Talk:Poynting's theorem

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Isn't the right side the negative of the total power done by the electric field? Not work... --Bmk 15:01, 25 July 2006 (UTC)

Oh, and isn't it actually power per unit volume? --Bmk 15:02, 25 July 2006 (UTC)

Yes. Fixed now. JRSpriggs 05:30, 26 July 2006 (UTC)

I think phasor poynting's theorem should also be mentioned in this page. -- (talk) 23:20, 1 January 2008 (UTC)Özgür


Hello, this statement is totally wrong : "Poynting's theorem takes into account the case when the electric and magnetic fields are coupled – static or stationary electric and magnetic fields are not coupled. In other words, Poynting theorem is valid only in electrodynamics." take a look at the feynman course. Wwe can define a poynting vector for a single particle with constant velocity, all the discussiàon bout electrodynamic momentum talks about that. — Preceding unsigned comment added by (talk) 09:34, 24 June 2011 (UTC)

Where is E × B ?[edit]

Near the bottom the article says "Instead of the flux vector E × B as above ...". Where does E × B appear above? (I was hoping to be able to refer to it.) Vaughan Pratt (talk) 02:41, 10 January 2014 (UTC)

Cumbersome derivation in "Derivation" section[edit]

The derivation in the section entitled "Derivation" could be done simply by differentiation. Going back and forth between the integral statements and the pointwise statements (several times!) is a red herring. It subjects the reader to a pedagogical rehash of the geometric justification for the divergence theorem, whether he wants it or not.

Inconsistencies throughout article[edit]

(1) The article defines the Poynting vector S to be "the energy flux vector", rather than giving a specific formula. That is fine. But the definition is not made "out loud", but only implicitly -- one is forced to infer it from the proof of Poynting's theorem. That is not so good.

(2) The main problem I have with this article: it goes back and forth several times between S = E x B and S = E x H, between J and J_f, and between a vacuum and a medium.

For example, early in the article we hear about "free" current, but then we switch to just E and B, then suddenly we have constitutive relations, but they are merely the constitutive relations of empty space. Then we proceed to derive (to prove) that S = E x H. Then we're told that we really did S = E x B (!!!). This does not match the S = E x H definition given under Poynting vector.

What is the correct setting for proving the theorem? Do I need to consult a medium, or decide in a vacuum?

(3) At the end we are told that we could have gotten S = E x H, S = D x B, or even S = D x H, and that the content of Poynting's theorem is different depending on what we got. In the words of the text:

It is possible to derive alternative versions of Poynting's theorem. Instead of the flux vector E × B as above, it is possible to follow the same style of derivation, but instead choose the Abraham form E × H, the Minkowski form D × B, or perhaps D × H.


The Poynting theorem we proved here was established independently of these conclusions. It made no commitment as to whether S = E x B or S = E x H. How can the theorem have different versions depending on the formula we later discover for S? Is Poynting's theorem the "continuity"-type statement

where S is defined to be the energy flux, or is it the conclusion S = E x B, where S is defined to be the energy flux? Or is it the formula that's obtained by substituting E x B for S in the boxed formula?

Are the hypotheses or definitions different, to get different theorems? In that case, what are these variable hypotheses?

Why don't we get S = E x H, like in the article Poynting vector? Or do we?

It seems that the definitions and background assumptions are constantly oscillating back and forth in this article. (talk) 00:44, 24 May 2015 (UTC)

Pretty devastating takedown, if I say so myself. Is there such a thing as a C-class article? (talk) 20:47, 15 October 2015 (UTC)
There is. I'm going to try to wade through the subject to figure out what the correct form of the equations should be. --Ipatrol (talk) 19:58, 18 October 2017 (UTC)