Talk:Magnetic field

International System of units for the field B

The B field units in the SI are described as Tesla = newtons per meter per ampere [...] in the SI. However, Newtons are a derived unit not a base unit from the SI. Wouldn't it be better if we defined the Tesla from basic units? This would give : Tesla = (kg*m^2) /(A*s^2) Leonel Gouveia (talk) 12:49, 1 June 2017 (UTC)Leonel D. Gouveia Ergin

wrong or whatever

a field is defined as force over quantity. in magnetism, the quantity is the flux, φ so H = F/φ = (Fd/φ)/d = (W/φ)/d while W/φ is magnetic potential / magnetomotive force measured in Amperes, so H (A/m). the density is quantity per area, so B = φ/A = (φ/t)t/A. the φ/t is electromotive force measured in Volts, so B (V.sec/m2). step back in electricity the quantity is charge, q so E = F/q = (Fd/q)/d = (W/q)/d, the W/q is electric potential, u. so E (V/m). the density is D = q/A = (q/t)t/A = it/A so D (A.sec/m2). in gravity the quantity is mass, m so G = F/m = (Fd/m)/d = (W/m)/d, W/m is gravitic potential, h that can be measured in Grays, so G (Gy/m). the density: J = m/A = (m/t)t/A = yt/A while y is gravitic current measured in cail/sec (Le[gendre]? ). also we can define gravitic flux, β (that is in rhyme with φ, compare: φ/t = u, β/t = h). for field we have C = F/β = (Fd/β)/d = (W/β)/d. the W/β is mechano-motive force, y so C (Le/m). it's weird but C field is exactly the dynamic viscosity and dimensionally equivalent to Pa[scal].sec, for density: K = β/A = (β/t)t/A = ht/A so K (Gy.sec/m2). the Newton law can be shown as F = mvK so K is in bond with a = vK (i.e. we can define acceleration as vK, not v/t). compare: F = qvB = φvD = βvJ (see? B is in density row. field row: u = Ed, i = Hd, h = Gd, y = Cd). for units mentioned, Gy and Le, the torque, τ and angular momentum, L can be easily measured in Gy.cail and Le.m2, while angular velocity, ω and acceleration α, shown in Le/cail and Gy/m2 respectively. (cail, c, is chilog[ram] ) {I say, we can result equivalency principle: the m in F = mvK is that in F = k_G.m₀m/r2 if the q in F = qvB is that of in F = k_Eq₀q/r2, (and for two magnets: F = φvD and F = k_Mφ₀φ/r2) (and hydrodynamics? : F = βvJ with F = k_Zβ₀β/r2) .
Tabascofernandez (talk) 23:28, 14 July 2017 (UTC)

Why it is conservative ? Bibhabasu Mondal (talk) 06:49, 10 April 2018 (UTC)

Needs to be more accessible

The subject of the "Magnetic Field" is complicated and involves a great deal of upper level math. Lots and lots of awe inspiring differential equations and integrals. In the opening "survey" paragraph of this Wikipedia article (in fact, any Wikipedia article) the discussion should be simple enough that an interested and motivated high school student can read it and come away with a decent mind's picture of what a magnetic field is. What causes one, and what it can do regarding force. The present opening paragraph doesn't do this. What good does it do for a physicist to write an article that only a physicist can, and probably already does, understand? J Devore, Philadelphia — Preceding unsigned comment added by 73.81.157.156 (talk) 21:07, 5 November 2017 (UTC)

I partly agree. This topic is just intrinsically complicated (more so than Electric field) so the introduction is unavoidably going to refer to some esoteric stuff, but as you say the introduction is supposed to be understandable by general readers, and I think it could be improved. The lead sentence:

"A magnetic field is the magnetic effect of electric currents and magnetic materials."

has always bothered me, it seems too vague. How about something like:

"A magnetic field is a force field that is created by moving electric charges (electric currents) and magnetic dipoles, and exerts a force on other nearby moving charges and magnetic dipoles."?

--Chetvorno^TALK 22:38, 6 November 2017 (UTC)

As another non-physicist I also agree. Those suggestions sound like an improvement to me but the real killer is the sentence that reads "The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter (symbol: A⋅m−1 or A/m) in the SI. B is measured in teslas (symbol: T) and newtons per meter per ampere (symbol: N⋅m−1⋅A−1 or N/(m⋅A)) in the SI." That is far too long and complicated for a single sentence and do we really need all that detail in the lead anyway? At a minimum I think we should lose all the parts in parentheses about symbols and confine those to the body of the article. Richerman (talk) 23:24, 6 November 2017 (UTC)"

Hmm, in fact I've just realised it's two sentences but they are so complcated it's hard to tease them apart. How about simplifying this to "The term is used for two distinct but closely related fields denoted by the symbols B and H, where, in the International System of Units, H is measured in units of amperes per meter and B is measured in teslas or newtons per meter per ampere". Richerman (talk) 23:56, 6 November 2017 (UTC)

Just for background, this sentence was the result of a Talk page discussion a few years ago that concluded that (1) B and H need to be mentioned in the introduction since they are the vectors representing the magnetic field and a lot of the article revolves around them, but (2) the intro shouldn't try to explain the difference between them, but just give the units they are measured in. Since this article is about a physical quantity, I feel the units need to be given in the intro, although maybe not in as complicated a form as the current sentence. Richerman's new version is better; it would be fine with me. --Chetvorno^TALK 00:37, 7 November 2017 (UTC)

I think the rewording proposed by Chetvorno and Richerman are both improvements, but a little more needs to be said about the relationship between B and H. At this point, it seems easiest to just try rewriting the first paragraph, so I have done that. I removed the note about a magnetic field being a pseudovector because I think it is too technical for the lead. The point is made in the body of the article. RockMagnetist(talk) 17:39, 7 November 2017 (UTC)

RockMagnetist's version looks good to me; if the intro is to include math, these are the minimum equations that should be included. --Chetvorno^TALK 18:03, 7 November 2017 (UTC)

Ah but, that's my main point - should we have maths in the lead at all? Famously Stephen Hawking said in A brief History of Time that he was warned that for every equation in the book, the readership would be halved, hence it includes only a single equation: E = mc2. If he can write a book on such a complex subject with only one equation then surely we can keep them out of the lead of an article so as not to discourage readers before they start. Couldn't we just say something to the effect of the value of B is different whether it's measured in a vacuum or a material due to the magnetization of the material? Richerman (talk) 18:11, 8 November 2017 (UTC)

Well, I agree it would be preferable to avoid equations in the introduction. RockMagnetist, could we explain the relation between B, H, and M in words? --Chetvorno^TALK 19:08, 8 November 2017 (UTC)

How about this: Aside from units, B and H are the same field in a vacuum, but in a material they are altered in different ways by the magnetization. 23:07, 8 November 2017 (UTC)

That sounds good to me. Richerman (talk) 23:35, 8 November 2017 (UTC)

I tried adding that sentence, but it seemed too vague, so I tried adding a little on their vector properties. I know it's more technical, but it's about the simplest way I can think of to bring in Maxwell's equations. RockMagnetist(talk) 22:23, 10 November 2017 (UTC)

I think the equation version was better. The current version gives some properties of B and H but does not say anything about their relationship, and nontechnical readers are not going to understand the terminology. --Chetvorno^TALK 20:52, 11 November 2017 (UTC)

I love the image you added, I never saw a graph of B and H for a magnet separately. The second image perfectly illustrates the Gilbert model of magnetism, representing H as sourced by fictitious magnetic "charges". It definitely should be in the article, but I question whether it should be the introductory image. I think it is more needed in the article body where the relation between B and H is explained. I feel the previous introductory image was better; even better might be an iron filings image of the field around a magnet. --Chetvorno^TALK 20:52, 11 November 2017 (UTC)

Either version is o.k. with me, although I think I too lean towards the first version. I'll wait to see what other people think. RockMagnetist(talk) 23:11, 11 November 2017 (UTC)

The remaining sentence that bothers me is: "In special relativity, electric and magnetic fields are two interrelated aspects of a single object, called the electromagnetic tensor; the split of this tensor into electric and magnetic fields depends on the relative velocity of the observer and charge." In the spirit of J Devore's complaint above, this strikes me as far too technical for the introduction. --Chetvorno^TALK 18:12, 7 November 2017 (UTC)

I think you're right. RockMagnetist(talk) 15:34, 8 November 2017 (UTC)

Took another whack at the introduction. What do you all think? --Chetvorno^TALK 22:19, 15 March 2018 (UTC)

It's more readable, but not quite accurate. Both the H-field and B-field are affected by magnetization. The B-field can be used to account for the magnetization if you express M in terms of currents. You'd have to be a masochist to that, but many EM textbooks formulate it that way. The problem is, much as users of this article would like to see a simple definition of H and B, there isn't one. They are just the fields that appear in Maxwell's equations. RockMagnetist(talk) 15:33, 16 March 2018 (UTC)

There's also that annoying business of units: in SI units, B is just proportional to H+M. RockMagnetist(talk) 15:37, 16 March 2018 (UTC)

But my wording does not say that B cannot also be used to account for magnetization, it's just that H accounts for it more conveniently.

How about "H was a field introduced to account for magnetization..."? This doesn't prescribe it's uses. I think both this and my previous wording are certainly acceptable as a prose description of H. It is consistent with the description in our Maxwell's equations article. There, the Maxwell's equations in the variables E and B are described as "the "microscopic" version of Maxwell's equations, expressing the electric and the magnetic fields in terms of the (possibly atomic-level) charges and currents present." The equations in D and H are described as "Maxwell's macroscopic equations" or "Maxwell's equations in materials". "The "macroscopic" equations separate out the bound charge and bound current...The cost of this factorization is that additional fields, the displacement field D and the magnetizing field H, are defined and need to be determined. Phenomenological constituent equations relate the additional fields to the electric field E and the magnetic B-field...". --Chetvorno^TALK 16:49, 16 March 2018 (UTC)

I guess on second thought I don't really have a problem with that statement. I think the current wording of the lead looks fine. RockMagnetist(talk) 17:01, 16 March 2018 (UTC)

While I strongly agree about simplifying the lead. Some of the changes are causing more trouble than they are solving IMO. For example the use of the term 'force field' is neither true nor enlightening or even simple. I am going to try to work on the lead some focusing on 1. keeping it simple, 2. keeping it so that it reflects what is covered in the article, 3. keeping it as complete as possible, and 4. keeping it short. I realize that these are all competing (and often contradictory) goals. I am mentioning this as a warning that my changes might make things worse before it makes them better. I will keep in contact here. TStein (talk) 17:27, 10 April 2018 (UTC)

I think some of TStein's recent changes to the introduction are improvements, others I disagree with:

• I don't like the new lead sentence: "A magnetic field is a quantity that describes the magnetic influence at a given point due to nearby electrical currents and magnetized materials." This is a step back to the type of lead we had before, a vague tautology which gives readers no information. I agree that the term "force field" in the previous lead was not very good, but I think the wording should somehow say that magnetic fields exert force.
• I like the new sentence contrasting H and B: "H and B differ in how they account for magnetization." This is better than my previous sentence, which RockMagnetist quite rightly pointed out was not really accurate.
• I like that the sentence "In everyday life,..." is moved up closer to the top, so general readers will see something they can recognise right away, amid all the strangeness.
• "Magnetic field surround and is created by magnetized material..." seems to be a grammatical mistake?

I know but I have a hard time deciding when magnetic field should be singular or plural. I am going to have to defer to others. TStein (talk) 21:25, 18 April 2018 (UTC)

• "Magnetic fields exert...torques on nearby magnets." They also exert forces on them.

My reasoning was that the force on magnets was due to difference in magnetic fields (a magnet in an perfectly uniform magnetic field experiences no force). Further, I believe that it is covered in the lead soon after. TStein (talk) 21:25, 18 April 2018 (UTC)

--Chetvorno^TALK 22:03, 11 April 2018 (UTC)

I support Brian Everlasting's reversion of TStein's replacement of the term "vector field" with "quantity" in the lead sentence. TStein's lead sentence: "A magnetic field is a quantity that describes the magnetic influence due to nearby electrical currents and magnetized materials", besides not giving any substantive information about the subject, will be misleading for general readers as it describes a magnetic field as a singular "quantity" - it is 3 quantities defined at each point in space. We define "vector field" a few sentences down in the lead paragraph, so I don't think it will be too confusing to use the correct term in the lead. ----Chetvorno^TALK 20:12, 18 April 2018 (UTC)

Chetvorno: thanks for your input. I never feel one hundred percent comfortable with any of my changes. It is an iterative process. To some extent I agree that the first sentence is 'vague tautology' but on the other hand it gives a starting point for which to add the rest of the paragraph. I believe that we risk alienating non-technical readers if we get to technical terms like vector field too quickly. My choice was to start off vague and add complexity at a reasonable pace. Other choices may work better. But, I feel that making the first sentence more vague has allowed the first paragraph to be better as a whole. TStein (talk) 21:25, 18 April 2018 (UTC)

Thanks for all the great comments. It seems to me that User:TStein and User:Chetvorno, (and everybody else) are doing a good job so far with this article. I understand the argument that this article is too technical for beginner readers to understand, but over simplification may lead to factual errors. Also, vector calculus and vector field are subjects not normally covered in high school curriculum. Further complicating the situation is the fact that some students learn "non-calculus based physics" while other students learn "calculus based physics". For a non-calculus based physics student, TStein's argument "quantity" makes more sense. So maybe we need another non-calculus based article on Magnetic Field like "Introduction to Magnetic Field", or maybe just a new section in the existing article for non-calculus based explanation? Or maybe we should list prerequisite articles at the top of this article like: "WARNING, don't read this article unless you have already read calculus, line integral, cross product, vector field". Although physics and calculus are very closely related, many concepts in physics can be explained to a high degree of accuracy without calculus. Brian Everlasting (talk) 22:01, 18 April 2018 (UTC)

Brian Everlasting: Having both a technical and non-technical version of this page is probably way too much effort to maintain and to keep distinct and to get the right audience to the right page. I believe that the best approach is to start off as least technical as possible and to build up what is needed when it is needed. A good overview can be useful for both the technical and the non-technical. Stating technical facts can sometimes serve neither user as it simultaneously confuses the non-technical user and merely restates what the technical user already knows in the same way they have heard it a thousand times over. TStein (talk) 22:55, 18 April 2018 (UTC)

Brian Everlasting: Personally, I like the challenge. Any expert can make an article near perfectly complete and correct. Any educator can make an article near perfectly accessible to the nontechnical reader. Any professional writer can make an article near perfectly concise and interesting. Unfortunately, it is impossible to do all three perfectly; perfection in any 2 comes at the expense of the third. That is why articles like this one are so difficult; it really needs to be as excellent as possible at all three. I have confidence that it is gradually getting to where it needs to be thanks to editors like you and everyone else who works on this page. TStein (talk) 22:55, 18 April 2018 (UTC)

Impressive to see the efforts to achieve the impossible. Naive query/suggestion: If the idea is to reach both technical and non-technical audiences, then maybe the "lead section" should have "technical" (presupposing physicists conceptual language/frame) and "non-technical" subsections? Or in any case to have a clear marking of when the text is being informal, qualitative, and when it is switching to using the technical language/concepts that physicists are using to explain/understand/interpret the phenomena. I can elaborate if this sounds interesting. Sdc870 (talk) 04:40, 20 April 2018 (UTC)

I know that I started it but this is in my opinion way overthinking the problem. (Just like I was overthinking the problem earlier.) TStein (talk) 15:35, 20 April 2018 (UTC)

@Sdc870: I pretty much agree with TStein. However I appreciate your viewpoint. It seems to me the introduction is already sort of divided into a "technical" section, paragraph 2, and "non-technical" section, which is the remainder. Maybe the wording of the nontechnical parts can be improved. ----Chetvorno^TALK 18:12, 20 April 2018 (UTC)

@TStein: @Chetvorno: I accept your points.

Here are some more suggestions.

1. For first sentence, add underlined: In physics, a magnetic field is a vector field that describes the magnetic influence due to nearby electrical currents and magnetized materials.

Reasons: (a) gives contrast (and uses parallel form) to next sentence, which starts ‟In everyday life”, (b) makes clear that ‟magnetic field” is being used here as a technical term, which justifies it being named as a vector field. Sdc870

I don't really think it's needed since the term "magnetic field" does not have a second usage in some other area of study, but I have no objection to the addition. Where that phrase is really needed is in the first sentence of the second paragraph: "In physics, the term 'magnetic field' is used for two distinct but closely related fields denoted by the symbols B and H." (or "In electromagnetics...").--Chetvorno^TALK 22:59, 21 April 2018 (UTC)

2. For second sentence in 1st para (add underlined, delete struck through): In everyday life, the effects of magnetic fields are most readily encountered with seen by the force created by permanent magnets, which pull on ferromagnetic materials such as iron, cobalt, or nickel, and attract or repel other magnets.

This would result in: In everyday life, the effects of magnetic fields are most readily encountered with permanent magnets, which pull on ferromagnetic materials such as iron, cobalt, or nickel, and attract or repel other magnets.

Reason: Should be obvious, but I can explain if needed. Sdc870

3. Last sentence in 1st para. seems redundant – ‟As such, it is an example of a vector field” – given that the vector field is mentioned in the first sentence. Sdc870

My feeling is that since the mathematical term "vector field" must be used in the introduction (particularly since it is in the lead sentence), there needs to be a brief description of what a vector field is, for nonmathematical readers. This sentence fills that need. --Chetvorno^TALK 22:59, 21 April 2018 (UTC)

@Chetvorno: Ok. I understand the intent now. Are you assuming that a nonmathematical reader knows what a vector is, and just needs to understand 'vector field'? Meanwhile, the referents of "As such" and "it" in that last sentence are ambiguous. Here is an attempt to address that problem by combining the two sentences: "Viewed as a vector field, the magnetic field describes the strength and direction of magnetic force for different locations within the field" (My reasoning is that even if someone does not know what a vector is, or vector field, they may be able to understand that the magnetic field describes strength and direction in different locations. (Also, take a look at the word "location" in the present formulation. If a person does not understand the field idea, then the sentence could be read as though the location of the (entire) field, rather than location within the field. Ok. I leave the rest to you. Sdc870 (talk) 04:05, 24 April 2018 (UTC)

4. Maybe sentence in third para that starts: ‟Magnetic fields are produced by moving electric charges….” should be moved up to the first paragraph and combined with the sentence that starts ‟Magnetic fields surround and are created by ...” (because they are both explaining how magnetic fields are produced). And if that happens, then perhaps the other sentence in the third para. (about interrelation of electric and magnetic field will follow along). Sdc870

I don't have any real concerns with any one of these except for including the term 'in physics'. Both the B and H fields are used by a very broad range of fields outside of physics. My main concern is that many little improvements can make the whole worse. A slightly longer and more precise word here, a little more explanation there, a little more symmetry of the sentence structure someplace else; they are all good things individually but each of those can add a little extra burden to the lead as a whole. Every artist knows that it is important to tweak to make things a little more perfect; but every artist also knows that there is a time where need to step back. Brevity, simple language, and avoiding complex terms and concepts until absolutely needed are also virtues. TStein (talk) 23:50, 21 April 2018 (UTC)

@TStein: Have I interpreted correctly, that I can try to enter some of these changes -- and then you can see how it looks? I do not think I have other proposals beyond what is already given here. Sdc870 (talk) 04:05, 24 April 2018 (UTC)

Sdc870: hehe. On wikipedia it is holier to ask forgiveness than permission. I don't own this page. Do whatever you think you need to do. Don't worry, if you were a crackpot or if you obviously did not understand the material or if you were wanted to make the page too technical I (and others) would be much more assertive. I am curious what it will look like when you are done. It would not be the first time that someone else's vision turned out to be better than mine. But there is no way to know until it is done. TStein (talk) 05:35, 24 April 2018 (UTC)

TStein: Ok. I will try some things. But it has also been informative to get responses here. And given that you and others have spent some time thinking about it, then I can get the benefit of your experience (e.g., there may be some reasons behind choices that I did not perceive). Sdc870 (talk) 03:36, 26 April 2018 (UTC)

And a new query about the first sentence. Is there a special reason for "influence" in the first sentence? Otherwise, my proposal:

A magnetic field is a vector field that describes the magnetic influence force due to nearby electrical currents and magnetized materials.

And right now the first sentence emphasizes the vector field. From a more everyday perspective, wouldn't one expect that the field is the "magnetic force in different locations (in a bounded region)"? Are there strong opinions that have already been resolved about whether the opening sentence should highlight the magnetic field as "physical phenomenon" or as "mathematical construct"? It may be possible to do both indicate both. For example:

A magnetic field refers to magnetic forces in a region of space close to an electrical current and/or magnetized materials. The strength and direction of the magnetic force for each location in the region can be described mathematically as a vector field.

This version might also address the issue discussed above in point 3. Comments? Sdc870 (talk) 03:36, 26 April 2018 (UTC)

The reason to use "influence" instead of "force" is this article discusses 3 different but easily confused vector fields: the B, the H, and the F. If we say force, that would imply that magnetic field is only F, which is not true. I also disagree with your proposal to remove vector field. Brian Everlasting (talk) 03:51, 26 April 2018 (UTC)

Brian Everlasting: I agree with not using the term force for the reason you mentioned. TStein (talk) 05:57, 26 April 2018 (UTC)

Sdc870: To add to Brian Everlasting's point, I disagree with the term 'close' because magnetic fields often extend for great distances. I know that is also a flaw in the original sentence (which I had a hand in writing) as well but IMO this makes that flaw worse. That being said, it is good that you are trying to fix the flaws in the lead not the least because it is a very difficult job. For example, if you want to cringe just google 'definition of magnetic field'. Sometimes editing a lead is like a classic physical humor routine, every attempt to avoid one pratfall seems to lead to hitting 3 others and every step seems to land on a banana peel or a rake positioned just right to smack you in the face. TStein (talk) 05:57, 26 April 2018 (UTC)

Discussion of units for B and H in lead is too heavy

Suggestion no. 2 The details and complication in the discussion of B and H and units of measurement seem too heavy for a lead section. Can the issues be stated in a more abstract form? For example (in the direction of): There are different magnetic fields (usually denoted with B and H), and measured with different units. (As I understand, the lead section is just informing what the article is about, and where the "links" in the Contents can be used to get into the details.) Sdc870 (talk) 04:40, 20 April 2018 (UTC)

I personally don't think that paragraph is too heavy. If you decide to fix it remember that one of the most asked for things on this talk page is the exact relation between B and H. I could support deleting the line that spells out the units as being to esoteric for the lead (others will disagree). I could also support changing the sentence relating B and H to the equation it describes. As a general rule equations feel a little less heavy when written symbolically out then when described in plain english. Non-technical readers may disagree, but I don't think that you will get very far in any article about magnetic fields without some comfort with equations. TStein (talk) 15:35, 20 April 2018 (UTC)

p.s. Sdc870 wrote the comment before I made the section to make it easier to find. (I hope this does not break etiquette or cause confusion.) TStein (talk) 15:35, 20 April 2018 (UTC)

@TStein: I have changed the title of this topic to better reflect that my suggestion was limited only to whether the units and their definitions should be named explicitly in the lead, given that they can be easily found in the article. My suggestion was aimed at finding a happy medium -- maybe mentioned units, but not all the technical details. Sdc870 (talk) 11:22, 21 April 2018 (UTC)

@Sdc870: I also don't think the discussion of B and H in the intro is too "heavy"; in my opinion the current wording is close to the minimum that is consistent with the requirement that the lead be an "adequate summary" of the article (WP:LEAD). I feel the units of B and H have to be included in the intro because that is a common piece of info that students and general readers come to this page for, and units are given in the lead of virtually every other scientific quantity on WP. In fact, I think that the widely used alternate units webers and gauss need to be added. --Chetvorno^TALK 19:30, 20 April 2018 (UTC)

@Chetvorno: My point was only about naming the units. Clearly a matter of taste. Perhaps not so useful for the non-technical reader. If kept, maybe that paragraph should be moved to the end of the lead section -- especially if alternative units are also added. Sdc870 (talk) 11:22, 21 April 2018 (UTC)

@Sdc870: By the way, I think most sources would not characterize B and H as "different magnetic fields". They are separate vector fields that provide alternate representations of a single magnetic field. --Chetvorno^TALK 19:30, 20 April 2018 (UTC)

@Chetvorno: Seems like an important point to correct! Should the first sentence in the second para. be something like: "The magnetic field is described by two vector fields, denoted by the symbols B and H." Sdc870 (talk) 11:22, 21 April 2018 (UTC)

@TStein: I agree that the English description of the equation in the intro 2nd para is a little clunky, I wouldn't mind it being replaced with some more general statement. However I think it's less scary for general readers than an actual equation. The late Stephen Hawking included only one equation in A Brief History of Time because he was told that every additional equation he added would cut readership by half. --Chetvorno^TALK 19:30, 20 April 2018 (UTC)

H-field

The H-field is not defined. Phrases like "there is a quantity H, which is also sometimes called the magnetic field" do not make up for a definition. — Preceding unsigned comment added by 5.55.156.124 (talk) 06:39, 5 February 2018 (UTC)

The H-field is defined; it is just not done so in an obvious location. Part of the problem is that the definition of the H field involves first defining what M is. Does anyone here have any brilliant ideas of how we can do that better? How do we make the definition of H more prominent and earlier without burdening the article too much with technical details about M? TStein (talk) 23:02, 18 April 2018 (UTC)

Possibly a mistake

I believe there is a mistake in the sentence reading: "Then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction repel one another.". It should say "attract each other" (alternatively, "wires having currents in opposite directions repel each other"). Can someone please check this? — Preceding unsigned comment added by 152.170.204.11 (talk) 22:53, 23 March 2018 (UTC)

Thanks for pointing this out. Someone had already corrected it; I expanded the statement to cover both cases and added a citation. RockMagnetist(talk) 16:54, 10 April 2018 (UTC)

A historical query

The History section seems to imply the Thomson had worked out a clear understanding of H and B by 1850. But I have the impression that there was uncertainty about whether H and B were physically different, and this was not resolved until around 1930 ([| History of IEC]). Or have I misunderstood something? Sdc870 (talk) 03:51, 20 April 2018 (UTC)

Interesting link. I wish I had more time to study it in detail. It is not unusual for there being a lag from when an idea was first proposed and shown to be true to when it is generally accepted. I have no clue if that is what happened here, though. I also find it strange that a committee would have the power to formally decide if B and H were two different quantities or not. If so it would seem historic to me. It might be worth you adding a sentence to the history section about this. TStein (talk) 15:49, 20 April 2018 (UTC)

@TStein: More than a "committee". IEC members are national representatives, usually with connections to the national laboratories responsible for standards and measurement. Perhaps better analogy is to "climate change" and establishment of a scientific consensus. (To others: I should have quoted the relevant sentence from the IEC link: "The much discussed question of the difference between the nature of the quantities H, magnetic field strength, and B, magnetic flux density, was finally settled.") — Preceding unsigned comment added by Sdc870 (talk • contribs) 10:20, 21 April 2018 (UTC)