Talk:Magnetic field

Magnetic pole model

Hi all, so I am going to chalk my sandbox up to a learning experience. I will try to see what I can do to improve the article over time, though. I added in the history section from my sandbox which had minimal changes outside of the record magnetic fields part, which I attempted to clean up some. I have added a citations needed section template to the magnetic pole model section. The section will be removed in a week's time if no reliable references are furnished supporting verifiability and the notability of the topic for this page. I do not think it belongs here, in either case (and I know I am not the only one). However, this will give those who may disagree a chance to fix the problem first. Otherwise, I will be renaming the Ampere loop model section to cut out all the talk of models and we can radically simplify those sections. The information about modern interest in magnetic poles can be kept, as it is referenced, but can be moved to another section. Comments are always welcome, thanks! Footlessmouse (talk) 19:42, 17 October 2020 (UTC)

I'm good with removing it and cutting out the talk of "models". That elevates them above what they really are - ways of calculating the magnetic field for various cases. In the case of the magnetic pole model, it is just a formal solution for zero electric and displacement current, and it's convenient to use the label "magnetic charge density" for a couple of terms inside the integral. Nobody thinks the charges actually exist. Anyway, the details of this solution are somewhat technical and are covered in Demagnetizing field. RockMagnetist(talk) 05:23, 20 October 2020 (UTC)

I agree with both. Models don't belong here. A sentence can be added somewhere saying where to find these models and what good they can do. Ponor (talk) 05:54, 20 October 2020 (UTC)

Efficacy of H and B in the continuity of magnetic fields

Hello. This is actually a continuation of the H versus B discussion. My position is evolving towards:

The $\mathbf {H}$ field should not be depreciated but it can be discussed after the $\mathbf {B}$ field.

I'd like to highlight a couple of bits of information. First, from Griffiths, who is somewhat disdainful toward the $\mathbf {H}$ field, "Many authors call $\mathbf {H}$ and not $\mathbf {B}$ the magnetic field." So, right there you have Griffiths, who is a reliable source, admitting that many authors call H and not B the magnetic field. He doesn't say that most authors prefer one or the other or that modern writers gravitate toward one or the other. Just that many authors say H and he thinks that is not a good idea. And then there is Jackson whose says unequivocally that $\mathbf {H}$ is called the magnetic field. (page 13 in the third edition).

Finally, I would like to direct your attention to the continuity equations of the magnetic field as given by Jackson an page 18.

$(\mathbf {B_{2}} -\mathbf {B_{1}} )\cdot \mathbf {n} =0$ where $\mathbf {n}$ is the vector normal to the interface surface. Roughly this means that the normal component of the $\mathbf {B}$ field is continuous across a boundary.

and

$\mathbf {n} \times (\mathbf {H_{2}} -\mathbf {H_{1}} )={\frac {4\pi }{c}}\mathbf {K}$ where $\mathbf {K}$ is surface current. This reduces to $\mathbf {n} \times (\mathbf {H_{2}} -\mathbf {H_{1}} )=0$ if there is no surface current. Roughly this means that the tangent component of the $\mathbf {H}$ field is continuous across a boundary. Even Griffiths writes it in this form (Eq. 7.62 on page 332 in the 3rd edition). Seems like there is something lost in writing this as $\mathbf {n} \times ({\frac {\mathbf {B_{2}} }{\mu _{2}}}-{\frac {\mathbf {B_{1}} }{\mu _{1}}})=0$

This shows up when you consider a solenoidal winding on a cylindrical core. The H field from the coils is roughly tangent to the walls of the cylinder so H is continuous across the cylindrical wall. H in the core is the same as H in the coils. B is continuous across the face of the cylinder. The ease of switching between H and B as needed to analyze the situation suggests to me that we need to keep both symbols. Constant314 (talk) 19:52, 24 November 2020 (UTC)

I haven't participated in this discussion for a while, but I was in at the beginning (as you were). Yes I definitely agree we have to keep H, as prominently as B. Not because it is called the "magnetic field", which is more an accident of history, but because it is used throughout electromagnetics and it is not going away. The graph universally used to give the magnetic characteristic of a material, the B-H curve, has H as one of the axes. It is really not a question of either-or, both fields are used in typical analyses of magnetic devices. One could be used, but it is usually more convenient to use both. I also respect RockMagnetist's opinion, as one of the most knowledgeable editors on this subject, and he says in this post physicists have not come to a consensus on whether one field is the most "fundamental". Even if they do, on the engineering level H is useful and is here to stay. I don't mind if it is presented in a separate section, if I remember we sort of decided to do it that way at one point in the previous discussion. --Chetvorno^TALK 20:34, 24 November 2020 (UTC)

I've all but given up on working this page. I had just started editing when I joined all those conversations and was in a little over my head. I don't believe we ever wanted to get rid of the H field, though, just relegate it to a section so the concept can be emphasized in a minimally confusing manner. It is obviously important and not going anywhere and must have a place on the page, it is more a matter of how the information is presented and if it can be done so in a way that isn't confusing to high school students. Footlessmouse (talk) 21:08, 24 November 2020 (UTC)

Footlessmouse I agree with everything you said. By the way, I've come across your work on a number of other pages. I respect your expertise, and all the time you've invested; you've made a great deal of improvement to the physics articles. Kudos! --Chetvorno^TALK 21:54, 24 November 2020 (UTC)

Examples of strong fields

The article seems blocked from editing but the example section ought to include examples of strong fields e.g:

ferrite (ceramic) magnets typically up to 0.35 T (remanent field inside magnet).

Neodymium magnets (and Alnico) up to 1.4 or possibly 1.5 T (remanent field inside magnet).

Electromagnets with iron core, typically up to 2 T.

Superconducting magnets typically used up to 20 T but higher theoretical limit.

Bitter electromagnet up to 37.5 T alone or 45 T in combination with superconducting magnet.

According to https://www.youtube.com/watch?v=-2QaTyDJDEI modern devices based on high-temperature superconductivity can reach 45 T. However a better reference would be needed.150.227.15.253 (talk) 10:47, 10 February 2021 (UTC) See also Superconducting_magnet#History for fields achived by superconducting magnets. 150.227.15.253 (talk) 11:24, 10 February 2021 (UTC)

Non-destructive pulsing can achieve 100 T (or at least that's the goal). https://nationalmaglab.org/education/magnet-academy/learn-the-basics/stories/magnets-from-mini-to-mighty

By explosive compression of magnetic fields transients of at least 200 T can be reached. in fact https://nationalmaglab.org/education/magnet-academy/learn-the-basics/stories/magnets-from-mini-to-mighty reports 1000 T.

The magnetic field on the surface of neutron stars is 10⁴-10¹¹ T.

There might be other astronomical record fields too.150.227.15.253 (talk) 11:21, 1 February 2021 (UTC)

The article is limited to editing by auto-confirmed or confirmed. Your additions look entirely reasonable, but would need reliable sources. Constant314 (talk) 15:18, 1 February 2021 (UTC)

I have given sources, what's wrong with them? Most are links to other Wiki articles. Shouldn't it be possible to refer to other Wiki articles assuming that they have done their job of finding reliable sources? Unfortunately Wiki has several different standards for including references and they are all rather awkward and it's difficult to find a good description of them. Some type of form for entering references would be nice. One could always require more sources but setting the standard requirements to high will just prevent people from making useful additions. A few of my sources are links to webpages of research groups that seem bona fide. People who find that the sources aren't good enough should be welcome to add more sources and to remove sources that become unnecessary by their additions. Errors and doubtful unsupported information need removal of course. Not having a sample list of magnetic field values (or only the Earth's magnetic field) is a larger shortcoming than not having done the job of a major review article.150.227.15.253 (talk) 14:24, 2 February 2021 (UTC)

WP itself is not usable as a source. See WP:CIRCULAR, specifically: Content from a Wikipedia article is not considered reliable unless it is backed up by citing reliable sources. Confirm that these sources support the content, then use them directly. I.e., porting sources over from another article is fine, but just linking to that article as a reference is not. --Elmidae (talk · contribs) 15:15, 2 February 2021 (UTC)

Semi-protected edit request on 2 August 2021

Please administrators, consider seriously eliminating the reference to pseudovectors in the heading of the article. It is unnecessarily misleading. Otherwise move it to the last element of the article as a marginal comment. Peqmeasy (talk) 16:09, 2 August 2021 (UTC)

I agree with removing pseudovectors from the lede. Let's see if anyone else also agrees. Constant314 (talk) 16:33, 2 August 2021 (UTC)

Agree, good idea. --Chetvorno^TALK 17:43, 2 August 2021 (UTC)

In general, the intro text should be rewritten. It's too specialized and confusing. Evgeny (talk) 06:36, 3 August 2021 (UTC)

• Done. Constant314 (talk) 06:51, 3 August 2021 (UTC)

Incorrect animation

The animation titled "The Amperian loop model" is incorrect on the right side. The poles should be moving left-right. The magnetic field should look like the graphic immediately above titled "The magnetic pole model". CEL3939 (talk) 15:06, 8 July 2023 (UTC)

Those aren't poles. That is where the current comes out of the picture and where the current goes back into the picture. Constant314 (talk) 00:15, 9 July 2023 (UTC)

OK, I see that now, thanks! I am used to seeing two poles of opposite sign moving closer together to produce a dipole source, and associated dipole field. CEL3939 (talk) 00:24, 9 July 2023 (UTC)