# Talk:Vacuum permeability

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## Sourcing commentary?

Is the commenting on the viability of a source really necessary, in particular, citing a source as a subject of "psuedoscience." Perhaps this sort of commentary can be relegated to discussion rather than in the article itself. —Preceding unsigned comment added by 70.89.72.122 (talk) 18:47, 21 October 2009 (UTC)

## μ or μ0?

I am confused by the statement, "The vacuum permeability μ = μrμ0 is equal to μ0." Taken out of context, the conclusion is that μr = 1. I suppose that the whole nomenclature section is confusing me. Ronstew (talk) 22:25, 19 November 2007 (UTC)

For the vacuum, μr = 1, as the relative magnetic permeability of substances is relative to the vacuum. /Pieter Kuiper (talk) 22:40, 19 November 2007 (UTC)

## naming

As per WP:NAME, the title of this page should be determined by common usage, and common usage overwhelmingly favors "vacuum permeability" and its variants ("permeability of vacuum" or "of free space") over "magnetic constant", despite the fact that the latter seems to be favored by standards organizations these days.

On a Google search of arXiv.org, there are 784 hits for the former names, and only 89 hits for the latter. On Google scholar, there are 14750 hits for the former, and 1590 hits for the latter. On Google overall, there are 143480 hits for the former terms and only 9350 hits for the latter.

Moreover, many of the hits for "magnetic constant", if you look closely, seem to be for something completely different. For example, in the first page of Google scholar hits, as far as I can tell none of the papers are using it for μ0. Several papers are using it for the relative permeability (in apparent analogy to "dielectric constant" for relative permittivity). There are also a number of papers that use it for an apparently completely unrelated astrophysical quantity (e.g. [1]).

In fact, there appear to be so many alternate usages of "magnetic constant" in widespread use that it looks like we need a disambiguation page for that term. (And its ambiguity is another reason not to use it as the title for this page.)

—Steven G. Johnson (talk) 01:37, 14 February 2008 (UTC)

A guideline in resolving naming conflicts is to check scientific nomenclature as used by professional bodies: Wikipedia:Naming conflict#Identification of common names using external references. Also, if one looks at the interwiki links, the sudden move by Stevenj goes against what most of the other wikipedias are using. /Pieter Kuiper (talk) 20:29, 14 February 2008 (UTC)
Read the whole page: that page lists ways to test which names are the most common, but the criterion is still which name is the most common—the guidelines are just giving examples of places to look. In this case, there is a clear disconnect in that the name that is most common with standards organizations is not even close to being the most common in professional usage by practicing scientists. (As for other languages, we're talking about terminology in English here, so it's not clear why that's relevant.) —Steven G. Johnson (talk) 23:02, 14 February 2008 (UTC)
Stevenj omits relevant passages on what the guidelines says. Wikipedia:Naming conflict#Proper nouns: "If the common name conflicts with the official name, use the common name except for conflicting scientific names". That should be clear, I think. /Pieter Kuiper (talk) 23:11, 14 February 2008 (UTC)
(Interesting, none of the other naming pages lists that exception IIRC.) In any case, that passage is not applicable because we are not dealing with an "official" name vs. an "unofficial" name. (This is not like "brontosaurus" vs. "apatosaurus" where one name has been explicitly deprecated.) As we've extensively discussed, the standards bodies haven't said that the other names are "wrong", or "incorrect", or "deprecated" (unlike, e.g. "dielectric constant"), or that there is only one "official" name for this constant. They have merely quietly, with no explicit statement of explanation or preference, chosen a particular synonym to use in their own documents (and many of the documents continue to list other synonyms as well, as we've discussed).
(And in this page, "magnetic constant" has another big strike against it in that it is ambiguous in current usage. Remember that the policy is to choose the least ambiguous common name.) —Steven G. Johnson (talk) 23:43, 14 February 2008 (UTC)

Magnetic constant is as official as scientific nomenclature can be. Stevenj's suddenly moving this article away from the official name was against the longstanding policy on scientific nomenclature stated in Wikipedia:Naming conflict#Proper nouns. So how to deal with Stevenj? Edit wars over article names are particularly disruptive. I think I will ask an administrator to move the article back to where it belongs. /Pieter Kuiper (talk) 10:00, 17 February 2008 (UTC)

There is zero evidence that "vacuum permeability" is "unofficial", as we have discussed ad nauseam; the mere fact that the standards bodies have implied a preferences (and continue to list "vacuum permeability" parenthetically) is not the same as explicitly deprecating the older term or making it "unofficial." (This is very different from things like names of species, where standards bodies clearly state that there is one and only one official scientific name of the species.) Hence, by longstanding Wikipedia policy, we should use the more common name, which is the older name by a large margin in any search of the literature, textbooks, etcetera. You are the one who has been fighting tooth and nail against WP policy (here and in vacuum permittivity). —Steven G. Johnson (talk) 18:23, 17 February 2008 (UTC)
Put another way, Pieter wants Wikipedia to take the position that the terminology used by most current practitioners in the field, and by most popular textbooks, is "unofficial" and obsolete. This is not the type of linguistic battle that Wikipedia fights, by policy.
(Although my biggest concern at this point in the two articles is not the naming, but the implication that the linear permittivity and permeability of vacuum can differ from ε0 and μ0, which is impossible by definition of the units, any more than the vacuum speed of light can differ from c. More pertinently for Wikipedia, it is original research because it directly contradicts all the authoritative published references. See Talk:Vacuum permittivity. —Steven G. Johnson (talk) 18:44, 17 February 2008 (UTC))

## Value of μ0

I have added a section on the historical reasons that μ0 has the value it does, in the hope that this will help readers understand what μ0 actually is and why it has the value it does. I have also made a couple of small changes elsewhere. The comment on the accuracy of realizing the ampere has been transferred to the article on the ampere. The comment about the vacuum state being a base state has been removed, because it appears to have little obvious relevance to the definition of μ0. I am of the firm opinion that this article should be about explaining that μ0 is a measurement-system constant with a value decided by convention, and should not confuse readers by trying to discuss properties of the vacuum. By all means discuss the latter in Wikipedia, but put the discussion in an article about the vacuum. (RGForbes (talk) 22:47, 25 March 2009 (UTC))

It is clear that some people (including myself) do not like the name "vacuum permeability", but that other people think that the article should use the name in most popular use – despite that fact that the official bodies appointed by our Governments to discuss issues like this have reached international agreement (actually for good reasons) to use the official name "magnetic constant" for μ0. Can I suggest that, as a compromise, this article is simply called μ0, with redirection pages from all the historical alternatives. I'll do this in due course if nobody objects. (RGForbes (talk) 22:47, 25 March 2009 (UTC))

Sounds fine to me. That will be a reminder to people of the change, and give them some time to get used to it. I do agree with the reasoning for the change, though I am not sure that there isn't a better choice for the name. Gah4 (talk) 22:05, 24 January 2011 (UTC)

Would it not just be easier to call it 'Permeability of free space'? I agree that 'Vacuum permeability' is vague, ambiguous and frankly lame, but μ0 isn't really much better. 178.107.82.56 (talk) 23:15, 22 April 2011 (UTC) Edited again due to typo :( 178.107.82.56 (talk) 23:16, 22 April 2011 (UTC)

I think it's a good idea to have this article and the analagous electric constant named similarly. Would you suggest changing both articles in a similar way? Larryisgood (talk) 08:02, 23 April 2011 (UTC)

## Thanks to the anonymous IP

Anonymous IP user 129.2.175.87 corrected either a computational error or pure vandalism by a previous anonymous IP editor. Thanks for doing that. Your talk page does not seem useful for this message so I left it here. Steve Quinn (formerly Ti-30X) (talk) 04:33, 18 February 2010 (UTC)

## Wholesale revert of Physchim62's changes

If one can do something like this, one should not edit here. /Pieter Kuiper (talk) 07:22, 1 April 2010 (UTC)

I was working from a reference: International Union of Pure and Applied Chemistry (1993). Quantities, Units and Symbols in Physical Chemistry, 2nd edition, Oxford: Blackwell Science. ISBN 0-632-03583-8. p. 117. Electronic version., which gives
${\mathbf {F}}={\frac {\mu _{0}I_{1}{\mathrm {d}}{\mathbf {\ell _{1}}}\times (I_{2}{\mathrm {d}}{\mathbf {\ell _{2}}}\times {\mathbf {r}})}{4\pi {\mathbf {r}}^{3}}}$
The third edition gives a slightly more rigourous version, with F replaced by d2F. Physchim62 (talk) 11:00, 1 April 2010 (UTC)
The mathematical level of your reference is above your capabilities, and you lack a conceptual understanding of fields. Better to use a highschool textbook. I really would advise you to stop editing physics articles when you do not even understand when the error has been pointed out to you. /Pieter Kuiper (talk) 11:45, 1 April 2010 (UTC)
So you're insisting that the force doesn't obey the inverse-square law (as well as being needlessly rude). Physchim62 (talk) 16:31, 1 April 2010 (UTC)
So you keep insisting that all textbooks got this wrong? Amusing. And the guy that accuses retired professors of being pseudoscientists thinks that I am rude... /Pieter Kuiper (talk) 16:38, 1 April 2010 (UTC)
Why don't you try keeping the tone down and actually providing an explanation of your position instead of lame insults? Physchim62 (talk) 17:15, 1 April 2010 (UTC)
You gave me a "last warning"? But you are too arrogant to look this up in a schoolbook? Something that has been known for almost 200 years? /Pieter Kuiper (talk) 17:24, 1 April 2010 (UTC)
Perhaps you would care to give me a reference? Or maybe you should read the article and ask yourself what is being defined by the equation and whether it actually fits with the text... Physchim62 (talk) 17:36, 1 April 2010 (UTC)
Can we keep it polite guys? Pieter's facts are correct, but its important to remember we should always present our positions with civility and understanding. FellGleaming (talk) 17:41, 1 April 2010 (UTC)
Understanding should be important when one edits what is used as an educational resource. Physchim embarked on a major edit of the article lacking any understanding of the basics, and he introduced the worst error in an important and well-known formula. /Pieter Kuiper (talk) 17:49, 1 April 2010 (UTC)
And you corrected one problem while creating another. Please just fix the edit and skip the insults. Gerardw (talk) 17:53, 1 April 2010 (UTC)

As it happens, the article says it is defining "force per unit length", not total force integrated of the length of the conductors, so the equation is wrong anyway. Physchim62 (talk) 18:01, 1 April 2010 (UTC)

Oh my, it really is Fools' Day. /Pieter Kuiper (talk) 18:02, 1 April 2010 (UTC)
If you had two infinitely long parallel wires (you can't really have those, as FellGleaming pointed out elsewhere, but you can talk about them as a limiting case of long wires), a finite distance apart, carrying finite currents, in vacuum, then the total force each exerted on the other would be infinite. For this reason, it makes more sense to talk about the force per unit length that each wire would exert on the other, which is finite. The formula for this in the article is correct as it is now, and I added a reference for it. Cardamon (talk) 20:15, 1 April 2010 (UTC)

## Rationalization factors

The factor for the rationalization of the electromagnetic units is 4π, not 2π. The figures of "2" and "2π" are wrong as the section is written "the force per unit length, Fm, that one wire exerts upon the other…": in that context, the correct figures are "1" and "4π". The factor of two comes in because there are two wires, and each exerts a force on the other. This is why the force mentioned in the definition of the ampere is 2×10−7 N, and not just 10−7 N. Physchim62 (talk) 10:59, 1 April 2010 (UTC)

More nonsense. Hint: what is the circumference of a circle? /Pieter Kuiper (talk) 11:46, 1 April 2010 (UTC)
An the surface area of a sphere? Physchim62 (talk) 16:28, 1 April 2010 (UTC)
Physchim, not that I want to sound rude, but you really ought to pick up your EM book and go through the derivations again. Yes there are two wires, but the factor of 2 comes from the integration path. Talking of the "per wire force" make no sense. The equations are right. I suggest Robert Good's Classical Electromagnetism for a clear and detailed treatment. 21:19, 1 April 2010 (UTC)
Heresy! I have to put in a plug for Griffith's text on electrodynamics, he truly is a joy to read. FellGleaming (talk) 21:38, 1 April 2010 (UTC)

## Error in Ampere's law dimension

Ampere's law is dimensionally wrong. [N] is not equal to [N/m]. Also it would be nice to explain some history, how came mu0=4pi.10^(-7), sharp? B.S. —Preceding unsigned comment added by 173.58.180.116 (talk) 20:26, 12 October 2010 (UTC)

## History and Maxwell

There is the statement:

Maxwell's laws show that speed of light in a vacuum, c0 is related to the magnetic constant and the electric constant (vacuum permittivity)...

Which, as I understand it, is historically incorrect. As I learned it, after Maxwell came up with the equations he determined that the speed of propagation of EM waves (that is, 1/sqrt(εμ)) was close to the measured speed of light, and therefore considered that light might be an electromagnetic wave. The current version makes it sound like it was derived the other way around. Gah4 (talk) 22:18, 24 January 2011 (UTC)