Talk:Electromagnetic induction

Electric motors, synchronous motors, and solenoids

It's my understanding that these primarily use the magnetic field produced by the flow of current to interact directly with a permanent magnet or ferrous metal, and do not rely on induction for their operation. Is this accurate? Trevyn (talk) 22:21, 26 April 2011 (UTC)

It certainly isn't true for solenoids. 96.238.184.216 (talk) 07:15, 21 May 2011 (UTC)

Lay person's description

It would be good to have a simplified and qualitative statement of what induction is so that anyone with an interest in the topic could get the main point without having to have had any other physics. A simple definition. I would write it myself but suspect that someone else could do a better job. Something along the lines of "Induction is the process by which an electric potential (volts) in a circuit is created by a change in the magnetic field (flux)." See, I told you you could write something more accurate. In addition, you should mention in the first paragraph that induction is the principle by which electrical generators work, whether it is a simple camping generator or a power plant. Eperotao (talk) 18:45, 20 December 2009 (UTC)

Current or Voltage?

Right at the beginning of the article it says: "Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field."

However half a page down it says: "Michael Faraday formulated that electromotive force (EMF) produced around a closed path is proportional to the rate of change of the magnetic flux through any surface bounded by that path."

When you look up electromotive force it says: "In physics, electromotive force, emf (seldom capitalized), or electromotance (denoted and measured in volts) refers to voltage generated by a battery or by the magnetic force according to Faraday's Law,[...]".

You see, at one point it is current and half a page down it is voltage? — Preceding unsigned comment added by 93.204.72.164 (talk) 22:57, 15 May 2012 (UTC)

First sentence: "Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field." I would suggest changing the word "through" to "relative to", so as to not exclude the case where the conductor is stationary and the magnetic field is changing. Digging a little deeper, and drawing from another comment, a current isn't produced "across" a conductor but "along" it. A voltage is produced "across" the conductor.

So maybe "Electromagnetic induction is the production of an electric current along a conductor as a magnetic field changes relative to it." — Preceding unsigned comment added by 66.172.101.64 (talk) 22:52, 22 May 2012 (UTC)

It should be voltage. With induction here is always a voltage; whether there is a current or not depends on whether there is a closed circuit available. — DavidMack (talk) 04:14, 29 August 2012 (UTC)

Wrong symbol?

I read:

If the path Σ is not changing in time, the equation can be rewritten:

$\oint _{\partial \Sigma }\mathbf {E} \cdot d{\boldsymbol {\ell }}=-{\frac {d}{dt}}\int _{\Sigma }\mathbf {B} \cdot d\mathbf {A} .$

The surface integral at the right-hand side is the explicit expression for the magnetic flux Φ_B through Σ.

I think that should be:

If the path ∂Σ is not changing in time [...]

Why?

There is still no information why a changing magnetic field induces a voltage. And why a static magnetic field does not. — Preceding unsigned comment added by 94.197.127.240 (talk) 05:35, 20 May 2013 (UTC)

You have been waiting a while for a response. I am afraid that my answer will not be satisfying. In general, scientific theories never tell you why an effect occurs. Sometimes, we can mathematically derive a new effect from a well-known effect and if you accept that well-known effect as true, you may feel that you know why the new effect occurs. But if you look critically at the well-known effect you realize that you don’t know why it occurs either, but you believe it because it is familiar. You may find the article Magnetic potential to be helpful. In a more direct response to your query, I would refer to the Feynman Lectures on the topic of magnetic vector potential where Feynman defines a “real” field as a set of numbers defined at a point in space that allow the computation of the forces on a particle at that point without needing to use action at a distance. In other words, fields do not cause anything; they are simply computational artifices. You may regard both the changing magnetic field and the voltage as arising together from the same cause which is ultimately the activities of charges and currents at a distance.

preceding comment by me. I forgot to sign.Constant314 (talk) 20:06, 19 January 2014 (UTC)

Although it is usual in teaching electromagnetism to start by taking some electromagnetic law or other as a given and treat it as an axiom from which the others can be derived, actually, ultimately, all magnetic phenomena are derived from relativity. The magnetic field naturally arises as a "foreshortening" of a static electric field when seen by an observer in an inertial frame moving with respect to the static field. For there to be an effect at all something must be in motion since two different inertial frames must be involved before magnetic effects arise. SpinningSpark 01:08, 20 January 2014 (UTC)

There was a time I would have thought so too. But here is what Feynman has to say in The Feynman Lectures on Physics, Volume 2, chapter 26, section 1, last paragraph, beginning with the first sentence “It is sometimes said, by people who are careless, that all of electrodynamics can de deduced solely from the Lorentz transformation and Coulomb’s law. Of course, that is completely false. ... there are several additional tacit assumptions ...”Constant314 (talk) 03:55, 21 January 2014 (UTC)

I should, of course, have specified classical electrodynamics; QED is also required for a complete picture. I did not actually say that only the Lorentz transformation was needed, but whatever else needs to be assumed, it is still true that none of the laws of Faraday, Ampere, Maxwell etc are postulates that need to be treated as axioms. They can all be derived. In any event, my statement remains a correct answer to the original question of why a static field does not give rise to electrodynmic effects in the absence of motion and it is a better answer than saying because Faraday's law says so. SpinningSpark 12:52, 21 January 2014 (UTC)

Francesco Zantedeschi and Joseph Henry in the lead.

The claims that these two men may have discovered electromagnetic induction seem too weak to be in the lead. We might say something the body of the article but not in the lead. Martin Hogbin (talk) 17:33, 27 February 2014 (UTC)

I am tending to agree with you. I had never heard of Zantedeschi and the source cited is very vague. I do not understand how such a setup can possibly induce a current (according to the source Z. had a copper wire fixed between two poles of a magnet - i.e. no dynamic element). I also note that the claim is in a section of the source dealing with mistaken and false results so it is quite unclear to me if even the cited source is supporting this claim. Henry has more of a case but the NNDB can hardly be considered a high quality source. According to this book, which is rather more authoritative, says that the consensus is to give priority to Faraday for mutual induction and Henry for self induction, although Henry independently found both effects. SpinningSpark 22:14, 28 February 2014 (UTC)

See my proposal below. We do have two distinct subjects and if we unmerge the two articles we can more properly give due credit. Martin Hogbin (talk) 11:39, 4 March 2014 (UTC)

Proposed demerger

The page Faraday's law of induction currently redirects here after a merger. I propose that we unmerge the two articles. Electromagnetic induction is a general subject covering self-inductance. Faraday's law of induction is one of the most important laws of Electromagnetism. I think it should have its own article. Martin Hogbin (talk) 11:37, 4 March 2014 (UTC)

I agree with that, I had considered doing that myself after following a link to Faraday's law and finding this Easter egg. Faraday's law (of induction) is bound to be a popular search term (in the context of this subject) and we should give readers the article they are expecting rather than a surprise. SpinningSpark 12:47, 4 March 2014 (UTC)

FyzixFighter also agrees with the demerger. I suggest we wait a while to see if there is any objection and, if none, make the split. Martin Hogbin (talk) 13:02, 4 March 2014 (UTC)

Could you elaborate on the demerger. I think Faraday's law applies to self inductance as well as mutual inductance. Constant314 (talk) 15:22, 4 March 2014 (UTC)

Of course, Faraday's law applies to everything with a time-varying magnetic field but it is a specific mathematical law and one of Maxwell's equations. As such it must rank as one of the most important equations of classical physics and fully deserving of its own article in WP. Have a look at the Maxwell's equations article and you will see that the four equations all link to individual articles, except that Faraday's law is a redirect. The article on this subject should concentrate on the mathematical law and its applications.

Electromagnetic induction is the name for the general phenomenon of short range electromagnetism. This article could be more general and rather more practically based and also give more of the historical perspective.

Another advantage of having two different subjects will be that it will be easier to show the contributions of individual scientists. Henry, for example certainly did important experiments in the subject and is generally credited with the discovery of self-inductance but I do not think he contributed significantly to the formulation of Faraday's law. Martin Hogbin (talk) 17:13, 4 March 2014 (UTC)

Sounds good. I have no objection. Constant314 (talk) 17:46, 4 March 2014 (UTC)

Sounds good. But unless you want to split Maxwell-Faraday from Faraday's law, it isn't good. There is only one topic. There isn't anything more general.GliderMaven (talk) 19:35, 5 March 2014 (UTC)

I support demerging. But I would like to note that this article uses very careful language and I would hate to lose that. I can only imagine the battles that must have been waged to reach this state. Constant314 (talk) 02:31, 5 March 2014 (UTC)

As someone already noted, I would support a demerger. Note that, until about a year ago, there were two separate articles and I'm not seeing any major debates over wording since the merger. I was honestly surprised when another editor merged the two despite my objections a year ago and despite no other editor commenting either for or against. Because a lot of the material was nearly cut-and-pasted from the other article I think doing a surgical demerge should be fairly easy without harming too much of the careful language which for the most part pre-dates the merge. I do think that the merge helped move some sections over that were awkward at the Faraday's Law article (like the applications and discussion of eddy currents and parasitic induction - whether they actually belong here is another discussion). --FyzixFighter (talk) 04:18, 5 March 2014 (UTC)

Can I suggest that we start by copying this article to the Faraday's law page. I suggest we then remove everything on that page which is not directly about Faraday's law or the Maxwell–Faraday equation.

On this page I suggest that we summarise Faraday'law to one section with a 'main article' link. Martin Hogbin (talk) 09:14, 5 March 2014 (UTC)

That sounds OK to me. Constant314 (talk) 18:54, 5 March 2014 (UTC)

Strongest possible oppose

Once you split them there's nothing left. Check out the original article here: [1] It's little more than a stub, but I tried to expand it, but couldn't think of anything to add to the Electromagnetic induction article, and none of the above discussion has found anything either. There isn't anything else.

Doing the demerge is obvious, but doesn't get you anywhere. It's not like there's multiple theories about how electromagnetic induction works. What else is there to say? There's Faraday's law, Maxwell-Faraday and that's it.

There's just not enough material for two articles. GliderMaven (talk) 19:32, 5 March 2014 (UTC)

There is strong consensus for an article on Faraday's law, in line with the articles on the other of Maxwell's equations. I would say that there will also be enough for a,less technical, article on electromagnetic induction as a general topic. We could add more on practical and historical aspects of the subject. If it still turns out that we do not have sufficient for this article then we should drop the Electromagnetic induction article. Martin Hogbin (talk) 19:47, 5 March 2014 (UTC)

There is not consensus to do this. Consensus occurs when you've resolved the issues; like the fact that you're trying to do a WP:CFORK of the article.GliderMaven (talk) 15:08, 6 March 2014 (UTC)

There is nothing to stop us having a simplified section on Faraday's law on this page with a 'main article' link. Many WP pages have overlapping content. Martin Hogbin (talk) 19:58, 5 March 2014 (UTC)

We know how that ends up. You end up with a stub article that contains nothing' except a link to Faraday's law. There's really only one topic here. You can't say 'oh I want an article on Faraday's law and another article on Induction', because there is nothing else.GliderMaven (talk) 20:13, 5 March 2014 (UTC)

You could say that we should only have articles on Maxwell's equations and the Lorentz force law to cover electromagnetism in WP but we do not do that. There are other things that could go in this page: history, technology, applications. If there really is not enough, then we can drop this page. Martin Hogbin (talk) 22:10, 5 March 2014 (UTC)

Unlike this article, that would be one impossibly big article! But the history, technology and applications you refer to apply equally well to Faraday's law; they are the history, technology and applications of Faraday's law. There's no sensible argument to be made for two articles there.GliderMaven (talk) 22:41, 5 March 2014 (UTC)

But if you want to 'drop' this article by renaming it to 'Faraday's law' I personally would have absolutely no problem.GliderMaven (talk)

As there is a consensus to have two articles I am going to copy the contents of this article to the 'Faraday's law of induction' article and then remove parts of both as a start.

If, after editing of both articles has finished, you think the 'Electromagnetic induction' article has no worthwhile content you can propose it for deletion. Martin Hogbin (talk) 08:56, 6 March 2014 (UTC)

You don't have consensus to do a WP:CFORK/POV FORK.

The mistake you've made is thinking that Faraday's law doesn't have its own article, but this is that article! Just because it's called 'electromagnetic induction' doesn't mean that Faraday's law is not the topic! There's a big difference between the name and the topic. How can I point this out any more clearly? We don't do name based articles in Wikipedia. That's dictionaries. In encyclopedias there's a topic (in this case Electromagnetic induction/Faraday's law), and you cover the topic as completely as possible.GliderMaven (talk) 15:08, 6 March 2014 (UTC)

I don't see any evidence that that is an accepted principle on Wikipedia (or even encyclopaedias in general). We have numerous pairs of articles on a named law and the thing the law is about. Some examples: Ohm's law/resistance, Coulomb's law/electric charge, Newton's law of universal gravitation/gravitation, second law of thermodynamics/entropy, Zipf's law/rank-size distribution. Can you point to a guideline that says we should not do name-based articles? Or a respected style guide that says encyclopaedias should not include them? SpinningSpark 15:32, 6 March 2014 (UTC)

That would be WP:Wikipedia is not a dictionary. Check out the table. I'd have to look at the other examples but most of the examples you give aren't the same, resistance and Ohm's law are different; Ohm's law is a linear approximation. Gravity is different to Newton's law, because Einstein's gravity etc. In some cases you have to split because the articles get too big, but it's best not to if you can avoid it. In this case Faraday's law of electromagnetic induction and electromagnetic induction are just two phrases for the same thing.GliderMaven (talk) 16:53, 6 March 2014 (UTC)

I really cannot see the problem. "Faraday's law of electromagnetic induction" is a mathematical law, "electromagnetic induction" is the process to which the law applies. 'Motion' is not the same thing as 'Newton's laws of motion'. Martin Hogbin (talk) 17:42, 6 March 2014 (UTC)

Yes. Trivially so, but only trivially. You've described the entire difference in one sentence, and one sentence is all you need. When you only need a single sentence to differentiate them, then for the purpose of writing an article they're the same topic, so it's then a content fork.

If you needed more info in one article than the other you could subarticle, but you don't, you need exactly the same information in both.

That's the problem, unlike Newtonian mechanics and motion they're one topic.GliderMaven (talk) 18:34, 6 March 2014 (UTC)

Unmerge started

I have started the unmerging process as discussed. I have stopped to see what others think but I suggest that the section of Faraday's law is reduced to a less technical summary. Martin Hogbin (talk) 09:18, 6 March 2014 (UTC)

I was a little concerned to see large chunks of the article deleted without explanation. I have not read through all the editing carefully and much of it seems to still exist in one article or the other, but better use of edit summaries is called for when doing such radical surgery. A clear indication of what has been moved and where to, and what has been deleted altogether and why. I am particularly concerned that the section on the relationship between Faraday induction and relativity has been removed. This may not have been a very good piece of encyclopaedic writing, but the subject is important. The relationship between relativity and electromagnetism is generally important and it is historically important as the path leading Einstein to the Special Theory. SpinningSpark 10:02, 6 March 2014 (UTC)

Sorry if my edit summaries were not clear enough. The removed sections are unchanged in the restored Faraday's induction law article because I do not think that they belong here now. I would not object to brief summaries here though. As discussed, I suggest that we replace the 'Faraday's law' section with a less technical summary.

I also suggest that we expand the history section here a little with separate sections on Faraday and Henry. We should add Induction cooking to the applications section. — Preceding unsigned comment added by Spinningspark (talk • contribs)

Look, this is madness. For one example how are you going to handle the history section? You either duplicate the section, but that's a complete duplication, or you try to put a quick summary in Faraday's law, but then it's out of context and unreadable, or you don't bother and just have nothing and point to the electromagnetic induction article. But then Faraday's law article is not self-standing you would have to jump backwards and forwards. None of these things work!

And the material on Faraday's law equation is currently exactly the same. How is that ever going to diverge?

I know you mean well, but at the end of the day, this is a POV fork. You're trying to pretend that there's a difference between knowledge of electromagnetic induction and Faraday's law. But the physical knowledge of electromagnetic induction is Faraday's law.GliderMaven (talk) 15:27, 6 March 2014 (UTC)

When I think of induction, I think of near field coupling such as in transformers, induction heating and dynamic microphones. Faraday’s law applies everywhere including the far field. In addition, when I think of induction, there is always a source and a recipient. That is, if there is induction, then something is being induced upon, like a transformer secondary. Faraday’s law, on the other hand is just a path integral that could very well be in free space with nothing induced on anything. So, yes, I think that there is more to Faraday’s law than just induction.Constant314 (talk) 16:02, 6 March 2014 (UTC)

The full title is Faraday's law of electromagnetic induction. so how exactly do you claim you separate Faraday's law from electromagnetic induction? To be precise the Maxwell-Faraday law applies to free space, and even then the electric field of the electromagnetic field is induced; it's still electromagnetic induction. This is the problem, both articles need exactly the same sets of information. That's why it's an ongoing CFORK.GliderMaven (talk)

We have already discussed that. You cannot say that we cannot have a separate article on electromagnetic induction just because it is fully mathematically described by the Maxwell-Faraday law.

The 'history' section is one of the reasons for the split. 'Faraday's law' is all about Faraday. Other physicists, such as Henry, should be included in the more general article. Where would 'Induction cooking' fit under 'Faraday's law'? Martin Hogbin (talk) 17:49, 6 March 2014 (UTC)

Nothing you've said makes any sense. This is not an article about Faraday. We have an article on him. Induction cooking is an application of Faraday's law, we could certainly split off applications if you want, but we can't split off Faraday's law from electromagnetic induction, we cannot have a worthwhile article on electromagnetic induction without stating Faraday's law.GliderMaven (talk) 20:11, 6 March 2014 (UTC)

I have chopped some content out of the 'Faraday's law' section but I suggest that it is rewritten less technically. Martin Hogbin (talk) 18:03, 6 March 2014 (UTC)

You're removed Faraday's law from the Electromagnetic induction article???? And expected others to fix your damn mess? Where do you get off doing this kind of thing?GliderMaven (talk) 18:50, 6 March 2014 (UTC)

I support unmerging. To allay GliderMaven's concern, I suggest that we spend extra effort writing new good content (including the extra history, and the applications like induction heating, inductors, etc.) to make sure that Electromagnetic induction is a nice article and not just a little stub. :-D

GliderMaven: I think everyone agrees that Faraday's law will be stated and described in this article, but not in excessive depth, and with a "main article:Faraday's law" link. --Steve (talk) 19:00, 6 March 2014 (UTC)

Martin Hogbin just deleted it entirely. Because of that alone I have undone it at at least temporarily. Martin Hogbin started to do it, but then hit one of the roadblocks and just completely removed material. The thing is, there isn't any good summary of Faraday's law, you either state it or you don't. I'm sorry, but there is no way to do this well.

There is no rule that says that an equation needs its own article; but there is a rule against content forking.GliderMaven (talk) 19:13, 6 March 2014 (UTC)

GliderMaven, I have not deleted anything. All the original content is there, split between the two articles. There is a reduced version in this article with a main article link. Please do not edit war against the clear consensus to have two articles. Martin Hogbin (talk) 19:56, 6 March 2014 (UTC)

You've completely deleted Faraday's law from the electromagnetic induction article. You presumably did that because you've now realised that it had to be in there (for readability), and cannot go in both places (because it becomes a CFORK) if the article is split.

I also cannot understand how the history of electromagnetic induction/Faraday's law can be split between the two articles. You simply cannot ride two horses like that.GliderMaven (talk) 20:03, 6 March 2014 (UTC)

This is the 'Electromagnetic induction' article and here is Faraday's law. Martin Hogbin (talk) 20:08, 6 March 2014 (UTC)

So where does Henry's work fit in "Faraday's law"?

In the history section where the reader would expect it to be. I hope you're not trying to create a POV fork just to exclude Henry.GliderMaven (talk) 20:23, 6 March 2014 (UTC)

Steve, I agree, let us try to make this article as good as possible although it is already more than a stub. Do you agree that the "Faraday's law" section should be less technical? Martin Hogbin (talk) 20:05, 6 March 2014 (UTC)

Proof of Faraday's law

There seems to be a circular argument going on here. The section purports to derive Faraday's law from Maxwell's equations. But one of Maxwell's equations is a vector field version of Faraday's law. Hardly a proof. Faraday's law is derivable, but that requires Special Relativity and application of the Lorentz transform to do so. At the very least the section needs renaming. SpinningSpark 10:02, 6 March 2014 (UTC)

I suggest that we continue this discussion at the Faraday's induction law article. Martin Hogbin (talk) 11:19, 6 March 2014 (UTC)

Did you even look at the proof? Or read the article?

Physicists use the words "Faraday's law" to refer to two different laws. In this article, one law is called "Maxwell-Faraday equation", and the other is called "Faraday's law". It has been that way for several years now but you should be aware that the terminology is not standardized. (For all I remember I might have made up the term "Maxwell-Faraday equation"!) For example, Griffiths and Feynman use "Faraday's law" and "the flux rule" in place of "Maxwell-Faraday equation" and "Faraday's law". But anyway: Using two different terms is essential because they are certainly two different laws, whatever we call them.

Anyway, the "Maxwell-Faraday equation" is one of Maxwell's equations, but "Faraday's law" is not. The latter states "The electromotive force around a loop of thin wire (which might or might not be moving or deforming) equal the time-derivative of magnetic flux". Therefore it includes "motional EMF" (which arises from the Lorentz force), in addition to "induced EMF" (which arises from the Maxwell-Faraday equation). Granted, "motional EMF" in one frame may be "induced EMF" in a different frame. Nevertheless, if you're stretching or deforming the wire loop, there is no frame in which the loop is stationary--the Lorentz force law is always playing a role.

So, the proof says that combining the Maxwell-Faraday equation with the Lorentz force law, you can prove that Faraday's law is true. It is not circular logic. --Steve (talk) 18:48, 6 March 2014 (UTC)

Proposed page move to 'Faraday's law'

It doesn't look like separating the two articles between Electromagnetic induction and Faraday's law is ever going to work. 100% of electromagnetic induction follows Faraday's law. So I propose we simply keep the merge of the two and move it to Faraday's law. Faraday's law and Maxwell-Faraday and their consequences covers everything known about induction; it's a cleanly defined topic. Subarticling Faraday law from here doesn't seem to work, there's too much overlap you end up with a mess.

If you really, really want to you could split off applications of Faraday's law to deal with generators and eddy currents and so on.

Seems to me that Faraday's Law is the WP:PRIMARYTOPIC so we merge there. Yay or nay?GliderMaven (talk) 19:56, 6 March 2014 (UTC)

You have stated several times that Faraday's law and Maxwell-Faraday and their consequences covers everything known about induction and I do not disagree but that does not mean that we should not have two articles. IT is not a content fork or anything else like that it is simple separating the mathematical law of physics from the general topic and its many uses and applications. There never was a consensus to merge in the first place, it seems that you are the only one who wants to do this so please do not edit war against consensus. Why not wait and see how this article turns out. Martin Hogbin (talk) 20:02, 6 March 2014 (UTC)

Thank you, if you do not disagree that it covers everything, then that means that Faraday's law is the primary article and electromagnetic induction is the subarticle (if it's even needed, which it probably isn't.) GliderMaven (talk) 20:26, 6 March 2014 (UTC)

It means nothing of the sort. Is all of Newtonian mechanics to be subarticles of Newtons Laws. Everyone else seems to understand and agree. Faraday's law of induction covers the mathematical law and closely physics theories of physics - it is mainly a theoretical article. Electromagnetic induction covers the subject in general including its history, notable physicists and engineers in the field, applications, and uses. Martin Hogbin (talk) 21:05, 6 March 2014 (UTC)

No, what you're doing is a CFORK/POV fork into Faraday's law, and then not properly cover Faraday's law in the Faraday's law article either. If you can explain what on earth you're actually trying to do, then perhaps we can help you, but we're not going to help you do a CFORK.

Try again; what is the scope of each article supposed to be?GliderMaven (talk) 21:39, 6 March 2014 (UTC)

(edit conflict) I think that a split in this way can work. But I wouldn't start it in the middle of such a heated discussion. I suggest to leave the two articles in their original state for a few days, everybody have a cup of tea, wait for more input from the people notified via WT:Physics, and maybe use the time to prepare the split version in user space. After that we'll be in several ways better prepared to make a decision. — HHHIPPO 21:56, 6 March 2014 (UTC)

HHIPPO, I am not sure what you mean by leave the 'two articles in their original state for a few days'. There were originally two articles until GliderMaven, with out any kind of consensus, in fact only opposition, merged them. I proposed splitting them again here and this proposal had the support of four other editors, making a total of five for the split with only GliderMaven opposing it. I therefore made the split. Since then, having failed to persuade any of the editors supporting the demerge to change their mind, GliderMaven has resorted to edit warring against the clear and strong consensus.

I would welcome input from others but until the consensus changes the article should stay demerged. Martin Hogbin (talk) 23:24, 6 March 2014 (UTC)

What I meant by "original" is "before the current edit war". It seems that wasn't the best wording, sorry. Anyway, it doesn't really matter which version we use as the temporary solution. Anything not in the middle of a rearrangement will do. The idea is just to have something useful for people to read while we're discussing and performing a rearrangement. The choice of the temporary version is no prejudice whatsoever regarding the decision on the final arrangement. Even with full consensus it would make sense to develop any large rearrangements in user space or subpages, so we hide most of the mess from innocent readers. — HHHIPPO 07:31, 7 March 2014 (UTC)

I think they are both useful as I left them. Of course, they could both be much improved and I hope that we can all work together towards that. Martin Hogbin (talk) 16:42, 7 March 2014 (UTC)

If you edit it again now, you will be 3RR and get blocked.GliderMaven (talk) 23:38, 6 March 2014 (UTC)

In Wikipedia there is a difference between consensus and majority. If I have valid points, then majority is not sufficient unless you have addressed them. In fact you, did the opposite, you completely removed the simplest version of Faraday's law from this article entirely.

How is it we need to do this precisely now? Did I introduce any falsehoods into Wikipedia? No, I'm sure I did not.GliderMaven (talk) 23:38, 6 March 2014 (UTC)

I absolutely want anybody else to comment on this. I hate, hate, hate the way that Hogbin is trying to edit war this through.GliderMaven (talk) 00:13, 7 March 2014 (UTC)

I support GliderMavenn's temporary reversion of the demerge. Martin Hogbin, I support the demerge in general, but you are changing it so fast that it is hard for me to follow. Constant314 (talk) 00:27, 7 March 2014 (UTC)

No need for a 'temporary' reversion, but Martin should make a better use of edit summaries. When it popped on my watchlist I was WTF is going on here, MH usually isn't a vandal... then I realized stuff was being moved to the other article, rather than simply deleted outright. Let's separate the topics, and then we can easily see what's missing / what's superfluous in each article. Headbomb {talk / contribs / physics / books} 02:19, 7 March 2014 (UTC)

While I have no problem in principle with demerging I honest-to-goodness have no idea how he thinks these two topics are different or what the criteria is for the move.

For example this equation has vanished from this article:

${\mathcal {E}}=-N{{d\Phi _{B}} \over dt}$

and I don't know why, but the maxwell-faraday equation is still here.

Apparently Hogbin thinks that none of the 'applications' use the Faraday equation, so that's why they're in this article? Eddy currents and jumping rings have nothing to do with Faraday's law?

Perhaps there's some different equation for electromagnetic induction other than he Faraday equations? But I'm not aware of any at all. Another view was that one was far field and the other near field, but so far as I know they're both exactly the same equations (far field in an electromagnetic wave, near field for most electromagnets), and certainly electromagnetic waves can magnetically induce currents in loop aerial.

So what is the criteria then? GliderMaven (talk) 03:26, 7 March 2014 (UTC)

Like I mentioned on my talk page. the key point is that EM induction is concerned about the phenomena of induction (i.e. how it was discovered, where it's applied, how it's used, etc.), while Faraday's law is the mathematical treatment of this phenomena (who made contributions to the understanding of induction, the mathematical details, how it relates to the Maxwell equations, how it's analogous to other physical laws, etc...). There is some overlap between the topics since one's the phenomena, and the other is the mathematical treatment of the phenomena, but that is no different than e.g. Newton's law of gravitation vs gravitation. Headbomb {talk / contribs / physics / books} 12:13, 7 March 2014 (UTC)

Sorry if I have confused people with my editing. Everything in the original article should be in the two articles somewhere. I have tried split the content exactly as discussed. All of the maths of Faraday's law and Faraday-Maxwell is in the Faraday's law of induction article complete with 'Proof', Counterexamples and 'Relativity'. That is pretty much all it should, in my opinion, contain,

In this article, I removed 'Proof', Counterexamples and 'Relativity' as being too technical and also some of the Faraday's law maths as a start to having a non-technical summary here. That is pretty much what was discussed and agreed (apart from Glider Maven) above. All the applications are in this article. Martin Hogbin (talk) 16:27, 7 March 2014 (UTC)

GliderMaven I know perfectly well that the maths behind eddy currents and jumping rings is based on Faraday's law but that does not mean that we must have a full mathematical description of the law, in all its different forms, in the article. You have had several editors explain that there are many other subjects that are split this way, Newton's law of gravitation vs gravitation is just one example. You have not answered my questions though. Where to we put Henry's contribution to the subject in an article called Faraday's law? As far as I know he did not contribute to that particular mathematical law, but he did contribute to understanding of the subject in general. Martin Hogbin (talk) 16:36, 7 March 2014 (UTC)

It's not even an important question. He is actually notable in the context of Faraday's law/electromagnetic induction, IRC most treatments do mention him. You're also taking the title much, much too literally. An article in Wikipedia doesn't necessarily cover only the title, it covers whatever the article says it covers at the beginning. The article on Gliders used to cover sailplanes (only), and switched to covering all heavier than air unpowered aircraft and... The point is the title didn't change, not for a long time (eventually it became a disamb page), and this is normal. You just have to say what it is you're covering. An article called 'Faraday's law of induction' is perfectly allowed to cover everything about electromagnetic induction provided you state that upfront.

And as I have already pointed out, your point about 'Gravitation' is not actually true. The article on Gravitation is a very general article on gravity, including general relativity and it fairly and squarely subarticle's Newton's law of gravitation. The scope of the Gravitation article is much, much bigger.

But in this case, here, the overlap in scope is complete. It really is a CFORK/POV Fork of the self-same material. GliderMaven (talk) 18:28, 7 March 2014 (UTC)

Wikipedia/Encyclopedia's don't, ever, have that kind of breakdown between articles.GliderMaven (talk) 18:28, 7 March 2014 (UTC)

And the way it works is that you only split things into subarticles when you have to; and we 100% know that our merged article is not very big. You might use subarticles if there's a long proof, but there isn't one.GliderMaven (talk) 18:28, 7 March 2014 (UTC)

This article

So what is wrong with this article as it is now and how do we fix that (apart from reverting to its original form). Martin Hogbin (talk) 16:45, 7 March 2014 (UTC)

My first suggestion is that the Faraday's law section should be rewritten to be less mathematical and more understandable to the layman. Martin Hogbin (talk) 16:47, 7 March 2014 (UTC)

I think there should be at least one equation showing that if the path is N identicle turns then the voltage is N times the path integral of one turn.Constant314 (talk) 17:00, 7 March 2014 (UTC)

I agree that is just the kind of thing that we should have here. What about trying to turn some of the maths into words? Martin Hogbin (talk)

How about you first tell us what is actually supposed to be different about these two articles? What is the actual difference in scope??? Both articles need the equations, and both articles need the history of the equations and physics.GliderMaven (talk) 18:28, 7 March 2014 (UTC)

I and several others have told you many times. One article Faraday's law of induction covers the theoretical physics, all the equations, 'Proof', Counterexamples and 'Relativity' and is liked to from Maxwell's equations. Maybe it should have a little on the history of how Faraday came to propose the law and how it became the Faraday-Maxwell equation.

This article can cover the general concept, a summary of Faraday's law for the layman, some practicalities and applications, the history of the whole subject, including Henry, and maybe even Francesco Zantedeschi should get a brief mention if we can find a good source. I am a physicist so I do understand that the Maxwell-Faraday equation classically describes all this stuff theoretically very well and I certainly would not want to see this important law of physics not given its proper prominence within WP, but that does not mean that I would expect absolutely everything that has any connection with the law to be in the one article.

I know you disagree with this but I think it is now six editors who disagree with you and no one supports your point of view. Your opinion that WP policy supports this view is also unique to you. Why not work with everyone here to ensure that both articles are as good as they can be? Martin Hogbin (talk) 18:50, 7 March 2014 (UTC)

I too have formal training in Maxwell's equations and Faraday's law. I actually solve Maxwell's equation for a living. But unlike you apparently, I actually also know how encyclopedia's work. The point of an encyclopedia is to have one article that completely covers each entire topic.

Not one article that leaves bits out, and then another copy with the same scope with a few filled in details.

That's a CFORK/POV fork. CFORK/POV forks are effectively banned in Wikipedia. It simply is not done to do that.

Sure, you could write an 'introduction to electromagnetic induction' article if you want. In most cases few people would read it though.

So, hey, I've a better idea, why not actually try to write an encyclopedia article about this topic since this is an encyclopedia??? GliderMaven (talk) 20:55, 7 March 2014 (UTC)

What is wrong with it is that you've WP:Content forked it.

You're only really allowed to break up articles when they get too big. This one hasn't got too big, it's been split for POV-type reasons.

The WP:Content forking policy says: "The generally accepted policy is that all facts and major points of view on a certain subject should be treated in one article."

The reasons for the rule include that forking creates duplicate information that can get out of date, and out of step, because people create two articles as a way of disagreeing with other material, and because it makes it significantly harder for the readers to find the right information in the first place. Wikipedia is primarily a reference work, not a textbook.GliderMaven (talk) 22:00, 7 March 2014 (UTC)

It's very, very easy to accidentally edit the wrong article.

As an example, if I go to the Faraday's law of induction article and I read the history, I don't get the full history. The rest of the history is in the electromagnetic induction page. The article doesn't reference the other article either.

While you could fix that particular problem, the rule is that you don't, you're supposed to merge the two articles together properly and cover it all in one place.GliderMaven (talk) 22:00, 7 March 2014 (UTC)

I don’t think there is a point of view fork here. No one is saying Faraday’s law is wrong or doesn’t apply. No one is disputing the facts. There is a dispute about which facts belong in each article. There may be a fork regarding target audiences, but I think that is allowed. If all the relevant facts were to be covered in one article, Faraday’s law, electromagnetic induction and Lenz law ought to be merged with magnetic vector potential. I think there is a clear distinction between the two articles. Electromagnetic induction happens in the real world. Transformers, induction motors and induction heaters all work whether there is an equation that describes them or not. Faraday’s law is part of a theory that happens to do a pretty good job of describing induction. That same theory does a pretty good job explaining the propagation of radio waves, radar reflections and wave guides.Constant314 (talk) 22:48, 7 March 2014 (UTC)

No, as defined right now at the top of the article: "Electromagnetic induction is the production of a potential difference (voltage) across a conductor when it is exposed to a varying magnetic field", that's simply a restatement of Faraday's law. You don't get to have two different articles on the same topic in Wikipedia.GliderMaven (talk) 23:12, 7 March 2014 (UTC)

Maybe I misunderstood then. I was presuming that the other article was going to be massaged into the Maxwell–Faraday Equation article. Constant314 (talk) 02:07, 8 March 2014 (UTC)

Perhaps it could be. Despite my recent heavy editing I am not trying to lay down the law about these two articles. Personally I cannot see what is wrong with having a simple qualitative statement of what EMI is at the start of this article and having a more detailed qualitative and quantitative description of the same law in the 'Faraday's law article'. THis is very common in WP.Martin Hogbin (talk) 09:56, 8 March 2014 (UTC)

My understanding from the early discussion was that Faraday’s law was only one of Maxwell’s equations that did not have its own article and Faraday’s law of induction (FLI) is not exactly the same as the Maxwell-Faraday law (MFL). MFL is more general and needs more math and more explanation and would clutter up a discussion of electromagnetic induction (EMI). But, if the demerged article only discusses FLI, then I lean toward GliderMaven’s opinion that there is no benefit to separating it out from the article on EMI.Constant314 (talk) 17:37, 8 March 2014 (UTC)

My suggestion is that the Faraday's law of induction article should, as it does now, cover both FLI and the Maxwell-Faraday equation, both in detail. The distinction is not that clear cut. If you look at the Maxwell's equations you will see that the MFE is also called "Faraday's law of induction". Feynman also refers to the MFE as "Faraday's law" so the two belong together.

As I have said before, I suggest that MLI/MFE is summarised in this article for the layman. Martin Hogbin (talk) 18:21, 8 March 2014 (UTC)

I find in Wikipedia editors should try very, very hard to completely ignore the names for things when working out where stuff goes.

As an example your argument "you will see that the MFE is also called "Faraday's law of induction". Feynman also refers to the MFE as "Faraday's law" so the two belong together." is not correct in Wikipedia.

In Wikipedia the fact that the same name is used for two different things tends to push them into different article's, not the same article, and then it would be necessary to disambiguate them.

No, what matters here in Wikipedia is how they are related conceptually. Conceptually they're deeply and intimately related, as is electromagnetic induction in general.

Things that are very highly related conceptually are covered in one article in encyclopedias/Wikipedia, and that overrides naming.

I appreciate and empathise with the point that we could write an introduction article like in a textbook, but actually Wikipedia isn't a textbook, and doing that would cause practical problems with maintaining the articles. In Wikipedia writing everything once, in one place is much preferred. Here, any introductory-type articles are specifically named as such, but 'electromagnetic induction' is not such an article.GliderMaven (talk) 01:16, 9 March 2014 (UTC)

Feynman does call the differential form of MFE as simply Faraday’s law. It’s hard to argue with that. If there is going to be that separate article, then I think the other article ought to be called Maxwell-Faraday Equation with Maxwell-Faraday’s Law and Faraday’s Law redirected there. It should start off with MFE and be mainly about MFE but also include FLI as an extensive section that has a link to EMI. Faraday’s Law of Induction should be redirect to the FLI section of the MFE article. The EMI article should also have a link to the FLI section of MFE. All my opinion.Constant314 (talk) 16:22, 9 March 2014 (UTC)

GliderMaven, I do understand your point about writing everything once only, it is a good principle for organising technical information but it is a lost cause in WP. Having the same information is several places is very common in WP and there is little that anyone can do about that. As it happens maintenance is not going to be that much of a problem as classical EM is not likely to change much.

WP is intended mainly for the general reader so there is a good reason to have a non-technical description of the concept here. 18:03, 9 March 2014 (UTC)

Constant, I do not think that there are any right answers as to the correct names for equations and laws of physics. It is all a matter of deciding how to properly give credit to the scientists involved. There is no doubt that Faraday did not propose his law in the form of what we have called the MFE. I do not think it was even Maxwell who first put it in the well known vector calculus form but Oliver Heaviside. Nevertheless, Feynman saw fit to credit Faraday for what is also usually considered one of Maxwell's equations.

One thing I think we can all agree on is that we do not want more than two articles on the subject (not counting redirects). I think we also all agree that FLI and MFE in all their mathematical forms belong in one article. My preference is to follow Feynman and call that article after Faraday in some way but I have no objection to redirects from other names that users may search under. Can I suggest though that we leave the naming of the new article until the dust has settled on the the demerge. Martin Hogbin (talk) 18:03, 9 March 2014 (UTC)

You yourself are being completely inconsistent here, doesn't MFE "deserve" its own article? I mean it was invented by a different person, and has its own history. It's a generalisation, correct in all cases, whereas the original equation isn't. Abd it is 'one of the most important laws of Electromagnetism.' By your own logic 'I think it should have its own article.' Not that I expect any consistency from you at this point.

Splitting MFE off is actually a defensible position, and one I considered before merging, and constant34 thought that's what you were going to do and seems to have thought it to be a reasonable idea. So no, we do not 'all agree' that.GliderMaven (talk) 05:58, 10 March 2014 (UTC)

You say: I do understand your point about writing everything once only, it is a good principle for organising technical information but it is a lost cause in WP. Having the same information is several places is very common in WP and there is little that anyone can do about that.

Seriously? I completely deny your argument that we should copy more because other people sometimes copy things. This only strengthens my primary point; you have done a copy fork of the electromagnetic induction/faraday law article. That's exactly where your logic leads. While a limited amount of material is sometimes copied in Wikipedia, that is never supposed to happen at the article level. :( GliderMaven (talk) 05:58, 10 March 2014 (UTC)

I like the status quo right now, one article on EMI, one on both FLI and MFE (with title "Faraday's law of induction"). You can be an expert on FLI and MFE without knowing much about lamination techniques etc., and you can be an expert at understanding EMI without being able to prove the mathematical relationship between FLI and MFE etc. But I don't think you can be an expert on either FLI or MFE without being an expert in both independently. So they should be together.

My only complaint was a lack of prominent links at the top between the two articles, so that readers may immediately understand their scope and relationship. I just tried to fix that. --Steve (talk) 14:16, 10 March 2014 (UTC)

Electromagnetism in vehicles

There is an issue with electromagnetism appearing in vehicles lately. I've seen a couple on the road. I can find out the inventions origins through the principles of science 1.)ev with two sounds of two motors 2.) if you hav a voltage reader on your ev that has two different voltage settings. 3.) if you primary use dc instead of ac induction on top of that, if the oscilation on a voltmeter goes off in midair on your electric vehicle, esp if on the grid. However, they remain illusive, they are not copyrighted for corporations but for individual inventors pursueing copyright ie troy reed.

if there is a problem with your electromagnetic vehicle let me know. The sound that comes from the electric motor should sound like a missile. If it does not, it is a standard electric car. If the battery drains completly, its another indication of it being stanard. If the wall charge is more than half-an-hour.

State of things

As of now, I feel this article is too focused on the math, and not enough on the physics. I tried some rearrangement of the intro to FL section, but as of now, it's still marred with details about path/surface integrals, sign conventions, and is generally too focused on the details of vector algebra.

It's not that vector algebra doesn't have it's place in this article, it's that the forest is obscured by the trees. This article should, IMO, cover very generally the following areas

• A) What is induction, with some history Y
• B) How does induction work Y
  • B1) Simple mathematical formulation (Faraday's Law) Y
  • B2) Illustrations showing what the magnetic flux is Y
  • B3) Illustrated examples showing you can create an EMF by varying  Partly done (illustrations missing, but these ways are at least mentionned now)
    • B3.1) The B field in a fixed geometry (e.g. field generated by an AC current)
    • B3.2) The size of the loop (e.g. shrinking the loop)
    • B3.3) The orientation of the surface (e.g. spinning a loop in a fixed B field)
  • B4) Link with Maxwell-Faraday equation, integral form only. Y
• C) Applications
  • C1) Generators Y
  • C2) Motors N
  • C3) Transformers Y
  • C4) Magnetic clamps / AC ammeters Y
  • C5) Others?
• D) Practical considerations
  • D1) Eddies Y
  • D2) Parasitic induction Y
  • D3) Others?
• E) See also

While the Faraday's law article should cover

• A) What is Faraday's law
• B) How was it discovered
• C) Mathematical formulation
  • C1) Basic Faraday's Law, with illustrated concepts for mag flux through a surface
  • C2) Link with Maxwell-Faraday equation with formal proof through Stokes theorem, including both differential and integral forms
• D) Link with Lorentz force, with formal proof
• E) 'Counterexamples' [really don't like this name]
• F) Link with relativity, tensor / einstein notation form of MFE

Headbomb {talk / contribs / physics / books} 15:27, 10 March 2014 (UTC)

That looks good to me. I think the reduction in maths and the increase in more practical explanations and examples is just what is needed. Martin Hogbin (talk) 15:40, 10 March 2014 (UTC)

Are you suggesting separate articles for Faraday's law and the MFE? I would not support that. As I say above the MFE is often referred to as Faraday's law. Martin Hogbin (talk) 17:47, 10 March 2014 (UTC)

No, I'm suggesting what we have here, one article for EM induction, and one article for FL + MFE. Not sure where you get the idea I'm suggesting splitting FL into two difference articles. Headbomb {talk / contribs / physics / books} 21:43, 10 March 2014 (UTC)

That is fine then. Martin Hogbin (talk) 22:06, 10 March 2014 (UTC)

The problem I have with all that is that, in actual reality, the articles end up practically the same. But you have to try to explain to the reader what the heck is going on. That bit is really hard.

At the top of each article you're supposed to state what the article covers. Good luck trying to explain to anyone in a sentence what each of those articles cover. If I've understood you correctly it's roughly:

1. "electromagnetic induction" This article covers induction, but not so much Faraday's law, except we do cover it, nor does it cover electromagnetism even though that's a form of induction too

2. "Faraday's law" This article covers induction and Faraday's law, but not the Faraday's law used in Maxwell's equation, oh but we do cover relativity (n.b. relativity theory usually uses the MFE equation, but we don't cover that)

3. "Maxwell-Faraday equation" This article covers induction and Faraday's law, but only in Maxwell's equation, and not relativity

That's a right dogs dinner. They are absolutely all, every one of them, about both electromagnetic induction and Faraday's law. That's a 3-way CFORK and it's quite difficult to explain to the reader what's really going on. And it causes problems. For example under electromagnetic induction you wouldn't be covering MFE, but MFE is actually the equation that is actually mostly used to design equipment using electromagnetic induction! And the Faraday's law article not covering MFE(!) is pretty bizarre too.

And this is all wrong-headed anyway. We're not supposed to be a textbook that introduces material at different levels of approximation. Wikipedia is a reference work. You're supposed to look things up in it, not read it cover-cover as a learning tool. Although we shouldn't go out of our way to make things harder, the fact that there's some tricky maths in electromagnetism comes under the topic of "tough shit". Diluting the topic down into three different articles doesn't actually make anything in any way simpler, it just hides it. Hiding information is not a legitimate goal in Wikipedia.GliderMaven (talk) 17:03, 10 March 2014 (UTC)

Yes, I missed what seems to be a splitting of the Faraday's law of induction article. I do not favour that. Martin Hogbin (talk) 17:48, 10 March 2014 (UTC)

As you will see above, Headbomb has made clear, there is no proposal to split off MFE from FLI. Martin Hogbin (talk) 22:06, 10 March 2014 (UTC)

Well OK, his explanation of what he wanted was ambiguous. What does 'link' mean, is it a wiki link?

But you've still missed the point; Breaking an article into two (or more articles) doesn't make the material simpler; it makes it harder. Simply hreaking material up onto different articles never makes it simpler. Reorganising it, yeah. If you can come up with a completely different way to present it, that can. But you're not proposing to do that.

But that aside, I'm not in any way impressed with your ever growing list of misrepresentations and mistakes; two people have indeed proposed it, including myself; and if I've understood his position correctly, constant314 only supported the demerge, on the understanding that you were going to create an article on Maxwell-Faraday equation which you are not in fact doing.

This is continuing to be a total disaster. Not only can the history not be split between the two articles, but there's no way to put the rest of the material into any sensible order either. The n dphi/dt equation has to be in all places, as does the Maxwell-faraday equation. You might be able to miss out an equation or two in one or other article, but all the other equations, most of the equations, have to be in both places. Additionally, how are you going to handle things like inductance, and transformers? Faraday built a transformer as his experimental apparatus to come up with Faraday's law. They really need to be subarticled from both places as well. Feynman specifically treats generators at the same time as Faraday's law. The list of things that are the same is far, far bigger than the list of things that are different. By the time you can write a FA quality article on each a topic, the articles are inevitably going to be 95% the same, or you've missed something important out.

And it's not like I'm on my own in treating this stuff in a single place. The Feynman lectures on Physics treat it all in a single lecture. You guys are the ones desperately trying to break it up, not me. There is no reason to do this, and doing so has only negative consequences in readability, comprehensibility, scope, and in terms of Wikipedia being a usable reference work.

I can certainly see what you're trying to do, why you're trying to do it, and what you're trying to gain; it's a superficially attractive idea, it's just that it doesn't work well in practice, and this isn't the way that textbooks and Feynman treat it either.GliderMaven (talk) 19:05, 11 March 2014 (UTC)

Demerge isn't working

The statistics say everyone is simply now having to read two articles instead of one:

Faraday's law (now peaks at 1800 hits)

Electromagnetic induction (virtually the same, now peaks at 2100 hits)

But of course the article is over 50% the same, because they really are the same topic, that you've arbitrarily split up. So you're just forcing them to read most of it twice, or at least check to try to see what the difference is; except they find that there isn't any material difference.

In effect, because of the duplication the same article is now 50% longer, and readers are having to pick their way through your mess.

I would say you've been very stupid, but that's against the rules, so I won't.GliderMaven (talk) 18:34, 6 April 2014 (UTC)

Who are you addressing here? I'm not convinced your conclusions from the data are valid. A couple of problems with the data you present: first, you are linking to "last 90 days" which is not stable, it will change every day, so in a few days time the page will be completely different from the figures you quote. Second, I do not recognise the peak figures you quote, they are not in the data. Perhaps you have assessed some kind of average by eye? There is also an enormous unexplained peak on 3rd April in the EMI data which should probably be excluded as an outlier. A better way of looking at this is with daily or monthly averages and since there can be strong seasonal fluctuations in Wikipedia use, we should compare year on year figures. Electromagnetic induction has 82750 pageviews for March 2013, that is, before the demerge. Electromagnetic induction has 58136 pageviews for March 2014. Faraday's law of induction has 33359 pageviews for March 2014. The two pages together have 91495 pageviews. That is only 10.6% higher than the 2013 figure, easily accountable by the steady increase in Wikipedia traffic or random fluctuations [2]. It's probably too soon to draw any firm conclusions, but so far the stats seem to be showing just the opposite of what you claim. SpinningSpark 11:16, 7 April 2014 (UTC)

Rubbish- ignoring the outliers, and the hits to what was a redirect page, the total number of article page hits has almost exactly doubled since the demerge.

The only reasonable explanation for this is that almost everyone is having to read or at least load both pages; pages that are more than 50% the same.

This should be entirely obvious to anyone that isn't sticking their head in the sand; and yes, I'm looking at you Spinningspark.GliderMaven (talk) 14:27, 7 April 2014 (UTC)

Note that historically the two articles were different, last year this article was practically empty; the result of these unwise edits that have been made is to copy a whole bunch of material. The total number of hits to the material that has been duplicated has doubled; everyone is hitting both pages.

This is also what happened when the articles merged, the total number of hits to electromagnetic induction did NOT go up much at all.

There's really strong evidence here that the readers want to know about both electromagnetic induction/Faraday's law, but it's been badly split over two pages.

This was never going to work, and it hasn't. The readers were happier with one article, they're only clicking across because they need to know both- there's really only one topic here.GliderMaven (talk) 14:39, 7 April 2014 (UTC)

There was a fairly clear consensus for two articles. Martin Hogbin (talk) 22:02, 8 April 2014 (UTC)

Whether it was a majority or a consensus, it hasn't worked.GliderMaven (talk) 22:36, 8 April 2014 (UTC)

I did support the demerge initially, but then it began to look like it wasn’t going to be what I thought it was going to be. I worked myself over to a mild oppose, but kept quiet because I thought Martin should get a chance to try the demerge. But as it is now there is a lot of duplication. I can see a situation in the future where an editor fixes something here but doesn’t know that it needs to fixed over there or he does know but there is a difficult editor over there who won’t let him make the same change there. So after negotiating the change over there he comes back here to make the same change here that he made there and runs into some other difficult person here and cannot get the same change here and so the two articles diverge where they should not. Upshot, now that I see how it has turned out, if GliderMaven wants to propose a remerge, I would support that.Constant314 (talk) 22:50, 8 April 2014 (UTC)

All the evidence is that the demerger has failed, I propose to remerge.GliderMaven (talk) 19:56, 2 June 2014 (UTC)

Support. I just looked at them side-by-side. I would say that they are about 70% the same with one having applications and the other having counter examples and relativity. While I see a distinction between Faraday's Law of Induction and the Maxwell-Faraday equation, I do not see a difference between Faraday's Law of Induction and electromagnetic induction.Constant314 (talk) 00:57, 3 June 2014 (UTC)

Oppose Most people seemed to think that they were two different subjects. Maybe we should just remove some of the overlap. Martin Hogbin (talk) 13:18, 3 June 2014 (UTC)

But you already overlapped them as little as possible. Whatever your thought, being 70% the same, and everyone having to read both says they are de facto the same subject.GliderMaven (talk) 20:46, 3 June 2014 (UTC)

What I would like to see happen is this. Move the applications to Faraday's Law of Induction. Move the Maxwell-Faraday Equation stuff and maybe the relativity stuff to this article, then remove everything else from this article and then rename it as Maxwell-Faraday Equation. Then set up Electromagnetic Induction to redirect to FLI.Constant314 (talk) 21:25, 3 June 2014 (UTC)

The current two articles are how the subject was treated in WP for some time, before they were merged without consensus. Any changes from this should have clear community consensus before any action is taken. Martin Hogbin (talk) 21:48, 3 June 2014 (UTC)

No, the only article here was a stub, as you well know. Merging a stub with an article which it has massive overlap with is perfectly proper. Your ideas are bad, they have not worked, and you no longer have consensus.GliderMaven (talk) 23:52, 3 June 2014 (UTC)

Agree, there should be a consensus. Constant314 (talk) 23:39, 3 June 2014 (UTC)

Oppose I agree that if there is overlap, then we need to figure out how to split the material. When the merge was proposed over a year ago, I opposed it but offered an idea on which information to transfer from the Faraday's Law article to here to destubify this article. I would like to see what happens if we start from there. I apologize that I haven't been able to dig into this like I had wanted but RL issues arose that took priority for me. There will be some overlap, but we can minimize it but realizing that there is a difference between the phenomenon and the law or tools that we use to describe that phenomenon (like Coulomb's law and electrostatic induction). The history sections could be a good example of this. Very rarely does the discovery of a phenomenon coincide with the actual formulation of the law. EM induction was probably first noted by Arago in 1822, Faraday's experiments were in 1831, and he didn't come up with the single law ("If a terminated wire moves so as to cut a magnetic curve, a power is called into action which tends to urge an electric current through it.") for all his results until 1832. But getting from that statement to the mathematical, quantitative formulation that most modern texts refer to as Faraday's Law took several years and several missteps. Most of those missteps were in first mathematical theories of induction that, instead of starting on Faraday's views, tried to construct very complex mathematical theories, usually involving odd potentials, akin to Ampere's to explain the Faraday's observations. The first mathematical formulation that we might recognize doesn't appear until 1845 with Franz Neumann, and we don't get Maxwell's more mathematically precise statement of the law until 1854, and so forth in the history of the law. To sum up, IMO there is ample room to distinguish the history sections of the two articles (a good resource would be Darrigol's "Electrodynamics from Ampere to Einstein"). I think the same could be said of other sections that might have overlap.

On whether we split the articles further to make a distinction between Faraday's Law and Maxwell-Faraday Equation, I would be more comfortable if we had some reliable sources that explained and agreed on the distinction. Otherwise I fear would be creating and a neologism that is not verifiable nor deserving of that weight. --FyzixFighter (talk) 04:34, 4 June 2014 (UTC)

Thanks for starting a reasoned argument on how best to present this subject. I do not insist that everything must remain that it is, only that things are only changed if there is a clear consensus do do so. I will start a section below for discussion of this subject. Martin Hogbin (talk) 09:07, 4 June 2014 (UTC)

Hear, hear to that. The comparison with Coulomb's law/electrostatic induction is particulary relevant. If FyzixFighter could add something on history, about which they seem quite knowledgeable, that would be wonderful. Here are some sources that discuss Faraday's and Maxwell-Faraday's law [3][4][5]. The last of these makes an argument that the two laws cannot be quite treated equivalently and Faraday's is the more general. Here is a source giving some of the history [6]. SpinningSpark 11:19, 4 June 2014 (UTC)

I'll take a stab at the history/discovery sections over the next couple of evenings if I can. Certainly over the weekend I should have time to make an attempt. Darrigol is the one that's really quite knowledgeable on the subject, so it might be a bit heavy on the cites to his book to start out with. --FyzixFighter (talk) 12:31, 4 June 2014 (UTC)

I don't have any problem with improving the historical section, but how is any of this going to help with the Faraday's law part which, practically, must be in this article and, it has now been repeatedly shown, cannot be practically summarised down?GliderMaven (talk) 15:11, 4 June 2014 (UTC)

With all due respect, I don't find that Coulomb's law/electrostatic induction is at all relevant. They're are related, but significantly different topics with hardly any overlap; whereas electromagnetic induction and Faraday's law have about 70% overlap.GliderMaven (talk) 15:11, 4 June 2014 (UTC)

Being enthusiastic about adding material is good, but it's not solving the problem.GliderMaven (talk) 15:11, 4 June 2014 (UTC)

Oppose. Coming late to the party, the scope of these articles seems to be separating nicely. The demerge seems to be getting along fine. I think it needs to be given more time, say six to twelve months, before it is worth reviewing it again. — Cheers, Steelpillow (Talk) 22:01, 5 June 2014 (UTC)

How to present this subject in WP

There is some disagreement on exactly how the subject of electromagnetic induction should be presented in WP, in particular as to whether is should be in one article or more than one and, in all cases what the articles should be called. Martin Hogbin (talk) 09:07, 4 June 2014 (UTC)

I think User:Headbomb's outline above in Talk:Electromagnetic induction#State of things is the way to go. Faraday's Law, as original stated by him in 1832, covered both the flux-changing and motional emfs. I don't have Griffith's in front of me, but I think it makes a similar case to [7] that what we have been calling the MFE is a subset of the original Faraday's Law. So the Faraday's Law article should probably have a section on this nuanced subset/distinction. --FyzixFighter (talk) 12:40, 4 June 2014 (UTC)

Yes, I supported that at the time and I still do. We must remember though that it is not our job to decide what is Faraday's law and what is not, based on our OR; we should use the terminology and nomenclature supported by most current reliable secondary/tertiary sources. Martin Hogbin (talk) 18:52, 4 June 2014 (UTC)

Neither is a subset of the other, they make different predictions.GliderMaven (talk) 11:27, 5 June 2014 (UTC)

But that is quite a distinct question from where it should be described; Wikipedia does not cover a single narrow thing on each page. There's nothing even stopping an article covering diametric opposites for example yes and no.GliderMaven (talk) 11:27, 5 June 2014 (UTC)

It is wrong and bad to divide things up too much. As I pointed out above, Headbomb's suggestion does not follow the way Feynman treats this, Feynman treats it all in one article/lecture/chapter.GliderMaven (talk) 11:27, 5 June 2014 (UTC)

@Martin: I agree completely and apologize if I seemed otherwise - we really need to follow the secondary/tertiary sources closely to make sure we're not engaging on OR or inventing our own neologisms to justify perhaps our own unique take on the subject. One of the challenges will be that there isn't exactly a uniformity in what is called "Faraday's Law". Maybe I'm wrong, but that's what it seems like to me. There are a few sources that address that non-uniformity, for example Griffith, "Introduction to Electrodynamics", pp 302-303 which uses "universal flux rule" for the law that covers Faraday's three experiments but tries to reserve "Faraday's law" for electric fields induced by changing magnetic fields, and Mansuripur, "Field, Force, Energy and Momentum in Classical Electrodynamics", pp 32-33 which says that Maxwell's third equation (curl of E) is usually what's meant when referring to Faraday's Law but that it is a more limited (not really covering motional emf, like Griffith notes) than Faraday's original conception of his law. I would quibble a bit with Mansuripur because Jackson in section 5.15 of his 3rd edition text was able to show that the integral form of Faraday's Law/Maxwell's 3rd equation (Mansuripur's equation 10b) can include motional emf if you properly move the total time derivative from outside the integral to inside the integral (Jackson's equation 5.137). Jackson doesn't make the distinction that Griffith does, and perhaps 5.137 is why, but now I may be getting a little to close to OR territory and I feel like I've deviated a bit too much from the more general topic at hand.

Anyways, there was never consensus for the original merge, and since I wouldn't describe there being a strong consensus either way currently, per WP:No consensus "lack of consensus commonly results in retaining the version of the article as it was prior to the proposal or bold edit" (the merge being the proposal or bold edit). If GliderMaven and others feel that the consensus building is at loggerheads, perhaps its time to explore other dispute resolution options. --FyzixFighter (talk) 13:07, 5 June 2014 (UTC)

I'm very sorry if I hurt your feelings, but you were and are wrong. Wikipedia is not an introductory textbook, it's a reference work.

Reference works always have things in a single place as much as possible. Splitting electromagnetic induction across two or more articles is a really, really terrible idea; everything ends up duplicated and/or half-assed.

And we have the hard evidence for this, right now, everyone is having to load both pages, only to discover the same equations and basically the same description. That's because Wikipedia is a reference work, people are trying to look things up, and you're forcing them to load a second page, just in case, only to discover they've wasted their time! YOU'VE wasted their time! A thousand of people, every day! Half a million people, every year!GliderMaven (talk) 13:56, 14 July 2014 (UTC)

Scope of this article

What is the scope of this article?

I claim that the scope of this article is everything to do with electromagnetic induction, Faraday's laws, Maxwell-Faraday equation, generators, eddy currents, the history of electromagnetic induction and how electromagnetic induction and relativity interrelate. Faraday's law (in any sense) is actually formally a subset of this one. This is an encyclopedia article in an encyclopedia, and hence must cover it encyclopedically, which is to cover the topic from all sides. This is the main topic for the area. You can summarise more or less detail, but this topic is the most general, and is the main one.

Does anyone seriously disagree with that? If you do, please even try to explain how knowledge of electromagnetic induction doesn't cover it.GliderMaven (talk) 14:11, 5 June 2014 (UTC)

Makes sense to me. Coverage can be shortened on any given topic if there is a main article to link to, but it needs to be present here. — Cheers, Steelpillow (Talk) 21:44, 5 June 2014 (UTC)

I though the general view was that this article should cover everything to to with EMI, but in a mainly non-technical way, suitable for the general reader. If all the aspects you name above can be treated in a way that is not too technical for the general reader then they should all be in here. I would leave most of the maths and detailed discussion of EMI and relativity to other articles and add more in the way of practical applications here.

The maths and details should be covered in other articles. Martin Hogbin (talk) 16:33, 6 June 2014 (UTC)

Eh... "everything" is too large. Or could be too large. Not quite sure how large is your everything, but there's a lot of things related to EM induction that fall outside of the scope of the article, IMO, so we need to use restraints about dropping the less-relevant stuff (e.g. advanced inductor design, e.g.). You're quite right about Faraday's law being a subtopic of EM induction, but it's a subtopic so large that it needs to summarized here (EMI article), and detailed there (FL article). We also need to greatly simplify and visually illustrate the current summary of FL in this article, because it's way too obscure for anyone but people who already know what FL is. I've outlined what the scope of the article should be above, now it's just a matter of actually making edits so the article falls in line with the outline. Headbomb {talk / contribs / physics / books} 05:00, 24 July 2014 (UTC)

Gave the article a good trim. There should now be much less math, and a much stronger focus on the phenomena, and we now should be able to see the forest. Headbomb {talk / contribs / physics / books} 19:41, 19 May 2016 (UTC)

Grammar

The phrase "many kinds of device" is currently used in this article. The grammar of this phrase is that the kinds are many and are therefore plural, while the notion of a device is not "many" and is therefore singular. Therefore it is ungrammatical to write "many kinds of devices". — Cheers, Steelpillow (Talk) 08:36, 15 August 2014 (UTC)

Given the context of the sentence, the author's intent is that more than one device makes use of this technology; therefore, the correct word here is "devices." The key clue to this understanding is the modifier "have," rather than "has" in the verb "been invented." "Have been invented" is the plural form of the verb "been used." Had the author typed "has been invented," then the correct word would have been "device." Aasarsak (talk) 21:01, 20 March 2015 (UTC)

No. It is the many kinds of device that have been invented. A single kind replicated would not be plural in this context. — Cheers, Steelpillow (Talk) 21:05, 20 March 2015 (UTC)

The noun being acted upon by the verb in this sentence is "device." The verb conjugation is plural; therefore, the noun which it modifies must also be plural - hence, it should be "devices." Aasarsak (talk) 03:40, 21 March 2015 (UTC)

I believe that in the sentence in question, device is the object of the preposition of. I would go with device singular.Constant314 (talk) 03:50, 21 March 2015 (UTC)

Flux cutting the conductor

Assuming for the moment that flux cutting the conductor caused the induced EMF then the EMF would be proportional to the rate of flux cutting and not the time derivative of the flux cutting. But really, ${\Phi _{\mathrm {B} }}$, in the equation ${\mathcal {E}}=-{{d\Phi _{\mathrm {B} }} \over dt}\$, is the surface integral of the flux density over the closed loop (lets just talk about a single loop for now).Constant314 (talk) 21:20, 2 December 2014 (UTC)

The comment “One could create a magnetic field in a tight circle inside a conducting loop that did not intersect the conductor at all. That would not induce any emf.” Is incorrect. There would be an induced EMF. You can make the flux cutting model work, but it is highly contrived. The modern explanation is the EMF arises from the time derivative of the magnetic vector potential. The idea of the field moving is now depreciated. The modern view is the field changes strength and direction in a way that looks like motion but actually there is no motion, there is only a propagation of the field value rather than the field itself. Moving lines of flux is a useful artifice for visualization but it has theoretical problems that I don’t remember for sure but I think the problem with moving lines is that you cannot make superposition work for them.Constant314 (talk) 21:44, 2 December 2014 (UTC)

I'll defer to you on that, but I am having trouble believing that a mile wide loop of copper will have anything induced in it from, say, a small diameter iron core in the centre of the loop with all the magnetic flux concentrated in that core. There can be no $\nabla \times \mathbf {E} =-{\frac {\partial \mathbf {B} }{\partial t}}$ at the conductor since there is no B field at the conductor. Perhaps someone should do the experiment. SpinningSpark 01:17, 3 December 2014 (UTC)

This is an application of Aharonov–Bohm effect which shows that the magnetic field has effects even where B is arbitrarily close to zero. The principal actor is the vector potential. Visualize your big coil being driven. You would not have any trouble believing that the little coil picked up some EMF. But the mutual inductance is the same regardless of which coil is driven so if you drive the little coil with same current that you drove the big coil then the big coil will pick up the same EMF that the little coil picked up when the big coil was driven.Constant314 (talk) 02:16, 3 December 2014 (UTC)

Aharonov–Bohm huh? Never too old to learn something new. SpinningSpark 02:29, 3 December 2014 (UTC)

Aharonov–Bohm is a QM effect, and has nothing to do with electromagnetic induction.

It has to do with the fact that the magnetic field can have significant effects even when B (but not A) is arbitrarily close to zero. Build an ideal toroidal transformer with total B field confinement by the primary. Wrap the secondary around the primary with a 1:1 turns ratio but make the diameter of the secondary 20% bigger than the primary so that there is a nice indisputable gap between the primary and the secondary. The primary is carefully wound for total B field confinement. The B field in the gap is zero. The B field in the vicinity of the secondary is zero. But it still functions as a perfectly ordinary transformer.Constant314 (talk) 06:20, 3 December 2014 (UTC)

Congratulations on continuing not knowing what the Aharonov–Bohm effect is. It's just a change in a diffraction pattern, it's got nothing to do with electromagnetic induction.GliderMaven (talk) 11:31, 3 December 2014 (UTC)

A small coil inside a very much bigger one has virtually no mutual inductance, when you integrate the field over the area of the bigger coil, you get very close to zero net flux. The normal component of the flux has a sign, and very nearly as much flux goes into the surface as comes out of it- it cancels almost completely. Only the flux that goes through the small coil, loops around the wire of the big coil and back into small coil gives a non zero result, and virtually no flux does this.GliderMaven (talk) 05:06, 3 December 2014 (UTC)

But some flux from the small coil does link the big coil and mutual from the little coil to the big coil is the same as the mutual from the big coil to the little coil. Let’s say you drive 1 Amp at 1 MHz in the big coil and measure an EMF of 1 mV in the small coil. Then you drive the small coil with 1 amp at 1MHz and measure the EMF on the big coil and it is 1mV. But before we get carried away, look at the first two sentences and see if you agree.Constant314 (talk) 06:20, 3 December 2014 (UTC)

You'd get more like femtovolts on the small coil, but yes the incredibly tiny coupling coefficient is the same in each direction.GliderMaven (talk) 11:31, 3 December 2014 (UTC)

The comment “One could create a magnetic field in a tight circle inside a conducting loop that did not intersect the conductor at all. That would not induce any emf” is indeed correct. We can approximate such a situation by running a wire along the axis of the loop and passing a current through it. Provided the wire is accurately aligned, no emf will arise - this is actually a very good way of aligning the loop accurately around a fixed wire. The inverse situation, where a current passes in a coil, allows lamination of an iron transformer core to dramatically reduce induced emfs in the laminations, because emfs are not induced in the plane of each lamination, but only across their thickness. Transformer action, aka inductive coupling, only occurs where two conductors are not orthogonal.

One commonly talks of "flux cutting the conductor" only when dealing with mechanically dynamic situations such as motors and dynamos. Faraday's law applies in both mechanically static situations, where the flux magnitude is changing, and in mechanically dynamic situations, where the conductor is passing across a fixed magnetic field. The explanation - along with any theoretical approach - needs to be couched in general terms which embrace both situations, i.e. whether or not the flux is cutting across any conductor.

It is very easy to get confused in theoretical matters if we do not constantly test our ideas against such basics of practical electromagnetics. WP:LEGS beautifully illustrates the logical pitfalls. — Cheers, Steelpillow (Talk) 11:42, 3 December 2014 (UTC)

I see you changed it back to “rate of change of the magnetic flux through the circuit”. My real issue here is just exactly what does the word through mean in this context. It could mean: 1. the total magnetic flux going through the surface which is bounded by the path of the circuit or 2. The flux cutting through the path of the conductor. The first meaning is correct and the second is incorrect. I propose to change the text to “rate of change of the magnetic flux encircled by the circuit”. But please let me know if you think ${\Phi _{\mathrm {B} }}$ means anything other than a surface integral of the flux density.Constant314 (talk) 17:03, 3 December 2014 (UTC)

I am not sure what you mean. Your 2. seems to be saying that the flux is lying in wait, passively cutting across or through the future path of the conductor - this is not at all what one understands by "through the circuit" in this context. The path of a moving conductor is not an electrical circuit. If the conductor is moving and cutting a constant flux, then the rate of cutting is just the rate of change across the circuit. BTW, I just changed "through" to "across" because "through" a circuit usually means along its constituent conductors, but other than that I can see no problem with the old wording. — Cheers, Steelpillow (Talk) 18:33, 3 December 2014 (UTC)

I agree that through a circuit is ambiguous, but across a circuit is even more so. ${\Phi _{\mathrm {B} }}$ is the total flux through a surface bounded by the circuit and that is what the article should say.Constant314 (talk) 18:48, 3 December 2014 (UTC)

Over at Faraday's law of induction we find, "The induced electromotive force in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit." So, OK I'll revert "across". But if you want to introduce non-standard verbiage about surface integrals and stuff, I suggest you take it up at Talk:Faraday's law of induction - this is the wrong place. — Cheers, Steelpillow (Talk) 19:31, 3 December 2014 (UTC)

There is nothing non-standard about surface integrals. The use of the surface integral of B to mathematically define Faraday’s Law is found in all the following:

Feynman, Lectures on Physics, Vol 2, page 17-2.

Purcell, Electricity and Magnetism, 1965, p242.

Jackson, Classical Electrodynamics, 3rd ed, p 209.

Jordan and Balmain, Electromagnetic Waves and Radiating System, 1968 p79 and p100.

Harrington, Introduction to Electromagnetic Engineering, Dover 2003, p49.

Harington, Time-Harmonic Electromagnetic Fields, McGraw-Hill, reissued 1987, p4.

Hayt, Engineering Electromagnetics, 5th ed,, p313 I particularly like Hayt's description "The magnetic flux is the flux which passes through any and every surface whose perimeter is the closed path.

Is it so onerous to say the flux passes through the surface bounded by the circuit. Its only the four extra words that are Italicized.

It's no good hammering on about it here, like I said, take it to the topic article's talk page. — Cheers, Steelpillow (Talk) 22:26, 3 December 2014 (UTC)

That is an unhelpful position to take. If there is a problem with the text in this article it can quite properly be discussed here regardless of what is written in any other Wikipedia article. SpinningSpark 02:26, 4 December 2014 (UTC)

Technically. But I think you will find my suggested approach more helpful in the long run. — Cheers, Steelpillow (Talk) 09:01, 4 December 2014 (UTC)

It is highly confusing when a discussion involves more than one talk page. Once we agree here we can make the same change there. Also, I would point out that wikipedia itself is not considered a reliable second source, so even if another article says something different, it does not matter for this discussion about this article.Constant314 (talk) 14:42, 4 December 2014 (UTC)

Flux cutting the conductor restart

In the Faraday's law and the Maxwell–Faraday equation section

The text was “ is equal to the rate of change of the magnetic flux through the circuit.”

I am changing that to “is equal to the rate of change of the magnetic flux enclosed by the circuit.”

I have provided two in-line citations with virtually the same wording (the sources say path instead of circuit).

The reason for this change is there are two interpretations of flux through the circuit

• The correct one which is the flux through a surface bounded by the circuit.

• The incorrect one meaning lines of flux pushed through the conductors, which is not consistent which the equations.

If anyone doubts this look at the equations that follow that text.

${\mathcal {E}}=-{{d\Phi _{\mathrm {B} }} \over dt}\$,

which says that the emf is equal to the time rate of change of The Flux.

and

$\Phi _{\mathrm {B} }=\iint \limits _{\Sigma (t)}\mathbf {B} (\mathbf {r} ,t)\cdot d\mathbf {A} \ ,$

which says that The Flux is the integral of the B flux density over a 2 dimensional surface bounded by the closed path, $\Sigma$, which is the path of the circuit.Constant314 (talk) 03:38, 5 December 2014 (UTC)

References

To me "through", "across" and "enclosed by" all mean the same thing in the present context. If you beg to differ, I care not a whit which of the three is used, so I have no issue with the meat of your edit. I have however corrected your formatting per Wikipedia practice. — Cheers, Steelpillow (Talk) 12:13, 5 December 2014 (UTC)

I appreciate that.Constant314 (talk) 18:08, 5 December 2014 (UTC)

Also

Either the sources support prior discovery by Faraday or they support independent discovery by him and Henry. Whichever they support, the article needs to tell a consistent story and not try to have it both ways. It is not customary to dicker over who thought what when. Is there a problem with that? — Cheers, Steelpillow (Talk) 19:54, 26 February 2015 (UTC)

I see that SQMeaner (talk · contribs) has attempted the same ungrammatical edit at Transformer, having first invited me in this edit comment to discuss it here, but then failed to respond when I did so. — Cheers, Steelpillow (Talk) 10:01, 16 March 2015 (UTC)

How is it ungrammatical to add 'also' to the sentence? The way the sentence is laid out now it could be interpreted to mean Michael Faraday is credited with the discovery of mutual induction because he was the first to publish and not because he was the first to make the discovery. I was just trying to make it clear. SQMeaner (talk)

For any reader capable of counting dates, the current sentences, "Electromagnetic induction was discovered independently by Michael Faraday in 1831 and Joseph Henry in 1832" and "In Faraday's first experimental demonstration (August 29, 18311)" leave no doubt as to who was first. I take your point about the ambiguity as to why he is credited, but the "also" is meaningless without the explanation that you give here. [rewritten because I misread your reply above] — Cheers, Steelpillow (Talk) 11:05, 17 March 2015 (UTC)

Weberian Approach

According to the linked Weber electrodynamics article, "[t]he theory is widely rejected and ignored by contemporary physicists, and is not even mentioned in mainstream textbooks". So what is the justification for including it in our article? Especially without any critique. SpinningSpark 09:31, 19 April 2015 (UTC)

I have demoted it to See Also. — Cheers, Steelpillow (Talk) 11:21, 19 April 2015 (UTC)

I do not think it belongs in the article even as an Also link.Constant314 (talk) 14:12, 19 April 2015 (UTC)

Fair enough. I think its historical interest deserves a See Also link somewhere, so I have moved it to Classical electromagnetism because Electrodynamics redirects there. — Cheers, Steelpillow (Talk) 14:46, 19 April 2015 (UTC)

flux linkage in a multi-layer coil

If a multi-layered coil is wound around a ferromagnetic core, is the flux linked with the wire in the innermost layer the same as the flux linked with the wire in the outermost layer? — Preceding unsigned comment added by Thecoolsundar (talk • contribs) 09:07, 28 April 2016 (UTC)

It depends what you mean by "the same flux". Provided the windings are tight and have equal turns, yes the flux accounted for in each layer will be the same amount. However for n layers, each will account for 1/n of the total flux through the core. Like cutting up a cake - different pieces but all the same size. I don't think this is worth adding to the article though. — Cheers, Steelpillow (Talk) 10:01, 28 April 2016 (UTC)

For almost all practical purposes, yes. If you are being mathematically exact, the outer layer sees a little less flux. It depends on the shape of the core and the space between the layers. Based on nothing, I would guess that the difference is on the order of parts per million. Constant314 (talk) 13:37, 28 April 2016 (UTC)

Demerge still hasn't work

There's only one topic here. Splitting the topic across two different pages doesn't work- there's absolutely no good way to do it. The number of page hits is exactly the same for both pages, that's because readers are having to hit both pages, but they get virtually the same information.

The only reason there's any differences is because editors are deliberately leaving out information to falsely create an artificial difference. To complete these articles-to reach FA quality-you will have to move all the information from this article to that one, and that article to this one. Wikipedia needs one good FA-quality article covering all of electromagnetic induction, not two sub par articles with arbitrary omissions.

For example, why is the relativity stuff only under Faraday's law? I literally have no idea, is that material not part of the physics of electromagnetic induction??? It absolutely is. Are not applications of Faraday's Law part of the Faraday Law topic??? Yes they are. We need to copy that material from here to there, and the relativity from the there to here. What about the topic scope in either article stops us doing that? Nothing, really nothing at all, because they're the same topic; and if they're the same topic, then there's only one article.

It's not like we have a 'skiing' and 'theory of skiing' articles where there's lots of complicated equations only in the theory article; everyone agrees we have to have the equations in both places; but really we have to have the relativity stuff in both places as well, and it makes no sense to not have the applications in both places either.

There's absolutely no way you could go FA with the current abortion; neither article is complete nor good; and if you can't do that, then you've fucked it up. We ought to be able to take this FA, but that's not possible under any fair review, not with this structure.GliderMaven (talk) 03:27, 20 May 2016 (UTC)

Faraday's law is clearly a sub-topic of electromagnetic induction and the present article should not be cut down just for the sake of de-duping - duplication across related articles is fine, per WP:RELART. I agree with GliderMaven there. But whether Faraday's law of induction deserves its own article is unclear to me. Certainly, the relativity discussion is more general and belongs here rather than there. There is a case for either moving much of the counterexample discussion there to the Faraday paradox article - or of merging the latter, which is far too verbose and detailed, back into Faraday's law. There is a discussion of the Lorentz force and Faraday's law of induction in the article on the Lorenz force, which also covers Maxwell-Faraday and is longer than the combined discussion in the "main article" (Faraday's law of induction) that it links to: perhaps that should be moved across to help fill the Faraday article back out, as it is too detailed a side-issue to come here. The current situation is certainly a mess - phrases like "dog's breakfast" and "rat's nest" spring to mind. I'd suggest some wider reorganization of content to create reasonably coherent, focused and complete articles before worrying about whether any need to be merged. — Cheers, Steelpillow (Talk) 10:33, 20 May 2016 (UTC)

It's not cutting down for sake of de-duping, but for sake of focusing on the phenomena (which is/should be the focus of this article) rather than the math (which is/should be the focus of Faraday's law), per the outline presented above. The 'demerge' has worked, and is working. Headbomb {talk / contribs / physics / books} 12:34, 20 May 2016 (UTC)

It was my understanding, that when this article and Faraday’s Law of Induction were demerged that this article would be a general discussion of induction and that FLI would have the math. Headbomb has made substantial progress on this article toward that goal. However, to me, the two articles are about the same thing. The split seems artificial. That being said, the last time that this was discussed, the majority wanted to keep the two articles separate. I regard that issue as settled. Regarding the article on Faraday paradoxes, that article is a mess. Please don’t merge it into either this article or FLI. Constant314 (talk) 15:19, 20 May 2016 (UTC)

I agree that the Faraday paradox mess would need sorting out before it could be merged, have no fears on that score. While I am here, I am in turn reassured that de-duping is not an issue. — Cheers, Steelpillow (Talk) 16:57, 20 May 2016 (UTC)

You are "reassured"? Why does the relativity stuff go under Faraday's law? I don't understand. Why do applications of Faraday's law go here, but not under Faraday's law? I don't understand.

It seems to me that the only reason that the articles are laid out that way is because people are revert warring according to some arbitrary, petty random rationalisations. You're supposed to say at the top of the article what the scope is, and stick to it, but that hasn't happened. Just because people are in a majority to do anything, doesn't mean what they're doing is actually making sense. You're supposed to maximally put stuff together so that people looking things up can find them easily. Instead, things are just randomly being stuffed in anywhere.GliderMaven (talk) 22:27, 20 May 2016 (UTC)

It's fairly simple, but you refuse to hear the explanation. Induction is about the phenomena, FLI is about the mathematical details. Exactly like we have an article on gravity and one on Newton's law of universal gravitation. Headbomb {talk / contribs / physics / books} 22:31, 20 May 2016 (UTC)

It's even simpler than that, this article is about the whole of electromagnetic induction, all of it, including Faraday's law, and relativity, and that other article is supposed to only be about Faraday's law. You're supposed be able to read the first few sentences and that's the scope.

You'll notice that your description of what the article is supposed to cover does not match up at all with what the article actually covers. Nor do the leads specify what you just stated.

That's because of all of: a) the articles are in general a pile of shit b) you haven't written the leads properly c) you've got absolutely no plan that can fix these problems and take the article(s) FA.GliderMaven (talk) 02:42, 21 May 2016 (UTC)

@Headbomb: You say that consensus is to separate out the maths to another article, yet you bury a passing mention of Lenz's law in a mathematical discussion of a different law and delete any qualitative commentary. Could you explain this please? — Cheers, Steelpillow (Talk) 08:44, 21 May 2016 (UTC)

Lenz's law is the implication of the sign. It's mentioned quite clearly in the section, but I just don't see why it needs it's own section. To consider it 'separate' from Faraday's law is mostly a historical thing, because Faraday didn't describe that explicitly in the early 1830s, and Lenz got there between Faraday and whoever first wrote the mathematical version of the law.

I think Lenz's contribution to the understanding of induction probably ought to be mentioned in the history section more, but once we write emf = -dΦ/dt, then that covers both the contributions of Faraday and Lenz, and I don't see a need for a separate theoretical section on Lenz' law since it's covered by that equation. I suppose one could call that the Faraday-Lenz law, but that's not what people do IRL. Headbomb {talk / contribs / physics / books} 11:53, 21 May 2016 (UTC)

Thank you. I guess my remaining concern is that there seem to be a lot of equations for a section in the "non-mathematical" fork. I know it's concise and elegant and all that, but I'd hope that anything that can be explained in text should be, and anything that does really need the mathematical formulation can be linked across. After all, if Michael Faraday didn't need the maths, we shouldn't either! — Cheers, Steelpillow (Talk) 18:59, 21 May 2016 (UTC)

Faraday also didn't convince a lot of people initially because of the lack of sound mathematical support. I think the current version strikes a good balance there however, with the definition of flux, the mentioning the concept of flux linkage, the faraday law, definition of the EMF, and the integral form of the Maxwell-Faraday equation. I think what needs more work now are the examples. Having one for each of the three ways to generate an EMF would go far, while making a clear link to which method they exploit to generate that EMF. This would also allow us to talk give examples of motional EMF and transformer EMF, terms which are currently not very well defined/explained. Headbomb {talk / contribs / physics / books} 19:11, 21 May 2016 (UTC)

Faraday's law and relativity - Feynman’s comments

I’ve been examining Feynman’s comments on the two phenomena. He says, “We know of no other place in physics where such a simple and accurate general principle requires for its real understanding an analysis in terms of two different phenomena.” I believe that his comments are being misapplied. The book is not a reference book; it is not even a text book. It is a transcript of lectures for sophomores. As a teaching device, Feynman occasionally makes intentional incorrect statements which he fixes later. I believe that this one of those cases. When you shift to the frame of reference of the moving charge, v x B disappears in the force equation but E’, the transformed E-field, has an added component of v x B, so that the force experienced by the moving charge, in its frame of reference, is given by F=qE’. In other words, the principle of force on a charge requires for its real understanding an analysis in terms of one phenomenon and special relativity. Constant314 (talk) 15:48, 21 May 2016 (UTC)

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Figure needs improvement

A simplified depiction of a Faraday's disk, showing the major components.

As drawn, the current would mainly simply travel around the circumference of the magnetic field and return to its origin instead of exiting the disk via the brush. In other words, it produces a lot of eddy current but little external current. To make it work, the magnetic field must cover the entire disk and ideally be uniform, or at least have axial symmetry. — Preceding unsigned comment added by Constant314 (talk • contribs)

Not only that, but this is likely copyrighted. Headbomb {t · c · p · b} 02:03, 1 March 2018 (UTC)

Article issues and classification

The article is tagged "unsourced statements" since August 2016. The B-class criteria #1 states; The article is suitably referenced, with inline citations. It has reliable sources, and any important or controversial material which is likely to be challenged is cited. There are unsourced sentences, paragraphs, subsections, and sections. Citations need to be provided or the article reassessed. -- Otr500 (talk) 03:00, 1 March 2023 (UTC)