Talk:Magnetic moment

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[edit] Cleanup required

I've marked this article for cleanup, due to its confusing and sometime incorrect explanations (see "Current, not poles" below). For a much better discussion of magnetic dipoles and magnetism, see magnetism.


ALSO The magnetic moment discussion here makes no mention to the magnetic moment in chemistry, only in physics. Can this hopefully be updated to include this information?

[edit] Current, not poles

The explanation of a magnetic dipole moment as being created by two poles separated by some distance is incorrect. This is true for electric dipole moments, but magnetic dipole moments are created by current loops, or by the aggregate effect of many intrinsic dipole moments, such as by many electrons whose spins are aligned, as in a bar magnet.

Magnetic monopoles, such as those implied in the discussion here, have never been detected, although there remains some possibility that they do exist. Even if they do, however, it is extremely unlikely that they are responsible for magnetism in the everyday sense.

[edit] Definition of Spin

I hate to be a pedant, but the table in the article says that spin is dimensionless. Spin is an intrinsic angular momentum and as such most definitely does have units. Its units are Js, the same as Planck's constant. Unfortunately, Planck's constant gets dropped from all the literature and text books either for brevity or when working in some natural units system, where c = h = 1. Earlier on in the article it does mention that electronic spin is a half times Planck's constant, but the table says it is dimensionless, which is likely to cause confusion (aside from the factual inaccuracy). --Lateralis (talk) 20:34, 1 May 2008 (UTC)

[edit] Molecular Dipoles

The page mentions the dipoles of electrons and nuclei, but molecules themselves have a dipole. It is of great importance in the field of chemical solvents and their respective miscibilities. This should be added.

[edit] unclear phrase

the phrase

  Any rotating charged object has magnetic moment from the earth to the electron.

is quite cryptic. Can anyone elaborate or rephrase? ~~

Better rephrasing would be: "Any rotating charged object (from as large as the earth to as small as electron) has magnetic moment"

This is also untrue. A uncharged rotating object will have no magnetic dipole moment.

I'm not sure what people are saying here. The earth has zero net electric charge, yet it does have a magnetic dipole moment (due to currents in the core, most likely). The electron is charged, and it has a magnetic dipole moment, but is it rotating? Hard to say; it has "spin", but that's an internal quantum number, and it's a point particle. The neutron is uncharged, but it does have a magnetic dipole moment. HEL 18:47, 5 November 2006 (UTC)

[edit] Vectors vs scalars

Am I right that in the equation mew = I A the current I is a scaler? If it is, that should be noted.

Corrected LeadSongDog 21:23, 17 May 2007 (UTC)

...In which case, in keeping with the notation employed (the arrow over μ to denote a vector) the vector surface area, defined as "a" in the article, should also be given an arrow. It may also be useful to say that the "vector surface area" means a "surface area with a unit vector normal to the plane". Moreover, tying in with the comment further down the page, it is probably a good idea to change "a" to something else, such as "s", so there is no ambiguity with the magnetic vector potential. --Lateralis (talk) 20:34, 1 May 2008 (UTC)

[edit] Start simple, then work up

While a novice reader will easily understand the definition in terms of a permanent magnet, the "magnetic moment in a magnetic field" will throw them very early in the article. It is good to keep the explanations/usages of the term itemized and summarized at the top of the article, but phrases should be added to distinguish them as different definitions (not in meaning, but in explanatory mechanism.) The separate paragraphs don't quite achieve this on their own.

Moreover, this lumping of a simple bar magnet in with a more complex relationship between magnet and another body/field continues in the "Explanation" section. It might be best to explain the stand-alone bar magnet longhand, e.g. give a few examples of a short powerful magnet and a big weak one. This may sound braindead, but it will help build confidence in the reader and encourage them to try to understand the next section, which would hopefully also be made more explicit. (71.233.165.69 01:49, 10 June 2006 (UTC))


[edit] A is a bad vector name

A is commonly used as the magnetic vector potential, and "a" as the surface normal vector.

[edit] Magnetic quadrupole moment and higher?

This page seems to equate "magnetic moment" with "magnetic dipole moment". This is wrong since there are magnetic quadrupole, octupole, ... moments as well. Either the page should be renamed "Magnetic dipole moment", or it should be changed to state "the most commonly encountered type of magnetic moment is the magnetic dipole moment" and then also mention the quadrupole, etc. HEL 18:50, 5 November 2006 (UTC)

[edit] Changes made

I'm a Physics-Major and currently enrolled in a course on Electricity and Magnetism, I am in the process of editing some of this page. I have changed the definition of the magnetic dipole at the top of the page to its correct definition.

[edit] phrase

This: (Curl your fingers in the direction of the current, your thumb will point in the direction a). sounds funky. Am I wrong in saying that you cannot curl your fingers in the direction of current (in a wire)? How do you curl fingers around the direction of a straight-moving thing? You curl your fingers around a conductor/wire in the direction of the magnetic lines of flux and then your thumb should be pointing in the direction of the current... or at least, that's what I was taught (and the old-timers with their "conventional current" will use a "left-hand rule"). However, I could have this all wrong/misunderstanding the author's meaning. Gaviidae 15:46, 2 March 2007 (UTC)

Partly right, in the example then the current is in a wire loop so it is a circular current and it is possible to curl your fingers along the current but the original author mixed up the right-hand rule and the right hand grip rule, I have fixed that.

Better to delete the funky elaboration, which is redundant at best. There's no need to explain the right hand grip rule here. Will snip it. LeadSongDog 20:19, 17 May 2007 (UTC)

[edit] proposed merge

No. Each article has a link to the other. I think a merge would not be in order.--Loodog 17:33, 25 April 2007 (UTC)

No. I dont think merging the two articles makes sense. —Preceding unsigned comment added by 130.89.95.129 (talk) 13:09, 8 October 2007 (UTC)

I agree, these pages shouldn't be merged. Magnetic moment is an abstract notion, and requires a definition, as well as explanations how to use it in calculations. The electron's moment is a natural phenomenon, and as such requires mention of its discovery, history, etc. —Preceding unsigned comment added by Xenonice (talk • contribs) 23:18, 7 November 2007 (UTC)

[edit] Template:Electromagnetism vs Template:Electromagnetism2

I have thought for a while that the electromagnetism template is too long. I feel it gives a better overview of the subject if all of the main topics can be seen together. I created a new template and gave an explanation on the old (i.e. current) template talk page, however I don't think many people are watching that page.

I have modified this article to demonstrate the new template and I would appreciate people's thoughts on it: constructive criticism, arguments for or against the change, suggestions for different layouts, etc.

To see an example of a similar template style, check out Template:Thermodynamic_equations. This example expands the sublist associated with the main topic article currently being viewed, then has a separate template for each main topic once you are viewing articles within that topic. My personal preference (at least for electromagnetism) would be to remain with just one template and expand the main topic sublist for all articles associated with that topic.--DJIndica 16:48, 6 November 2007 (UTC)