Talk:Magnetic dipole

Back to being an article

This page was changed from a redirect to an article following a discussion of a need for such a page at Wikipedia talk:WikiProject Physics#Treatments of the magnetic dipole field. RockMagnetist (talk) 01:24, 8 August 2011 (UTC)

Review as requested by RockMagnetist

RockMagnetist asked what I felt about this article on talk:magnetic field. This is my reponse. First, I like the overall approach for this article, despite the fact that in physics at least it is a little non-standard. It does assume a certain level of sophistication (Calc III and junior level E&M) on the part of the reader. I don't see a reason for a non-technical reader to have much interest in this article, though. I also like the way it comes straight to the point and is parsimonious with words. This article does not need too much work. My main criticism is that I think it jumps too quickly to the magnetic potentials without sufficiently, IMO, motivating how the magnetic moment relates to the magnetic potentials. For that reason, I recommend adding two more sections: a short qualitative description section of the two models of the magnetic moment and a section on the potentials perhaps showing the Poisson's equations that lead to the solutions of A and φ used in the first section of the current article. Good work. TStein (talk) 20:10, 25 November 2011 (UTC)

Thanks for the suggestions, TStein. RockMagnetist (talk) 01:50, 26 November 2011 (UTC)

It's like, if you can understand the lede then you don't need to be reading this. The rest of us are thinking - huh!? Richard Avery (talk) 14:22, 19 January 2013 (UTC)

I have copied much of the technical stuff of this article over to magnetic moment and I am thinking about changing the focus of this article to be a qualitative description of the magnetic dipole with appropriate links to the more technical details on other articles. Does anyone have any thoughts on that? TStein (talk) 21:48, 31 May 2018 (UTC)

Force equation between two dipoles is wrong

It should go like this:

${\vec {F}}_{ab}={\frac {3\mu _{0}}{4\pi |r|^{4}}}[({\hat {r}}\times {\vec {m}}_{a})\times {\vec {m}}_{b}+({\hat {r}}\times {\vec {m}}_{b})\times {\vec {m}}_{a}-2{\hat {r}}({\vec {m}}_{a}\cdot {\vec {m}}_{b})+5{\hat {r}}(({\hat {r}}\times {\vec {m}}_{a})\cdot ({\hat {r}}\times {\vec {m}}_{b}))]$

where ${\hat {r}}$ is unit vector pointing from magnetic moment $m_{a}$ to $m_{b}$, and $|r|$ is the distance between those two magnetic dipole moments. — Preceding unsigned comment added by Ze-aksent (talk • contribs) 23:08, 19 November 2012 (UTC)

Do you have a citation for that? The existing equation does. RockMagnetist (talk) 23:24, 19 November 2012 (UTC)

Here: http://downloads.hindawi.com/archive/1998/079537.pdf

These guys say they were the fist ones to derive it, in 1998. They used vector differential and path integral derivation and arrived to the same equation. Ze-aksent (talk) 04:44, 23 November 2012 (UTC)

By the way, the existing citation links to document where the relevant page 140 is no available. — Preceding unsigned comment added by Ze-aksent (talk • contribs) 06:49, 23 November 2012 (UTC)

Both expressions are correct. You can get from this expression to the one in the article using the triple product expansion. RockMagnetist (talk) 18:47, 23 November 2012 (UTC)

Can you show me? -- And do you have citation for that equation in the article? Current reference is missing the page where that equation supposedly came from. Do you have some actual reference?

Ze-aksent (talk) 04:54, 24 November 2012 (UTC)

We're discussing this in two places. Let's have one conversation at Talk:Magnetic moment. RockMagnetist (talk) 05:23, 24 November 2012 (UTC)

Ok, just please give me some actual reference to that equation in the article.

Ze-aksent (talk) 10:06, 24 November 2012 (UTC)

Bad URL (?)

The URL for "Permanent Magnet and Electromechanical Devices: Materials, Analysis, and Applications" is http://books.google.com/?id=irsdLnC5SrsC&dq=permanent+magnet+and+electromechanical+devices&printsec=frontcover&q=3.130.

The q= causes the Google book to search for 3.130, which seems to me wrong. — Preceding unsigned comment added by 2601:18F:800:C4A1:9D8A:58CB:33FA:F9CE (talk) 17:23, 30 July 2016 (UTC)

Thanks for pointing this out. Normally, we shouldn't include a url for a Google Books search result, but this might be an exception. The source is being used for a particular equation which is in fact equation 3.130 in that book, and since it's a snippet view it's hard to see how else the equation could be viewed. However, I think it would be less confusing if I moved this reference out of References and into the citation. RockMagnetist(talk) 18:07, 30 July 2016 (UTC)

Field formula is wrong

Both parts of the field should vary with radius as 1/r^3 (e.g., Jackson eq. 5.56) David s graff (talk) 20:17, 16 March 2017 (UTC)

I presume you're referring to the first term in the second equation. The symbol $\mathbf {r}$ refers to the full vector, not a unit vector, so the numerator is proportional to r^2. RockMagnetist(talk) 15:25, 17 March 2017 (UTC)

Removal of explicit statement of units

@Jordi Burguet Castell:. Your edit summary is not strictly correct. One cannot change the system of units in electromagnetic expressions at will. The form of the expressions is different in different systems of units. See Centimetre–gram–second system of units#Derivation of CGS units in electromagnetism. Having said that, I support your removals. When I was a student we were expected to be familiar with four systems of units (FPS, CGS, MKS, SI and several variants) and be able to convert between them. Nowadays, SI can be assumed unless stated otherwise. SpinningSpark 08:39, 6 October 2021 (UTC)

@Spinningspark:. I see, thanks for the clarification. It is a bit more subtle to explain, the way I understand it, since the formulae are different depending on the system of units. The fact would remain that, given a system of units (which imply a concrete form of the formulae), the actual units will depend on the units used for the different quantities. Or, in other words, you could say things like "in the SI system", but not "in Tesla". Right? --jbc (talk) 17:43, 13 October 2021 (UTC)

If you mean that, for instance, field strength may be measured in kV/m rather than the unprefixed unit, then yes, you are right. SpinningSpark 19:03, 13 October 2021 (UTC)