# Speed of magnetism

Discussion in 'Physics & Math' started by Syzygys, Nov 20, 2006.

1. ### Q-reeusBannedValued Senior Member

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Pseudo-scientific word salad nonsense - worse than what jcc puts out, and that's saying something.

3. ### James RJust this guy, you know?Staff Member

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Electrical currents are carried in the body of a conductor, not on the surface. This is experimentally verified by the fact that the resistance decreases in proportion to the cross-sectional area of a wire, and not in proportion to its circumference.

As for the electron drift velocity, the relevant formula is:
$J = nev_d$,

where $J$ is the current density, $e$ is the electron charge, $n$ is the number of electrons per unit volume in the conductor and $v_d$ is the average drift velocity of the electrons for the given current density.

You can confirm the "snail's pace" for yourself using this formula.

5. ### Q-reeusBannedValued Senior Member

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Chalk and cheese James. I try and be careful to preface by giving relevant context. That I did in #40. Please read my second sentence there carefully - taking note of the quote it was referring to. Clearly the context is transmission-line propagation. Yes of course in DC situation, or even in many low frequency AC situations, conduction very rapidly stabilizes, after initial transients die down, to being uniform or close-to uniform through-conductor.
The drift current formula you give is one that, as explained in that article I linked to (worth actually reading!), assumes the long outdated crude Drude model. Physicists knew better by the late 1920's. Your simple formula implicitly assumes there an n equal to the so-called 'free electron' density, rather than the vastly smaller actual conduction electron density. I continue to be amazed by the longevity of Drude picture. Maybe because it happens to roughly 'work' owing to a cancellation of two conceptual errors. The Sommerfeld picture is not perfect but was a breakthrough in that it correctly accounted for certain properties that Drude model failed badly to predict.

7. ### James RJust this guy, you know?Staff Member

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Q-reeus:

Thankyou for your response. It prompted me to do a little online reading, and it reminded me of some vaguely-remembered stuff I was supposed to have learned at one stage.

Interestingly, the Drude formula for the electrical conductivity of a metal turns out to be the same as the Sommerfeld one. But, as you say, it's right for the wrong reasons. Drude's model is classical and assumes a large number of conduction electrons moving slowly, whereas Sommerfeld's model is a quantum one that predicts few conduction electrons moving fast. And yes, the Sommerfeld picture explains things the Drude model could not - as one might expect from a quantum vs a classical model.

Thanks Q-reeus. I (re-)learned something today. My apologies for presuming to correct you when you obviously had a better understanding than I did.

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8. ### Q-reeusBannedValued Senior Member

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No problem James - as long as we can all learn from each other in a good-natured spirit being right or wrong is secondary to acting respectfully and objectively. Best.

9. ### krash661[MK6] transitioning scifi to realityValued Senior Member

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well , i'll say my usual:according to whom?. which is never answered for some odd reason.

shrugs.
then i would suggest evolving your knowledge in the field of extremely high energies and the cosmos; instead of using electrical engineering.

shrugs again.
then after that, speak from actual experience. even if it's at least from a position of a backyard scientist. but we know that is no where near obtainable for you as you click on whatever wiki link, correct ?
i'm also going to reiterate:but a lot of them take the ego deflation very hard when they find out not only how much they don't know, but how much they're not capable of understanding.but anything i state may not be an achievement.
so all in all.

SHRUGS, WHO CARES,CORRECT ?

10. ### krash661[MK6] transitioning scifi to realityValued Senior Member

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i would also be interested in what you understand of theorems. but it's obvious that's far advance to even mention.

shrugs.

11. ### krash661[MK6] transitioning scifi to realityValued Senior Member

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also i'm not allowed to comment on the "
Why do most people find science boring? " thread. it appears only because i questioned an so- called moderator; whether scientific knowledge, and as bruce elaborates, scientific honesty was a factor

shrugs.
what's amazing for me is, i now, fully, comprehend the extensiveness of complaints of the fictitiousness, double standards of the moderation here and within.

all in all, all these public science sites are NOTHING MORE THAN the cesspool they manifest themselves to be.

SHRUGS. now what ? am i banned ?

shrugs agian.

Last edited: Jul 26, 2015
12. ### Q-reeusBannedValued Senior Member

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Have I managed to push someone's button? Guess so.

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What?

14. ### originHeading towards oblivionValued Senior Member

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Yeah, I was sloppy on that.

I did not know this - thanks. That is a nice overview presentation.

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15. ### Q-reeusBannedValued Senior Member

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My pleasure origin. It's hard to blame folks for thinking differently given how many sources still present the old classical or 'hybrid' viewpoint. A site like HyperPhysics.com gets it half-way right with a quasi-Drude model: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html#c1
They correctly note the free/conduction electron speeds are around the Fermi velocity, but assume a picture where totally random motions of all 'free electrons' are slightly perturbed, between frequent collisions, by an applied E field. Hence a tiny 'random walk' net average drift velocity. Applying that scenario as they do works in the case of electrical conductivity for reasons given before. In the Sommerfeld picture, not only are the conduction charge numbers comparatively small, but owing to how an applied E distorts the Fermi surface, their emission directions are not entirely random as in Drude or quasi-Drude picture, but heavily biased in favor of the applied E field direction. And that's the real key to high conduction charge mean 'drift speeds'. If emissions were random, conductivity would be far worse than in quasi-Drude model given the far smaller number densities.

A fellow by the name of Norris Preyer put out a number of interesting articles and animated 'movies' showing the important role of surface charges in establishing, 'after the switch is closed', a final DC conduction regime, following an initial very rapidly oscillating decaying transient regime. Unfortunately the original website including the animated stuff seems now defunct, but here's the sites anyway in case they work for some:
http://galaxy.cofc.edu/pubs/tpt99
http://galaxy.cofc.edu/circuits.html
http://galaxy.cofc.edu/rcircuits.html (best - includes retardation)
galaxy.cofc.edu/pubs/AJP01002.pdf
http://galaxy.cofc.edu/pubs/AJP01187.pdf (best - includes retardation)
http://galaxy.cofc.edu/refs.html
The following link to his AJP article does work, but is not the best example:

16. ### el esRegistered Senior Member

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317
Post #42 applies more to DC.
For AC of higher frequencies tubular conductors can be used due to skin effect.

17. ### billvonValued Senior Member

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The voltage differential creates a gradient. Electrons move through the conductor under the influence of that gradient. The gradient propagates at close to the speed of light, even though the electrons do not.
Yes.
Not quite. A lot of electrons represents charge. Charge causes an EM field (if the situation is static, as in this case, just an E field.) Electrons in the wire move under the influence of the E field.

18. ### krash661[MK6] transitioning scifi to realityValued Senior Member

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shrugs, and yet no answers to my buttoned pushed questions

huh.............. just an elementary remark.

in your own pathetic, double standard words; would that be " trolling " ?

Last edited: Jul 28, 2015

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20. ### Q-reeusBannedValued Senior Member

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Totally lost it. My strong advice - stay off the booze http://www.sciforums.com/threads/what-minimum-distance-is-red-shift-detectable.91386/#post-3314178
You are a bitter, twisted, likely deranged individual that has been allowed to rampage free at SF way too long imo. And I note who your close buddies at SF are.

Last edited: Jul 29, 2015
21. ### krash661[MK6] transitioning scifi to realityValued Senior Member

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shrugs, and yet no answers to my buttoned pushed questions

huh.............. just an elementary remark.
in your own pathetic, double standard words; would that be " trolling " ?
also in that link, i also stated :but still. increase your intelligence. shrugs.
and yet, i'm such an assshole that i have no friends nor buddies.
but i am curious as to whom you think they are since this is your claim.

22. ### billvonValued Senior Member

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No. Trolling would be posting pseudoscientific nonsense, then attacking and belittling anyone who disagrees with said pseudoscience. Trolling would involve claiming that other posters are not smart enough to understand your brilliant but unconventional theories, and proving this by calling people "pathetic" and "low level minded" rather than making any attempt to discuss said pseudoscience. Rather than explanations, when pushed, a troll might reply

shrugs

shrugs

shrugs again.

That would be a great definition of trolling.

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23. ### krash661[MK6] transitioning scifi to realityValued Senior Member

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is it not amusing when data ,that is not acknowledged, is claimed to be pseudoscientific nonsense * , belittling ? including the insulting of science and scientist ? where was the discussion ?
i'll reiterate again: but a lot of them take the ego deflation very hard when they find out not only how much they don't know, but how much they're not capable of understanding.but anything i state may not be an achievement.

* EDIT-
i apologize, the actual words used was : Pseudo-scientific word salad nonsense

Last edited: Jul 29, 2015