mathematical mambo-jumbo, but of course i didn't gave much importance to these thoughts. I've been constructing an idea of these after seeing how they behave in different circumstances, but really, i just seem to make a sense out of them from the examples and not from the 'derivation' they gave me. they're quite strange concepts, and i just wanted you guys to throw me some facts about them to chew in a bit and give a sense of them :)
 
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Are you talking about radio waves, visible light, x-rays, photons, etc?
 
well, as far as i know, any EM field will have an energy associated with it. the expression for it would be
(1/2)*[tex]\int E^2+B^2[/tex]
This would be valid for any EM field, including light. the integral is taken over a certain volume, and you can get the energy density as the limit.
 
The equation you are writing relates to the stored energy density in a volume. It is the physics version of such electrical engineering equations as (1/2) L I2 and (1/2) C V2. The electromagnetic energy flow is given by the Poynting vector P = integral[E x H] dA, which relates to the electromagnetic power flowing across an area element dA.
 
These pages derive electromagnetic energy and momentum conservation from Maxwell's equations.
 
thanks. those links really helped :)
 

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