Talk:Magnetic reluctance

Is the concept of magnetic reluctance correct?
If so, then if we take a ferrite toroid of length 1m and permeability 10000 and make in it a gap 0.1 mm wide, we will increase its reluctance by 100%. I find it hard to believe that such a gap would decrease the inductance of a solenoid wound on this ferrite core by 50%. Also, the formulas for the inductance of a long straight solenoid and a similar toroidal solenoid of the same path length indicate that these inductances will be almost identical, therefore invalidating the concept of magnetic reluctance.

which is the material which offers lowest reluctance to magnetic core and industrially which is the most cosrt effective material which offfers the laest reluctance
plz ans


 * Gak.
 * 01:58, 30 May 2007 (UTC)

Merged contents into Magnetic circuit
I merged contents into magnetic circuit. In most ways in my opinion this material fits better there. I have not redirected yet and I might not since this article remains a good stand alone article. I have left the merge tag to lead people to the main article, though. TStein (talk) 06:05, 20 May 2009 (UTC)
 * I won't redirect this to magnetic circuit page because of comments on talk: magnetic circuit. It is notable enough and it is complete enough.  Much of the material in magnetic circuits does not apply to reluctance. TStein (talk) 22:09, 11 June 2009 (UTC)

Article needs severe reworking
I used to, mostly, like this article but now it has become almost incomprehensible to me. With others around who seem to know the subject significantly better then me. I thought I would voice my objections before editing the article, though.

"Magnetic reluctance, or magnetic resistance, (SI Unit: At·Wb-1) is a property existing in all of space but is less in those materials where the microscopic causes of magnetic flux (called magnetomotive forces) reinforce each other in generating a stronger magnetic field. The value for reluctance is a scalar extensive quantity."

Magnetic reluctance is not a 'property existing in all of space' it is a property of objects including gaps. A steel bar has a reluctance, steel itself does not have reluctance. Indeed much of the rest of the article seems confuse the concept of reluctance with reluctivity. Reluctance is a property of object; reluctivity is a property of materials.

Second, I have severe doubts that 'MMF is a microscopic cause of magnetic flux' at least as has how engineers seem to define MMF. Engineers treat 'H' very different then physicists and seem to treat H as only due to the free currents and invent a ficticious idea called 'demagnetization'. If the macroscopic cause of magnetic flux was included in the MMF then the MMF would have to be large and negative for a steel bar with a coil around it. The integral around the entire loop must be NI but that is obtained by having a very large MMF in the gap with an almost equally large MMF that is negative in the steel (H = B/u_o - M which is < 0 in steel since M is much larger then B in steel).

Third the sentence about the reluctance being a scalar extensive property is unessary (for the lede) and extremely confusing to the average reader.

"The origin of magnetic circuits arises from introducing an electric field, which promotes the moving of electric current through the obstacles of electrical resistance and the impedance of free space. The resulting rotary movements of charges produce magnetic fields. Each magnetic field line is a closed magnetic circuit, and forms complete loop, as described by Maxwell's equations."

I know quite a bit about the subject at hand but this makes me sit up and say 'huh?'. Magnetic reluctance needs to explained as a concept before we even try to explain its microscopic origins. And when we do explain them we need to do a much better job then this.

"The concentration of flux in low-reluctance materials..."

More nonsence about low-reluctance materials. A long thing steel bar can have a greater reluctance than a short wide gap.

Do I need to say it here too?

"When it comes to reluctance $\mathcal R$:
 * It depends on the embedded magnetomotive forces (MMFs) comprising..."

Again, reluctance is a property of an object. It is the same no matter what the MMF is.

"*The lower a material's reluctance, less MMFs it requires to produce the same magnetic flux $\Phi$."

grr....

"*Two magnets aligned north-to-south have lower reluctance than the same two magnets with like poles held against each other."

I am not quite sure what this means since permanent magnets are hysteric in B and M and extremely non-linear. If such a statement is true, then it probably depends on how hard the magnets are.

... skipping over more reluctance of materials nonsence ...

"The product of $\mu_0$ and $\mu_r$ is the magnetic permeability of the material's physical state."

What does the term 'of the material's physical state' even mean?

"Magnetic reluctance as the magnetic analogue of electrical resistance The value of magnetic reluctance in magnetic circuits is based on real analysis not complex analysis; it is therefore not involved with the dissipation of potential energy in the magnetic field into some other form of potential energy. This is analogous to the role of resistance in an electric circuit, which is not related to conversion of kinetic energy in currents into magnetic or electric potential energies. The analogy is not related to extrinsic properties of electric circuits by which energy conversion occurs: 1) Capacitance involves conversion between kinetic and electrical potential energy (both-ways); 2) Inductance involves conversion between kinetic energy and magnetic potential energy (also-both ways)."

This paragraph is the one that confuses me the most. First there is no comparison at all with electrical resistance in this paragraph. Second it introduces real and complex analysis when the terms are not needed and confuse the paragraph. Then it really gets confusing with its discussion of potential and kinetic energy conversions. What is the point of this discussion other than to confuse? As far as I can tell the magnetic circuit model does not deal with energy at all. (The analogy with P=IV certainly fails).

Personally, I think this whole article needs to be reverted back to an earlier state when these flaws were not there. There may be something redeemable in the changes, but I don't see them. TStein (talk) 04:59, 26 July 2009 (UTC)


 * I agree. The new material addresses some more advanced topics, but doesn't quite get them right.  Better to have a clear, correct, less advanced article.Ccrrccrr (talk) 14:16, 26 July 2009 (UTC)

Need for revert
A very recent edit changed to:


 * Easily magnetized materials, such as soft iron, have low reluctance. In contrast, diamagnetic materials such as water and air have high reluctance.

That's wrong. As the lead says, it's a property of objects (extensive), not materials (intensive).

As noted above, that's one of many problems here. I'm leaning toward proceeding with a revert but am hoping to engage more discussion here first. -Ccrrccrr (talk) 02:25, 27 July 2009 (UTC)


 * The problem is not just the recent edits, many of which were mine. Most of what I wrote were straight deductions from the pre-existing material on the page. What this proves is that the original material, prior to my edits, is not enough to be well informative. The articles need to be more advanced, and at the same time it needs to be well sourced. This article was never that good. More than a revert is needed.'' Kmarinas86 (6sin8karma) 16:03, 27 July 2009 (UTC)


 * I don't think anybody would disagree with the need to improve the article. Some caution is needed making major changes based on "straight deductions" on material you are not familiar with, without consulting sources.  I think I will proceed with the revert, but I would encourage continued discussion here of the individual items. --Ccrrccrr (talk) 18:20, 28 July 2009 (UTC)


 * Here's a |link to the pre-revert version for reference in rescuing useful parts of it.--Ccrrccrr (talk) 18:24, 28 July 2009 (UTC)

List of useful stuff to recover from pre-revert version
I made an effort to read through and find what we might want to save from the pre-revert version. I have only one item:
 * Addition of Hopkinson to history...through we'd need to find out his role in the history for that to belong in the history section. The reverted version has that name in the appropriate place.  We'd only want to add it to history if we found out something about the history.

I welcome additions to this list. --Ccrrccrr (talk) 19:34, 28 July 2009 (UTC)

Relevance of this Application?
In the Application section, this is said:


 * Multimedia loudspeakers are typically shielded magnetically, in order to reduce magnetic interference caused to televisions and other CRTs. The speaker magnet is covered with a material such as soft iron to minimize the stray magnetic field.

What is the relevance? I am sure reluctance plays a role in the physics of the magnetic shielding but the connection is not clear. Perhaps a little more should be said to clarify. JDHeinzmann (talk) 03:33, 27 October 2010 (UTC)

Representation
The article states that "Reluctance is usually represented by a curly capital R, as can be displayed using such fonts as Monotype Corsiva". Reluctance is also commonly shown in Europe as a capital S, as is shown in this link: http://www.qsl.net/g4cnn/units/units.htm

Maybe someone can state this in the article? 90.214.133.198 (talk) 08:14, 2 August 2011 (UTC) Josh W.

Unit
In which unit is it measured? — Preceding unsigned comment added by 201.239.42.2 (talk) 20:47, 4 December 2011 (UTC)

Unit of magnetic reluctance
The texts of this and the magnetic circuit articles state that the unit of magnetic reluctance is the turn per henry. Consider, however, a thin toroid around which winds a coil of N turns carrying a current I. The magenomotive force through the toroid is F = NI, and the inductance of the coil is L = N&Phi;/I, where &Phi; is the magnetic flux through a cross section of the toroid. Hence the magnetic reluctance of the toroid is R = F/&Phi; = N2/L. It follows that the unit of magnetic reluctance is the turn squared per henry. Zophar (talk) 19:28, 4 February 2023 (UTC)


 * A turn isn't really a unit. It's just context that helps people understand the units.  So I would say the units of reluctance are H-1.  I don't think it's wrong to say that the unit is turns squared per henry, but I don't think that that's necessary or common.  Do you have a source that does it that way?  Otherwise I think we are required to go with what the sources say, which from memory and a quick look at a few is H-1. Ccrrccrr (talk) 01:42, 9 February 2023 (UTC)
 * This 1933 book has a table giving the units as Henry−1·turn2. More modern works like  have turns per henry fairly consistently. In my opinion, the modern rendering is more correct.  The &Phi; term in the inductance expression is not the same as the &Phi; term in the reluctance expression.  In the inductance expression it is the flux generated by a single turn.  In the reluctance expression the total flux is required.  Thus &Phi; (reluctance expression) = N &Phi; (inductance expression). SpinningSpark 15:37, 10 February 2023 (UTC)
 * The second source that you cite does not even give the definition of reluctance; it is a mass of confusion and is worthless as a source. As for your own argument, the answer is that reluctance is a property of the core and has nothing to do with the coil. Zophar (talk) 16:29, 11 February 2023 (UTC)
 * Try this source instead. There is no shortage of similar sources.  I know that reluctance is a property of the core, but to express reluctance in terms of turns and inductance is necessarily expressing it in terms of parameters of the winding. SpinningSpark 17:57, 11 February 2023 (UTC)

Contrary to what I have stated, this source considers reluctance to be, initially, a property of the coil, not the core. It calls it the "reluctance of the circuit," symbolizes it by S, derives the formula S = N/L, and states that its unit is turns per henry. The reluctance of the core ought to be R = NS = N2/L, whose unit is turns squared per henry. The source derives a formula for S for a long solenoid in terms of its physical dimensions and a factor 1/N. It deduces a similar formula for R by setting N to have a value of one. If it had set N = 1 turn, it would follow that the unit of R is turns per henry. But the source sets N = 1, making turns squared per henry the unit of R. Zophar (talk) 18:16, 14 February 2023 (UTC)


 * It seems like we have good references giving it as henry−1·turn2, as henry−1, and as ampere-turn/Wb. You are mentioning a source that makes the arbitrary choice of N = 1 to arrive at turns/henry.  That seems like the worst of the possible choices.  I could see choosing any of the others but I don't see a justification for that. Ccrrccrr (talk) 22:12, 1 April 2023 (UTC)