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

[Tom Watson]

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)

[Mark]

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

[gene]

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

[Doug Miller]

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.

[Mike Marlow]

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.

[Kerry Montgomery]

larger portion of the electrons travel on the surface of the wire (skin effect, see

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

[JP]

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.

[Lew Hodgett]

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

[Tim Daneliuk]

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 [e-mail] PGP Key:

[Tom Watson]

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 >I had a conversation with a friend of mine today who has a masters in

tjwatson1ATcomcastDOTnet (real email)

[dpb]

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...

--

[Tim Daneliuk]

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

[Tim Daneliuk]

magic dwarfs with bad tempers and worse breath ...

[Tim Daneliuk]

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.

[dpb]

As most of those postings noted, the "skin effect" is really only of significance and high frequency (far above the 60 Hz AC). The solution of Maxwell's equations is dependent on the material and changing the core material changes the behavior as well. A combination of materials _might_ be effective, but certainly until very recently the cost differential of manufacture w/ multiple materials far outweighs the benefits. It _might_ be getting to the realm of reasonable, but while I've not investigated it as a real possibility, I really doubt even yet we're to that point on material costs relative to other costs.

The electric utilities spend a great deal on research and I spent a sizable fraction of my career in the utilities business working w/ EPRI (Electric Power Research Institute, a utility-funded R&D organization) in the I&C and Transmission & Distribution areas and if the concept was considered very high on the list, it would have received funding for at least theoretical work. To the best of my knowledge it hasn't.

Where we could _really_ make a savings would be to get practical near-room-temperature or at least not near-absolute-zero superconductors--they're making progress, but a ways to go yet.

[Tom Watson]

Read the Wall Street Journal article of last week, which references a Science article of previous.

They are using MRE technology to direct a useful power across at least three meters without wires.

Damned interesting.

I don't think that is only about frequency - but it certainly inhabits the concept of specific resonant frequency.

Regards,

Tom Watson

tjwatson1ATcomcastDOTnet (real email)

[Tim Daneliuk]

This is, in fact, done in some cases. I recall one 50KW broadcast transmitter wherein a colleague of mine had to replace the tuning coils. Instead of paying a small fortune to the manufacturer for what he needed, he made his own out of ordinary copper water pipe - exactly because the very high currents involved were carried on the surface of the coil "winding" anyway. Note that this is not even particularly high frequency stuff, the AM broadcast band running from about 500-1500 Khz.

Interestingly, he had to do this because the station had purchased a used transmitter (50KW broadcast transmitters are NOT cheap) but it was tuned to the wrong frequency. He reengineered it himself by changing the aforementioned coil and a few other parts and got the thing to sit right on the frequency they needed. As I understand it, they passed FCC proof-of-performance handily.

[Tom Watson]

The problem with those who are educated is that they have been trained off the obvious.

Their predilection is to assume the veracity of the precedent, without question.

I'm asking you to revisit the fundamental assumptions.

Regards,

Tom Watson

tjwatson1ATcomcastDOTnet (real email)

[Tom Watson]

You are moving towards my theory on this, Tim.

Regards,

Tom Watson

tjwatson1ATcomcastDOTnet (real email)

[Tim Daneliuk]

I'm not sure where you're going with this. Skin Effect is not an "assumption" - it can be calculated and probably even measured. From

we get this (near the end of the article):

In copper, the skin depth at various frequencies is shown below.

frequency depth

60 Hz 8.57 mm 10 kHz 0.66 mm 100 kHz 0.21 mm 1 MHz 66 µm 10 MHz 21 µm

In Engineering Electromagnetics, Hayt points out that in a power station a bus bar for alternating current at 60 Hz with a radius larger than

1/3rd of an inch (8 mm) is a waste of copper, and in practice bus bars for heavy AC current are rarely more than 1/2 inch (12 mm) thick except for mechanical reasons. A possible solution to this problem consists of using cables with multiple insulated conductors. A thin film of silver deposited on glass is an excellent conductor at microwave frequencies.

----------------------

Note that multi-wire transmission lines for very high power shortwave transmitters (and their attendant power supply lines) make use of this fact today. So .... where are you going, I wonder ...