Talk:Electromagnetism
|
|
Holy moly there's a lot more. 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 technical 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.
| Contents |
Units of electromagnetism
[http://de.wikipedia.org/wiki/Gr%F6%DFen_und_Einheiten_der_Elektrotechnik_und_des_Magnetismus to be translated out of German]
Esoteric?
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)
Electrodynamics
I have redirected electrodynamics to this article. The definition given of electrodynamics, that of "electromagnetism with quickly changing fields", is simply incorrect. Electrodynamics refers to the effects of electromagnetism on electrically charged particles. It is often used interchangeably with the term "electromagnetism", especially since the only way we can detect electromagnetic fields is via the force they exert on particles, i.e. their mechanical effects! -- CYD
Template:Electromagnetism
I have added the template to this page, and then done a major rearrangement of the template.
I realize it is not entirely consistent with the state of the various articles, but this is what I have in mind:
- immediately under electromagnetism should be a list of layman articles about electromagnetism. The current article about electricity has just the right level of sophistication and direct application to the 'real' world. The magnetism page currently doesn't.
- I have broken the list of links into four parts, corresponding to the traditional division of the subject within physics: electrostatics, magnetistatics, electrodynamics, and electrical circuit theory. These should be physics articles.
—Miguel 20:13, 2004 Nov 19 (UTC)
The introduction of the article
Hi, I just joined the Wikipedia project, and thought I'd help. Electromagnetism is a dear subject to me.
I am a little concerned about the clarity and consistency of the first couple of paragraphs. I see, from reading the history, that this has been a contentious issue in the past. Still, I think there is some room for improvement, and since the discussion here seems active, I'd like to talk about it first.
I hope this doesn't come across as aggressive. I just want the article to be a little clearer.
The very first sentence reads awkardly. "Electromagnetism is the physics of the electromagnetic field... ." Seems self-referential to begin with, and doesn't help much if you're a 15 year old who wants to learn what electromagnetism is. It gets worse though, because then the next sentence says "The electric field is produced by stationary electric charges...", but of course the electric field can also be produced by currents and moving magnets. You might say that for this article electromagnetism is referring to electrostatics and magnetostatics where the sources are not moving, but then the article contradicts itself since it later says "Therefore, all optical phenomena are actually electromagnetic phenomena." Of course, optical phenomena are not static. Moreover, the article says "An accurate theory of electromagnetism, known as classical electromagnetism, was developed by various physicists over the course of the 19th century, culminating in the work of James Clerk Maxwell...." This, to me, clearly implies that the article is working under the pretense that electromagnetism encompasses time-dependent electric fields. In which case it is at odds with the first sentence.
Well, that's my first issue. I can try to edit the article, but I thought I'd see if an initial discussion would be fruitful.
WikipAcct 08:28, 3 Jan 2005 (UTC)