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Talk:Electromagnetism: Difference between revisions

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Why no mention of the Fine-Structure Constant which is directly related to EM? I don't really understand how it can't be mentioned in the first paragraph let alone the entire article. —Preceding unsigned comment added by 216.163.247.2 (talk) 11:32, 11 May 2011 (UTC)[reply]

I'm actually kind of aggravated. I'm trying to understand the theoretical, even philosophical, nature of magnetism, polarization, etc. etc... For instance, does not magnetism have a lot to do with the concept of an object's direction of "spin", as is tends to dictate the position of the poles in a perpendicular direction? Shouldn't we have some more fundamental explanations going on here, especially in the beginning? Beginning the article with "electro" this and "electron" that, is kind of like a case of 'using the term in the definition'. I'd do it myself, obviously, if I didn't come here to understand it myself. I would propose something along the lines of:

"Electromagnetism" is a physical phenomenon resulting from an object which is said to exhibit polarity. Cases of polarity usually result from an object's spin, elementary orientation in single direction, and other such cases of binary opposition of the aspects of a single object. Electromagnetism, then, is considered to be a "force" which tends to produce effects in other nearby objects as a result of the transactions between the poles... etc. etc... I mean, what -is- electromagnetism? Calling it electrons in movement is presumptuous. —Preceding unsigned comment added by 72.242.110.218 (talk) 18:06, 15 September 2009 (UTC)[reply]

Thanks for your comment. I agree that the article needs work. I like the historical material that is already there, but we need a better introduction and overview of the theory, with emphasis on Maxwell's equations. I hope to have time to work on it myself, and hopefully other scientifically-oriented editors will be able to weigh in as well. Hickorybark (talk) 15:38, 3 January 2010 (UTC)[reply]

Next, there's how to transform the electric field under relativity, then there's defining and calculating B (an extremely long section since it turns out to be a combination of relativity and E), then how B and E transform under relativity, and finally a derivation of the wave equation for electromagnetic waves. So much to do, so little time. The vector potential is probably also worth mentioning...

Some points:

The magnetic field due to a wire is stationary only if the wire is at rest in an inertial frame and carries a stationary current. The electric field between the plates of a capacitor is stationary only if the plates are at rest in an inertial frame and have a stationary charge distribution.

The form did not work (on my computer).

I think the derivation of the wave equation should go under electromagnetic wave or under wave equation, maybe even under electromagnetic wave equation. Otherwise, this article is going to get too long. I may take a crack at deriving the WE soon, since I want to refer to it for nonlinear optics. As for the equations, I can't find a font with ∇ in it. Perhaps curl and div would be better, though this won't match the rest of the Wikipedia -- DrBob

Ok, right about the article's length. You may want to try Mozilla as a browser, and from what I've heard the special characters used in Wikipedia are an HTML standard. At any rate, the wave equation isn't that tough to derive (now that I have my notes to look at), just take the curl of the two Maxwell's equations that have the curl in them, and use the mathematical identity:

∇×∇×A = -∇²A + ∇(∇·A)

for any vector field A (there may be some caveats, but I'm fairly sure that they don't apply to actual magnetic and electric fields). Then use the fact that you want speed of light in a vacuum to say that div(E) = 0 and curl(j) = 0. It gets considerably more sticky in matter since those last two are no longer true and they're tied to particles that have mass and their own electric fields. --BlackGriffen

I just wanted to ask about the use of the permittivity of free space. I would think it is better to use the permittivity as a general variable (&epsilon) so the formulas would be valid if the charges were suspended in glass or any other medium besides free space. I wasn't sure whether there was a reason to use the free space value, so I didn't change it.

There is unnecessary comment in one part of this article which says « Carlo is gay» which i think should be removed. a little serious please

Yup. I agree

[http://de.wikipedia.org/wiki/Gr%F6%DFen_und_Einheiten_der_Elektrotechnik_und_des_Magnetismus to be translated out of German]

I have issues with the second paragraph if the article:

• While the electric and magnetic forces may sound fairly esoteric — Esoteric? anyone who has combed their hair, used a magnet, or gotten a shock from a metallic door handle has first-hand experience of electric and magnetic forces. What is esoteric about it?
• the attractive forces between atoms in a solid that give rise to the rigidity of solids are predominantly electromagnetic — the rigidity of solids is a result of the balance of attractive electromagnetic forces and a non-electromagnetic repulsive force coming from Pauli's exclusion principle. There are repulsive electromagnetic forces, but it is impossible to obtain mechanical equilibrium using only electromagnetic means. It is still true that all the phenomena described are electromagnetic.

Also, someone complained that Maxwell's equations is hard to understand. Maybe we can design a suggested itinerary through the electromagnetism hierarchy of articles, starting from the easiest, most physically intuitive articles and advancing to more specialized topics such as Maxwell's equations.

Miguel 19:08, 5 Jun 2004 (UTC)

yes, they are unnecessarily hard to understand in Wikipedia. I will try to work on them. I like Wikipedia's depth but sometimes its accessibility is poor. Andries 19:22, 5 Jun 2004 (UTC)

You'll notice that the sentence only describes the concepts as "sounding esoteric", while in reality not being as esoteric as they sound to laymen. While it is true that hair combing and metallic door handle shock are simple expressions of electromagnetic forces, most "normal" people merely think of it as "something involving electricity that makes me go ouch", and the full concept of electromagnetism is still thought of as esoteric. -- 193.11.221.16 11:41, 16 Oct 2004 (UTC)

This article isn't esoteric, it's just extremely vague in its wording.

If you understand what to fix, go right ahead and change said wording. Otherwise, you can just copy any word/phrase in the article which may be unknown to you, paste it in the search box, click Go and read the resultant links. Or google it, if that does not suffice. Be sure to write down what is unknown to you so you can keep the question for yourself. It takes years to understand this subject, if you are working alone. Ask others for help if you do not have the time to resolve your question . Ancheta Wis 10:31, 2 January 2007 (UTC)[reply]

I have redirected electrodynamics to this article. The definition given of electrodynamics, that of "electromagnetism with quickly changing fields", is simply i

Is this not also related to electromagnetic radiation as well as electromagnetic feilds If it is only about elecromagnetic feilds then should it be merged with this article? http://en.wikipedia.org/wiki/Electromagnetic_field Alan2here 18:39, 22 October 2006 (UTC)[reply]

someones messing around, deleting the article and replacing with jokes (the jokes aren't funny either!), i don't know how to revert so i copied and pasted an older revision.

Some other science articles are starting to produce introductory versions of themselves to make them more accessible to the average encyclopedia reader. You can see what has been done so far at special relativity, general relativity and evolution, all of which now have special introduction articles. These are intermediate between the very simple articles on Simple Wikipedia and the regular encyclopedia articles. They serve a valuable function in producing something that is useful for getting someone up to speed so that they can then tackle the real article. Those who want even simpler explanations can drop down to Simple Wikipedia. I propose that this article as well consider an introductory version. What do you think?--Filll 22:46, 12 December 2006 (UTC)[reply]

The opening sentence of this article was obscure and inconsistant with all other encyclopedic sources. I have added a simpler one. An encyclopedia needs to educate the lay reader first and not begin as a vehicle to demonstrate someones "sophisticated" scientific knowledge.Lumos3 09:35, 10 January 2007 (UTC)[reply]

The first paragraph reads:

Electromagnetism is the physics of the electromagnetic field; a field encompassing all of space which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles.

There is no one field encompassing all of space; the second clause of the first sentence is just wrong. Fields only emanate from charged particles or the motion thereof (propagating waves originate from same), and are in fact only an abstraction of the effects of charged particles on each other. I think the fact that they are an abstraction should be emphasized. Somehow the description seems to say that there is one field: a substrate upon which charged particles act (also wrong). CjPuffin  23:19, 9 April 2007 (UTC)[reply]

Cj, it's true that each electron (and other charged particle) creates its own EM field, but it's also fair to say that the sum of all such fields constitutes a single field that fills all of space. (It follows from linearity of Maxwell's equations.) In fact, the more general view is that the charged particles themselves are also excitations in fields that permeate all space. The idea of field is distinct from suggesting there is some substrate containing it. Gnixon 23:23, 9 April 2007 (UTC)[reply]

Alright, I'll buy that you can consider there to be one field that is the sum of the effects of all particles, but it is sort of a stretch. When we talk about gravitational fields, do we talk about one huge field? Mostly we are concerned with fields from particles in the immediate vicinity which are strong enough to be measured. CjPuffin  23:44, 9 April 2007 (UTC)[reply]

It's definitely common to think of one field, and thinking at the same time of the many fields that sum to it is common, too. The same is true for gravity, although often the only important field comes from one object (indeed, you can consider it to come from one point mass if it's a spherical object). In E&M, where more complicated charge distributions are common, idea of one overall field is even more useful. Gnixon 23:52, 9 April 2007 (UTC)[reply]

I agree; I just don't see the point of considering the entire universe to be the charge distribution of interest and then saying that there is one field "encompassing all of space". I guess I am taking issue with the use of the definite article in that phrase. CjPuffin  00:56, 11 April 2007 (UTC)[reply]

Yeah, I could see an argument for dropping "encompassing all of space." Not sure it adds anything to have it there. Gnixon 01:12, 11 April 2007 (UTC)[reply]

W*h*f, W - A*V h - plank constant f- frenquency for example if f = 3GHz, Umax=1.35V Imax=50A then electromagnetic energy is: 1.35/2^0.5 (V)*50/2^0.5 (A)*6.626*10^(-34)(J*s)*3*10^9(1/s)=6.7*10^(-23)(J) —The preceding unsigned comment was added by 213.190.46.52 (talk) 20:31, 2 May 2007 (UTC).[reply]

I have a copy of Gilbert's "De Magnete" (Dover edition). I am 99% sure that Gilbert DID NOT discover electrostatic repulsion, surprising as it sounds. Unfortunately I don't have time immediately to check this. In any case I feel the onus to do so should fall upon the author. —The preceding unsigned comment was added by Eljeh Yendig (talk • contribs) 01:21, 4 May 2007 (UTC).[reply]

I have moved to this section material from the "abampere" article that relates to these units in general, including a list of the basic ones, along with links to separate articles containing their definitions.Fbarw 23:04, 17 September 2007 (UTC)[reply]

I have thought for a while that the electromagnetism template is too long. I feel it gives a better overview of the subject if all of the main topics can be seen together. I created a new template and gave an explanation on the old (i.e. current) template talk page, however I don't think many people are watching that page.

I have modified this article to demonstrate the new template and I would appreciate people's thoughts on it: constructive criticism, arguments for or against the change, suggestions for different layouts, etc.

To see an example of a similar template style, check out Template:Thermodynamic_equations. This example expands the sublist associated with the main topic article currently being viewed, then has a separate template for each main topic once you are viewing articles within that topic. My personal preference (at least for electromagnetism) would be to remain with just one template and expand the main topic sublist for all articles associated with that topic.--DJIndica 16:54, 6 November 2007 (UTC)[reply]

There are so many articles in this series I couldn't figure out whether this explanation/derivation exists in one of them, or not. (I can contribute some drawings etc if anyone thinks its worth the while). The explanation is easy, and I've used it before with good results (I think I found it in one of my old college texts -- Resnick and Halliday probably). It shows why, given relativity, moving electrons create magnetic fields.

We start with a column of free electrons in a given length of copper wire, say a meter lenth of it. The electrons are free because they escape their atoms' outer orbitals (definition of a metal). The electrons just wander about thereby cancelling their minus-charge with respect to the copper ions' positive charge -- all is neutral. But if they are compelled to drift because of an applied electric field along the wire, their drift velocity causes the apparent 1-meter length of ions to contract, due to the Lorentz contraction. The result is an excess concentration of electrons in the now shortened "tube" of moving electrons. This excess charge is no longer neutral with respect to the stationary column of positive ions. Thus this electrostatic-derived force represents an external force, albeit tiny, that is (i) measureable and (ii) related to the electrons' velocity. This is the so-called "magnetic" force. The vector part of it (i.e. the apparent "direction" of the force" is much harder and probably not necessary to explain. Bill Wvbailey (talk) 16:10, 24 November 2007 (UTC)[reply]

See Relativistic electromagnetism. The attribution of this to 1966 Purcell is a bit odd, since I used a text (not by Purcell -- Halliday and Resnick, I believe) in the mid 1960's that had this explanation in it. Bill Wvbailey (talk) 14:04, 12 March 2008 (UTC)[reply]

I have added a new section, Applications, I hope it helps the article. --Twicemost (talk) 16:01, 26 April 2008 (UTC)[reply]

Might be some potential. However that essay ref doesn't cut it per WP:RS. Removed. Vsmith (talk) 16:15, 26 April 2008 (UTC)[reply]

But was the removal of the entire section needed? If it was because of one of the sources, you could simply quit it. Yours was a rude edit.--Twicemost (talk) 22:19, 26 April 2008 (UTC)[reply]

You didn't answer my question. Why did you delete the entire section when you could just eliminate the essay reference, or at least discuss about that before doing that wild edit? Unless you give me a convincent explanation, I will have to assume bad faith. --Twicemost (talk) 02:47, 27 April 2008 (UTC)[reply]

Hmm... quite simply because it wasn't really about applications of electomagnetism, rather about related scientific discoveries/understandings. You are always welcome to re-add such a section - but please make it about applications. You are free to assume whatever you wish. Vsmith (talk) 03:41, 27 April 2008 (UTC)[reply]

Well, new ...;) I think it is a shame that Landau & Lifshits The Classical Theory of Fields is on the list. Mind if I ad it?YohanN7 (talk) 23:22, 15 July 2009 (UTC)[reply]

The See Also section contains a link to the Lost TV Series article. Given that the word "Lost" only appears in the See Also section and not in the article at all, and the Lost TV article doesn't contain the substrings electro nor magnet, I'm wondering what the connection is? 87.194.129.166 (talk) 20:18, 8 February 2010 (UTC)[reply]

The editor who added the link didn't give any explanation, and as you have noted, no connection is apparent; so I have reverted the edit which put that link there. Wildbear (talk) 01:18, 9 February 2010 (UTC)[reply]

Hi guys,

I've started tidying and simplifying the text of this article, and also merged the content of the Electromagnetic force in to this article using the following rationale:

• Although there are articles on electrostatic force, electromotive force, electric force, magnetic force, etc, those articles describe various subsets of Electomagnetism, whereas the Electromagnetic force is Electromagnetism.
• More than half of this content was duplicated in that article already.

There is still some duplicate information that I intend to weed out, and it might also be a good idea to reconsider the section headings too.

What do you guys think?

InternetMeme (talk) 05:30, 23 February 2010 (UTC)[reply]

Although I am behind the curve on this one, I think the merge is a good or idea (or was a good idea). Steve Quinn (formerly Ti-30X) (talk) 02:53, 9 March 2010 (UTC)[reply]

I prefer that this section has in-line citations. I think it is an important section. However, there are internal links to the main articles related to the paragraphs. It is linked really well with wiki links - so maybe that is just as effective as having in-line citations for the paragraphs. Anyone, feel free to respond or comment. Steve Quinn (formerly Ti-30X) (talk) 02:53, 9 March 2010 (UTC)[reply]

There is no motion in straight line in the space of the material Universe and there is no linear flow of time. All change, whether temporal or spatial, is continuous and the change follows rings of converging spiral. Rotations of gravitons in a unit of space can be organized into a unit of electromagnetism such as photon. The packet of rotations travels with maximum possible velocity of 'c' along the largest ring of the spiral 'c'. With distanvce from the observer velocity of transformation slows down until, at the border of the space of th Universe, it approaches '0', but only as seen by the observer in the centre of the spiral. By beinbg motivated from the perfect centre velocity of the electromagnetic unit is accelerated. This being impossible, because velocity 'c' is maximum, the additional velocity changes direction and it travels along the ring of the converging spiral which is at right angles to the direction of 'c'. Only the direction at right angles does not add or subtract anything from the velocity of 'c'. Velocity in the new direction is less than 'c' and it can vary as 'n' in (0<n<c). The velocity of 'n' decides on the spatial magnitude, called 'amplitude' of the unit of electromagnetism. Velocity of transformation on the spiral 'n' is accelerated from minimum at the largest ring to maximum in the centre of the spiral 'n'. At the maximum magnitude of 'n' the electromagnetic unit is a 'wave'. In the centre the unit has the properties of a 'particle'. Because the spiral 'n' travels with velocity 'c', dynamism of the spiral 'n' traces sinusoidal volume called 'wavelength' The same laws apply to the direction 'c'. At maximum distance from the point of observation, at the border of space, electromagnetic unit travels in the direction approaching straight line and velocity of rotation of gravitons approaches '0'. In the centre of the converging spiral 'c', velocity is maximum of 'c' but on the smallest ring 1/c of the spiral. KK (89.242.98.66 (talk) 15:38, 26 March 2010 (UTC))[reply]

You might be interested on that article. Dauto (talk) 22:26, 26 March 2010 (UTC)[reply]

Properly, "strong interaction" and "weak interaction" are preceded by "the" Sonygal (talk) 16:28, 6 October 2010 (UTC)[reply]

"Ørsted was not the only person to examine the relation between electricity and magnetism. In 1802 Gian Domenico Romagnosi, an Italian legal scholar, deflected a magnetic needle by electrostatic charges. Actually, no galvanic current existed in the setup and hence no electromagnetism was present."

The above uses the archaic term "galvanic current," which presumably is what we would now simply call a current or possibly an electrical current. In any case, the sentence makes no discernable sense. It should probably simply be removed. Dratman (talk) 04:48, 6 March 2011 (UTC)[reply]

"Magnetic poles (or states of polarization at individual points) attract or repel one another..."

Is this an allusion to the magnetic moment of an individual atom? To the spin of an electron? "State of polarization" does not seem to be a term of art in this context.

Why is some of this article written in less than an adult fashion. Much of it appears to be unsynthesized information from grade school. I know that many people will understand that it is a multi-dimensional behavioral phenomena found at different levels of cognitive understanding, but that is not fully represented in this article. Come on people, let's step up to the plate... Best regards, Steve Stevenmitchell (talk) 14:04, 18 April 2011 (UTC)[reply]

In the section as quoted above, it says "although it is now known that the photoelectric effect does not, in fact, compel one to any conclusion about light being made of "photons", as discussed in the photoelectric effect article". It's not discussed in that article, AFAICS, and I'm not aware that the lack of linkage between photons and the Photoelectric effect has been shown. Can anyone clarify before I delete that clause? --Phil Holmes (talk) 15:59, 5 May 2011 (UTC)[reply]

I vote for deletion of the clause. Dauto (talk) 21:20, 5 May 2011 (UTC)[reply]

Ive looked through almost every page linked herein, but I have failed to find anything that explains the electromagnetic phenomenon that stops things from merging with other things -- for instance, i can grab someones hand or the wall, and I wont become that object; id always remain distinct.

If I missed this, or if it was worded in a way I might not understand, I would love a link. And if its not there, why not? Surely this is an issue that would be of interest to people, since its what allows "people" instead of whatever the word for everything combined would be. Also if it is here, I think it should be made more prominent.

Sorry about the...strange wording of this but thats part of the problem; I cant even give the effect a name to search for. 74.128.56.194 (talk) 03:31, 28 June 2011 (UTC)[reply]