ee's please reply - (or those who think think they may know)

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I had a conversation with a friend of mine today who has a masters in electrical engineering.
This degree was conferred by the same school that I went to (Villanova) about a hundred years ago, so I must inherently trust him.
Yet...
The question that I asked him, which I thought to be simple enough, was - do the electrons travel down the circumference of the wire, or do they travel through the core of the wire?
He told me that that is an unknown.
This was very surprising to me as I thought that it would be easily tested.
Could we not create a wire of a core of inert material and coat it with a conductor and measure the difference between a wire of the pure element and that of the coated variety?
This seemed to be not within his reckoning.
The reason that it is important, to me, is that, if the electrons only travel on the circumference, that circumference may be folded into a smaller section than that described by the original, and wires would not have to be so thick.
Would y'all please try to help me out of this conundrum?
Is my friend a poseur?
Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1 /
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Tom Watson wrote:

IIRC, they tend to gravitate towards the circumference. Google 'eddy currents' and you might turn up something. It was taught to me this is one of the reasons that stranded wiring (in heavy duty applications) works better. Obviously, stranded is easier to work with, also. I'll watch this thread to se if I'm on the right track....                             Mark
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When I took grounding and shielding from Ralph Morison the first thing he said was that you need to remember two things 1) all electrical energy is contained in fields. 2) ohms law works.
the electrical field is defined by the boundaries of the conductors.
GeneK
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You must have gone the same school as me, years ago.
Pete
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No, I don't think your friend is a poseur, but I don't think he completely understood the drift of your question, either.
In an alternating-current circuit, electric *charge* travels on the surface of the conductor, and to some depth below the surface. Google on "skin effect" for more information, or ask your friend; I'm sure he must be familiar with the concept. Moving electric charge is not quite the same as moving electrons, and if you phrased your question specifically with regard to electrons, he may not have made the connection to skin effect -- especially if you didn't tell him why you wanted to know.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Can't say anything about your friend, because I've never met him. But... I do recall from days gone by, that as frequency increases, skin effect becomes more of a factor. Seems to me that at least at one time, it was believed that electrons only traveled the skin at these high frequencies.
--

-Mike-
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It's been a while, but my remembrance is that as the frequency increases, a larger portion of the electrons travel on the surface of the wire (skin effect, see http://en.wikipedia.org/wiki/Skin_effect). So, your idea may work for high frequencies, but probably not for low frequencies/DC. Some high frequency circuits (coils, particularly) are built using Lenz wire (spelling?) which is made up of many strands of very fine wire. Since the high frequency current flows along the surface, and there's a lot more surface to the many strands, this bunch of wires can conduct more current than a single wire of the same outside diameter could. Real ee's may be able to offer a more correct explanation. Kerry
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1st point: this is not a woodworking discussion
You did not specify if the current was AC or DC. If it's DC the current would more or less evenly spread throughout the wire. If the current is AC Maxwell's equation's force the electron's to travel on the outer surface of the wire, with a quick lowering of current density as you got closer to the center. The AC model is fairly certain, the DC model is almost entirely based on theory. Your folded wire would still have the electrons travelling on the outer edges while carrying an AC current. I see no problems with the answer your friend gave based on the question you asked.
BS in physics and electrical engineering.

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JP wrote: ...

...
And, the effect is used in higher-end of the HV transmission lines -- the three conductors relatively close together in a triangle are a "virtual" wire acting in concert...
--
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Tom Watson wrote:
> The question that I asked him, which I thought to be simple enough, > was - do the electrons travel down the circumference of the wire, or > do they travel through the core of the wire?
Good question.
You could compare a solid conductor V a tubular conductor made of the same materials and of the same length at various currents and frequencies.
To paraphrase an old chief engineer of mine, "Give us a year and $500K and we will define the problem for you."
Lew
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Tom Watson wrote:

It depends on the frequency of the signal, IIRC. As frequency rises the tendency is conduct along the surface of the conductor. This is (if I can remember that far back) called "skin effect". ---------------------------------------------------------------------------- Tim Daneliuk snipped-for-privacy@tundraware.com PGP Key: http://www.tundraware.com/PGP /
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Tim Daneliuk wrote:

P.S. There are no electrons, electricity is carried by teeny little magic dwarfs with bad tempers and worse breath ...
--
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Tim Daneliuk snipped-for-privacy@tundraware.com
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*trim*

Those teeny little magic dwarfs smoke a lot, don't they?
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No, they don't usually smoke at all.
Until they all stop working for a massed fag break, where they now have to go outside to do it.
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Andy Dingley wrote:

The trouble is that when they do that you can't get them to go back to work.
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--John
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There have been a number of responses so far, many of which reference the "skin effect" - why the hell do we continue to produce wire that has a core of the same conductive capacity as the surface, at great cost, when we might manufacture a wire of a cheaper core material, with the surface conductor at optimum.?
Wouldn't it make more sense to create a wire of a cheap core, with a surface at optimum? We could have gold plated wires that would be cheaper than solid copper.
wrote:

Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1 /
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Tom Watson wrote:

I think this is all about frequency. At 60hz I don't believe this buys you much, but at Mhz/Ghz freqs it might ...
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Tim Daneliuk wrote:

Oh, in a related note ... In my misspent youth, I installed/repaired High Frequency Single Sideband Radios for fishing boats in Alaska.
Many of these vessels were wooden and ground is rather important when designing HF radio antennas. We could typically find good ground at the heat exchanger in the bilge of the ship which was metal and in contact with the ocean.
The problem always was that these are typically pretty far away (20-100 feet) from the wheelhouse. If we used wire to get to ground, that wire then actually became a radiator of radio energy - which is not what you want from a ground.
So, we used copper flashing which was very thin but *Wide*. At HF frequencies, area turns out to be a big deal for ground planes. In the worst case, we'd use 00 or even 0 welding cable to get to a real ground because - IIRC - the effective area of a wire is something like 2-3x its diameter.
--
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You are moving towards my theory on this, Tim.
On Fri, 15 Jun 2007 20:24:33 -0500, Tim Daneliuk

Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1 /
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Look up wave guides, as frequency reaches Giga hertz range the current passes along the skin. Radar frequencies actually travel inside a hollow conductor that "funnel" the signal from the electronic circuit output to the antenna.
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