# Speed of magnetism

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

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Spacetime is not curtailed by the Universal speed limit "c"
That only applies to anything with mass. Spacetime has no mass.
Spacetime expands and is accelerating in that expansion rate.

3. ### timojinValued Senior Member

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How was it measured ? I can understand Ions moving in aqueous solution the mobility is slow,
Is that determined by resistivity ? Curious.

5. ### originHeading towards oblivionValued Senior Member

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You can determine the drift speed of an electron by the voltage and the wire dimensions and material.
Electron drift speed.

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7. ### jccRegistered Senior Member

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if electrons move that slow, why is current fast like light speed?

8. ### originHeading towards oblivionValued Senior Member

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Because the electric field that propagates through the wire is moving close to the speed of light, the individual electrons are not, they are going very slowly (in the direction of the current).

9. ### Fraggle RockerStaff Member

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James is an actual professional scientist, one of the few we have on SciForums. He knows what he's talking about.

10. ### jccRegistered Senior Member

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EM field propagates at light speed? How?

What's the source of the moving EM field?

11. ### originHeading towards oblivionValued Senior Member

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A voltage potential.
Here is a common one:

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

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energy is limited by mass, if mass is involved, motion slows due to the existence of this mass.[ plasma and mass are two separate elements of mass, phasing in a single moment is key] pure energy is not bound, it travels as fast as conceived. but then again, QP claims energy doesn't " move " but exist in a state at that moment. everything is in levels, each level builds the next. best to comprehend levels of nature and it's process and functions.

13. ### jccRegistered Senior Member

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Let's look at a flash light, the voltage is 3 V, the electrons are moving in the wires at low speed, the light comes out instantly.

How em field propagate in the wire? Isn't the only thing that moves is electron in the wire? Is the electron carrying the em field?

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

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i would suggest you looking into faraday's work, then ponder this, then maybe make your comments; but until then you're just causing problems for yourself. agian, please make this effort. i have no problem in explaining when sincerity is involved, but i have no interest in pathetic, low level minded response that the sole intention is just to ridicule, only because one believes they're some kind of intellect.

15. ### jccRegistered Senior Member

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Thanks, I an sincerely about my science questions. 100%.

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

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except you decided to make this remark: but there were no good answers.
shrugs.

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

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for understanding, must come acceptance. the question is meaningless. but anything i state may not be an achievement, considering the mismatch between our intellects.

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Yes, obviously this character is out to carry on from where he left off before his moderation.

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

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yes, just comprehend what was explained. SHRUGS.

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One can only surmise a problem in either [1]Inability to understand, [2] Not mature enough and mind not developed enough to understand, [3] You have an agenda blinding you to all logical answers,[4]You are trolling.
Which is it?

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

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jcc:

Suppose you turn on the ceiling light switch in your room. The light that it activates is probably several metres away from the switch, but it turns on practically instantly when you flick the switch. But if you calculate how long it would take an electron to flow from the switch to the light, it turns out to be (from memory) at least several minutes. So why does the light turn on straight away?

A rough picture is this: when you turn on the switch, you start pumping in electrons at one end of the circuit and extracting them from the other end. When an electron is pumped in, it repels other electrons that are already sitting in metal of the wire, which then bump other electrons. This process creates a rapid "wave" that passes along the wire so that almost immediately you put an electron in one end another one pops out the other end. And, almost immediately, the electrons that were in the light-bulb all along are set into motion, lighting the bulb.

In the case of an electromagnetic wave, the electric and magnetic fields induce one another very rapidly as they change, creating a wave that propagates at the speed of light. This is shown by Maxwell's equations of electromagnetism.

If you're talking about electricity in a wire, then you need only worry about the electric field. Turning on the switch creates, almost immediately, an electrical potential gradient in the wire, which sets up a more-or-less constant electrical field through the wire. That doesn't quite happen at the speed of light, but it's near enough.

All electric and magnetic fields are ultimately caused by electrically charged particles.

The electrons move very slowly in your flash light. But what is important is not the electrons themselves but the energy they carry to the bulb.

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23. ### Q-reeusBannedValued Senior Member

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Wrong on both counts. Electrical signals propagate along a transmission-line as a conduction-charge/field coupled surface wave - not through the wire proper. Propagation through a typical metallic conductor is at much less than the speed of sound and at any rate is severely exponentially attenuated as a function of penetration depth. Hence e.g. radio waves reflect from a metallic sheet.

Also, actual conduction electrons average speed, in the direction of current flow, is a large fraction of the Fermi velocity typically ~ 10^6 m/s. Much less than c but many orders of magnitude greater than the long outdated Drude model predicts. My first postings at SF were on this topic - we clashed numbers of times in that thread. Evidently you never changed your position. As I noted back then, the fact many textbooks and websites perpetuate the Drude model notion of 'electrons crawling along at a snail's pace' is sad. Any decent solid-state physics textbook sets it right. Here's an online easily digestible example:
http://www.phys.ttu.edu/~cmyles/Phys4309-5304/Lectures/Lecture06e FEG Transport3.ppt
I'll even spare you the trouble of plowing through it all - just check out the plain summary p42.