Talk:Near and far field
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[edit] Misleading
The text claims that the 1/r3 term is the electrostatic field term, and the 1/r2 term is the induction term.
- These should be called "magnetic" and "electric" terms; not electrostatic. Near and far field have no meaning in electrostatics
- The terms switch meanings when you talk about a current loop. The assignments referred to in the text are only about dipoles
This article is confusing, otherwise, and there's no reason it couldn't be made accessible to laymen. — Omegatron 02:22, 25 November 2006 (UTC)
- I have a BS in Physics and I have a copy of the Jackson text somewhere... I'll put this on my todo list. I'm not sure that this can be accessible to a true "layman", but it could be somewhat simpler. The main point of the article should be that the "near field" (in classical theory at least) is the part of an EM field (or also sound waves, etc) that does not propagate (though does theoretically extend "infinitely") and concentrates its energy nearby, whereas the "far" field allows the energy to propagate arbitrarily far, falling off as an inverse square of the distance (unless perfectly collimated, which I suppose is theoretically possible). - JustinWick 23:11, 7 December 2006 (UTC)
- Also I would dispute your claim that near/far fields have no meaning in electrostatics. Consider an electrostatic dipole, or quadrapole, etc. The net "flux" through a sphere centered on a monopole is finite and constant, no matter how large or small the sphere is. Any higher order moment is necessarily neutral, rendering its net flux zero - this is, IMHO, a fundamental difference (see plasma physics for an example of this), as it allows electrostatic monopoles to feel interactions from arbitrarily far away, as the amoun tof available monopoles at any given distance would typically go up as the square of the distance, balancing out the weakening of the E field. Higher order moments only interact at short range (as they fall off too quickly to be offset by the greater abundance of sources as distance goes up). But if you can find something in Jackson that states right out that near/far field are purely electrodynamic concepts, I won't argue :) Gosh, it's been a long time since I thought about any of this - hope I make sense! - JustinWick 00:17, 8 December 2006 (UTC)
