Talk:Oersted

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Wow- Just- wow[edit]

First the article states: "It is defined as 1000/4π (≈79.5774715) amperes per meter of flux path" Then it states: "One oersted also equals a magnetomotive force (mmf) of 1 gilbert per centimeter of flux path." and that "1 gilbert = 10/4π ampere-turns"

So which is it? "1000/4π amperes per meter of flux path" or "1000/4π ampere-turns per meter of flux path"?

The article then goes on to say that H in oersteds = 79.5774715 I/l without defining what I is (again is it current in Amperes, much like the I in V=IR, or is it ampere-turns?). And what units is l in? Meters? Centimeters? —Preceding unsigned comment added by Sirket (talkcontribs) 05:53, 7 June 2009 (UTC)

Hope this helps, http://www.walkerscientific.com/Products/FAQ/Conversions/conversions.html —Preceding unsigned comment added by 133.1.195.196 (talk) 09:55, 25 March 2010 (UTC)

I think part of the confusion may be that ampere and ampere-turn are two names for the same thing, as illogical as that sounds. According to the BIPM website "Similarly for the base quantity electric current as well as the derived quantity magnetomotive force, the SI unit is the ampere." Thus, it sounds like SI simply uses the unit amperes instead of ampere-turns when referring to MMF. If this is the case, perhaps the article should explain this situation. It seems that the second problem you describe has since been fixed. WilliamJenkins09 (talk) 05:18, 10 November 2009 (UTC)

no, amperes (symbol A) and ampere-turns (symbol At) are not the same thing. -- 99.233.186.4 (talk) 20:02, 11 January 2010 (UTC)

The confusion is between units of MMF - ampere-turns (or gilberts in cgs) - on one hand and units of H-field strength - ampere-turns per meter (or oestred in cgs) - on the other.

Ampere is a unit of electrical current whereas ampere turns is current times the number of coil turns. However, coil turns as a 'pure number' has no unit so they are both denoted A.IanOfNorwich (talk) 17:46, 12 August 2010 (UTC)

PS Not sure what constitutes expert attention but this article is now at least 'correct', so I'm going to remove the needs attention and contradiction tags. Happy to look at it again if anyone thinks it is amissIanOfNorwich (talk) 17:52, 12 August 2010 (UTC)

Simple answer[edit]

Oersted in cgs and Ampere/meter in SI are units of magnetization, and also of magnetizing-effect of currents. That may be where the confusion comes from.

A permanent magnet has a magnetization, and magnitude of that can be expressed in Oersted or Ampere/meter. Interpretation of Ampere per meter in this case comes from Ampere-model of magnetism, which basically says that a magnetic material can be thought to consist of a large number of current-loops spread throughout that material, and effect of a single such currentloop is proportional to it's loop surface and it's loop current, so it is measured in A m2, and magnetization of that material depends on strength of individual currentloops and on density of currentloops (measured in /m3), so, in this model, magnetization of a material is expressed in Am2/m3 = A/m .

This article thus correctly states that 'per meter' refers to meters along flux path.

For the other use of this unit, ie effect of a current to cause magnetization, it is in modern times known that if a current flows in a straight wire, and when the current path is closed such that the return current flows at great distance from this current, then the magnetic field is nearly completely determined by the near current and nearly not by the far current (see definition of Ampere unit for a place where this is used) (in Maxwell's time this was not yet proven). So, a current in a straight wire has a magnetic field, but it does not have any turns, so Ampere turns is simply not a usable unit for expressing magnetic field strength.

The magnetization-causing effect that a current has on a magnetizable material depends strongly on the geometry of the current relative to the magnetic material, so to compute the effect you have to compute the sum of effects of short segments of that wire. You can not simply assume that the effect of a magnetizing current is proportional to current and loop surface, because this is true at large distance compared to loop size, but is not true at short distances.

Thus the equation given in the "Gilbert" article is at best a rule of thumb, and not a law of physics. Therefore, in my opinion, the Oersted article should not refer to the Gilbert article, but the Gilbert article might refer to the Oersted article.

Additionally, this article states that in vacuum 1 Gauss equals one Oersted, but this is wrong because they have different units. It would be correct to say that, in vacuum, if the magnetizing-effect is 1 Oersted, then the magnetic field strength is 1 Gauss. Therefore i think it would be best to refer to the Gauss article, instead of stating this equality.

It is my opinion that Oersted relates to ampere-turns under assumption that the current-loop is very far away, so any use of ampere-turns where this is not mentioned is confusing and misleading.

I am now going to edit this article, to remove mention of Gilbert, and to rewrite sentence about relation between Oersted and Gauss, but i do not remove the 'self-contradicting' notice because i want more users to agree on it before it is considered fixed. —Preceding unsigned comment added by Siwardio (talkcontribs) 17:46, 20 April 2010 (UTC)

Horrible[edit]

This page is f*cked, what amateur experts have muddled it all up? —Preceding unsigned comment added by 75.164.213.1 (talkcontribs) 21:14, October 6, 2008

^ All too true, Wikipedia hasn't helped me at all with any scientific research because I find myself confused when it contradicts itself like it did on this particular page. I end up having to sift through a ton of websites to find a definition of a scientific term that MAKES SENSE.

    • But it's the Wikipedia! It's free. It's open. It's crowd-sourced. It's trendy. The Media is wetting itself covering it. How can you be dissin' the model of knowledge development? Myself, I think of Wikipedia as reliable as the guy at the next bar stool - and in a tiny fraction of Wikipedia articles you can actually find sources to back up the speculation and rumors you read here. --Wtshymanski (talk) 13:41, 7 April 2011 (UTC)

References[edit]

where is the sources that this info is from?75.4.174.74 21:55, 5 April 2006 (UTC)dave

Some of the references given now seem of dubious quality.
—DIV (128.250.80.15 (talk) 09:41, 19 April 2008 (UTC))

From PNA/Physics[edit]

  • * * * * * * *

The equation has the units Amp-turns per centimeter, but the definition has the units Amps per meter. It looks like it should be Amp-turns per meter. (198.118.127.182 20:30, 8 June 2006 (UTC)C. Raeihle, 6/8/06)

  • * * * * * * *

The Gauss (unit) article says "one ampere per meter is ten thousand oersted". This article says "One oersted equals 1000/4π, or 79.58 ampere-turns per meter". They can't both be right.

  • * * * * * * *

The Gauss_(unit) article has now apparently been corrected. At the time of this comment, it states "one ampere per meter is equal to 4π × 10−3 oersted," which agrees with this article. WilliamJenkins09 (talk) 05:28, 10 November 2009 (UTC)

Visual Ambiguity![edit]

In the statement : 1 Oe = μ G, this should be 1 Oe = μr G, to avoid confusion? —Preceding unsigned comment added by 71.164.81.99 (talk) 18:12, 22 June 2008 (UTC)

in CGS system, permeability of a vacuum is defined as 1, so yes, while it is relative permeability, the distinction is historically out of context. -- 99.233.186.4 (talk) 19:57, 11 January 2010 (UTC)

The forward-slash (division), italic captial I and lowercase l all look identical in the default font in Opera 9! Perhaps all the equations should be put in math mode.

Examples[edit]

It would be good to give an example or two to illustrate the magnitude of the unit in terms that are physically meaningful for the lay reader. For example: "on a typical jet engine ... while in a typical electric toothbrush ...". —DIV (128.250.80.15 (talk) 09:44, 19 April 2008 (UTC))

Okay, "jet engine" is probably a very bad example ...which is why I'm not editing the article. —DIV (128.250.80.15 (talk) 09:46, 19 April 2008 (UTC))
A good starting point would be the examples given in the introduction to the "Watt" article. —DIV (128.250.80.15 (talk) 02:45, 8 May 2008 (UTC))
In the article orders of magnitude (magnetic flux density) there are examples given in Tesla, so these can be converted into Oersted for this article. I'm currently too lazy to do it myself... However, maybe the link is enough because otherwise the information would be doubled. --Cyfal (talk) 05:05, 8 May 2008 (UTC)