Talk:Magnetic field

Magnetic field is neither a region nor a force

I disagree very strongly with the last edit and I don't know how to fix it. I have two problems with it. First, magnetic field is not a region nor is magnetic field limited to a region. Magnetic fields literally extend for as far as the eye (or telescope) can see. Second, and just as important the association of magnetic field with the word force is extremely misleading. The Lorentz force only applies to moving charges and forces on magnetic materials only occur for a non-uniform magnetic fields. Further, the integral of Bdl does not equal work done, etc. I realize that respected dictionaries use these terms, but it doesn't make it any less awful. TStein (talk) 21:02, 29 April 2018 (UTC)

Thanks to Chetvorno for interesting input/debate in previous discussion section, including nice illustrations of TStein's point that others can also make less-than-ideal definitions. Here is some more unpolished, raw material that might offer or inspire a way out of the gridlock -- at least in relation to the "region" question -- by simply avoiding to mention it. (when I used it, I was considering that a region can also be infinite...) This proposal does not address the "influence" vs. "force" debate. For now I have used "influence" (because something had to be used), but no prejudice is intended. (I also changed "electrical currents" to "moving electric charge" and added "permanently" to "magnetized materials" — for the sake of nontechnical readers). (I anticipate objections to "always observed" -- but will wait with explanations.) Sdc870 (talk) 10:03, 2 May 2018 (UTC)

Magnetic field is the physical phenomenon of the magnetic influence always observed with a moving electric charge and permanently magnetized materials. The strength and direction of the influence for each location in space, relative to the charge or magnetized material, is described mathematically as a vector field.  Sdc870

So, TStein, no objections? And if I introduced this text, you would not undo it? Sdc870 (talk) 22:32, 19 May 2018 (UTC)

Sorry, Sdc870, but I object. That is really awkward wording. Anyway, what is the problem with the current wording? RockMagnetist(talk) 05:19, 20 May 2018 (UTC)

"The first sentence should tell the nonspecialist reader what, or who, the subject is." MOS:FIRST

Much of previous discussion here elaborates various problems with first sentence (e.g., "vector field").

RockMagnetist What do you find awkward? Sdc870 (talk) 11:32, 10 October 2018 (UTC)

Sdc870, sorry, I also feel your version is not as good as the current wording, it just uses more words without adding information. The phrase "the physical phenomenon of the magnetic influence" is confusing. The definition of "vector field" currently in the first paragraph is more succinct and clear than yours. --Chetvorno^TALK 19:43, 10 October 2018 (UTC)

I see now the awkwardness in my proposal. But let me ask for a clarification: Is magnetic field supposed to refer to "vector field" (a mathematical construct) or "magnetic influence" (a physical phenomenon)? As I read the current first sentence, it refers to a mathematical construct (but not to a physical phenomenon). Is that the intention? Thanks. Sdc870 (talk) 20:31, 10 October 2018 (UTC)

As far as I can see, the whole first paragraph, when read in its entirety, addresses the issues that concern you. Attic Salt (talk) 21:59, 10 October 2018 (UTC)

I agree that the article as it stands is better than the proposal. I understand the discomfort with vector field in the first sentence, but I think it's useful to have those words there. Ccrrccrr (talk) 23:23, 10 October 2018 (UTC)

Magnetic pole model confuses

I believe that the section on the Gilbert magnetic pole model is not helpful as it stands. It may be of historical interest, but some of the statements in it are just plain wrong. No distribution of hypothetical magnetic "charges" can reproduce the field around a current carrying wire or solenoid, and it is not true that the H and B fields are antiparallel within a magnetic material. Even in the case of the external field around a magnetic dipole magnet, I believe the magnetic pole model only gives a qualitative approximation of the field. The model itself is inconsistent with the Maxwell equation stating that the divergence of the magnetic field is always zero. It isn't sufficient to acknowledge that magnetic monopoles have never been found, and say that the magnetic pole model of fields is merely "conceptual". It cannot give accurate quantitative results, and the misstatement about B vs. H within a magnetic material has caused a good deal of confusion about the subject. 73.93.173.170 (talk) 22:56, 24 June 2018 (UTC)

It's of more than historical interest because everyone who models magnetic domains in ferromagnets uses poles (but they don't call it the Gilbert model). You're right about there being a lot of inaccuracies, not to mention a lack of sources. I'll try to find time to rewrite it. RockMagnetist(talk) 00:20, 26 June 2018 (UTC)

I have been digging into this a bit more, and as far as I can tell the only author who refers to the magnetic pole model as the "Gilbert model" is David J. Griffiths (in his textbook on electromagnetics and other publications). It's not even clear which Gilbert he is referring to - is it T. J. Griffiths of the Landau–Lifshitz–Gilbert equation? So much for the historical interest. I think the reference to Gilbert should be dropped, here and in Force between magnets. But to clarify something I said above - the inaccuracies are in this article, not the model. Used correctly, the magnetic pole model gives the same results as the current loop model, but with less effort. I have plenty of sources to back this up, and I'll rewrite the section soon. RockMagnetist(talk) 18:03, 26 June 2018 (UTC)

I have to confirm RockMagnetist. An appropriate distribution of hypothetical magnetic "charges" can totally reproduce the precise magnetic field of a magnet, where there is no free current. This is because $\nabla \cdot \mathbf {H} =-\nabla \cdot \mathbf {M} =\rho _{m}$, so the H-field originates from the bound magnetic charge $\rho _{m}$. The charge $\rho _{m}$ is located where the magnetization changes ($\nabla \cdot \mathbf {M}$), that is at the end of the magnet. And if H can be calculated, then B can be as well via $\mathbf {B} =\mu _{0}(\mathbf {M} +\mathbf {H} )$. Now if there is free current, such as in a current carrying wire or a solenoid, the pole model may be helpful in some cases and not in others. The B-field of an ideal solenoid can be perfectly calculated with an uniform charge distribution on the solenoid's plane end facets, and later subtracting a constant M-field within the solenoid volume (see magnetic field of a cylinder magnet for an accurate example). For other configurations, such as a simple wire, no appropriate magnetic charge distribution might be found. However, I would also not call the pole model "Gilbert model", because that term doesn't seem to be widespread. --Geek3 (talk) 13:06, 18 January 2019 (UTC)

Should "magnetic influence" redirect to this article?

The phrase magnetic influence appears in the first sentence of this article (after which influence does not appear again in the article). A search in Wikipedia on "magnetic influence" redirects to "Magnetic pistol". Maybe "magnetic influence" should redirect to here? Sdc870 (talk) 23:53, 19 March 2019 (UTC)

The target should definitely not be magnetic pistol, a pretty obscure subject. I tried Googling "magnetic influence", and the top few hits were to some huckster called Dani Johnson. After which the next hit was Magnetism. So maybe that's the best choice. RockMagnetist(talk) 02:42, 20 March 2019 (UTC)

Maybe it needs to be marked as "magnetic influence (physics)" [though have not found it mentioned in textbooks] to differentiate it from this definition: (2009) magnetic influence. In: Manutchehr-Danai M. (eds) Dictionary of Gems and Gemology. Springer, Berlin. https://doi.org/10.1007/978-3-540-72816-0 :

"a believing that magnetite or magnetic power promotes the user to be straight forward, reality oriented, etc."

Also, right now, the Magnetism article does not address 'magnetic influence' directly, so it would be necessary to modify that article, if redirected there.

Sdc870 (talk) 09:51, 21 March 2019 (UTC)

I don't think such information would be appropriate on that page. A disambig page would be better. RockMagnetist(talk) 14:39, 21 March 2019 (UTC)

That is also what I was trying to suggest with "magnetic influence (physics)" (but I do not know how to make a disambiguation page). My other point was that right now the Magnetism page does not provide clear information about "magnetic influence (physics)". Did not mean to imply that the superstitious meaning should also be discussed. Sdc870 (talk) 15:00, 21 March 2019 (UTC)

"Magnetic pistol" isn't a terrible target choice for Magnetic influence, which is a common term for a class of naval weapons that are activated by magnetic fields. All 3 of the existing links to that redirect are correctly retargeted to magnetic pistol. There would be no pointto creating a parenthetically disambiguated redirect. VQuakr (talk) 15:53, 21 March 2019 (UTC)

Yes, the more I look into this the more I am leaning towards that point of view. In a search of uses of the term in Wikipedia, almost all refer to the military use. In physics articles, it's just a vague term that should probably be replaced by a more precise term. RockMagnetist(talk) 16:10, 21 March 2019 (UTC)

The expression has been used in non-military scientific texts for over 100 years: examples of the use of the phrase ‟magnetic influence” in physics journal articles, but more or less impossible to find in textbooks. Perhaps the word "influence" has to be removed or defined in the first sentence? Sdc870 (talk) 17:13, 15 April 2019 (UTC)

This seems to me to be an example of overdefining of terms ("redirect overkill"). Looking at the links given, I don't see that the term has a specific meaning, but as RockMagnetist says is a vague term whose meaning varies by context. Making it redirect to a specific article is implying a specificity of meaning that it doesn't have. I'd suggest deletion. --Chetvorno^TALK 12:11, 16 April 2019 (UTC)

I think a conversation about what to do with the redirect should be moved over to its talk page (or maybe Wikiproject Physics). As far as this article is concerned, we should begin by delinking it and then come up with a better wording. RockMagnetist(talk) 15:00, 16 April 2019 (UTC)

Correction: it isn't linked. I don't know why I thought it was. RockMagnetist(talk) 15:01, 16 April 2019 (UTC)

(copied this discussion to Talk:Magnetic influence#What should the target of this redirect be?)

Alternative names???

"Magnetic field" and "magnetizing field" are NOT alternatives for H. These are just the names "we" gave to these physical phenomena. H is a DESCRIPTION of these phenomena, but it's not the phenomena themselves! — Preceding unsigned comment added by Koitus~nlwiki (talk • contribs) 14:20, 4 June 2019 (UTC)

Are you proposing a change in wording? If so, where? RockMagnetist(talk) 16:52, 4 June 2019 (UTC)

Manipulation

Shaping of magnetic fields?? It seems there exists technology that allows to shape magnetic fields. Setenzatsu (talk) 22:34, 9 June 2019 (UTC)