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Conductors and Coulombs law

  • Thread starter Proctologically Violated©®
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P

Proctologically Violated©®

Jan 1, 1970
0
Awl--

I seem to remember that current flow (or current density) on a solid
conductor resides *exclusively* on it's surface, ie, looking at the wire
cross-sectionally, you would see *only one* layer of electrons--not even
two, no matter how high you cranked up the voltage across the conductor.
This was explained on the basis of Coulombic repulsion, and something of
Gauss' law, which I can't quite remember.

This would mean that the current-carrying capacity of a wire is *strictly*
proportional to its circumference, not to its cross-sectional area.

But it seems to me that if the current density were high enough, and thus
the very outer layer of electron flow sufficiently crowded, indeed an "inner
layer" of electron flow should be forced, and that then the current carrying
capacity of a wire would be proportional to its cross-sectional area.

Or is it that before the electrons could be forced into an inner layer, the
repulsive forces of the electrons would be so strong as to force them to arc
into air, or across an insulating covering??

Any idears?

Thanks.
 
C

Charles Perry

Jan 1, 1970
0
Proctologically Violated©® said:
Awl--

I seem to remember that current flow (or current density) on a solid
conductor resides *exclusively* on it's surface, ie, looking at the wire
cross-sectionally, you would see *only one* layer of electrons--not even
two, no matter how high you cranked up the voltage across the conductor.
This was explained on the basis of Coulombic repulsion, and something of
Gauss' law, which I can't quite remember.

Not exactly. The current in a solid conductor will tend to flow on the
outside as the frequency of current increases. DC current is fairly evenly
distributed through the entire cross section. The term you need to look for
in order to learn more is "skin effect". Here is a good place to start:
http://en.wikipedia.org/wiki/Skin_effect

Skin effect is very prominent at high frequencies. Microwave conductors are
actually hollow (and called waveguides) because the signal only travels on
(or very near) the surface.

Skin effect IS a problem at normal power frequencies (50 or 60 Hz). It is
much less pronounced, but it still effects decisions on conductor choice and
design.

Charles Perry P.E.
 
P

Proctologically Violated©®

Jan 1, 1970
0
Charles Perry said:
Not exactly. The current in a solid conductor will tend to flow on the
outside as the frequency of current increases. DC current is fairly
evenly distributed through the entire cross section. The term you need to
look for in order to learn more is "skin effect". Here is a good place to
start:
http://en.wikipedia.org/wiki/Skin_effect

Thanks. This is not dissimilar to other recent opinions I've gotten.

But, considering only DC (before I check out your link!):

Doesn't uniform charge distribution across the cross-sectional area violate
Gauss' law (forgot what gauss' law actually sez, just remember that it dealt
with these types of problems), and coulombic constraints?
Wouldn't DC current *necessarily* start at the "skin", and 'build up"
inward, if necessary, according to these laws?
Thanks.
 
R

Roy Q.T.

Jan 1, 1970
0
I have to warn you all before i respond to this: I was chastised and
asked to leave the class and never come back after I privately showed
one of my teachers my take on Electron Flow at an atomic level using a
substrate like pictorial diagram I made employing the Electron Theory
for Semiconductors. which is, As Is, an atomic level view of anything
that conducts.

To start; I think you are thinking way too Conventional to visualize
Electron Flow in a Conductor as over the surface tension only., that
would be similar to the Magnetic Flux that would hold charge particles
in an Orbit surrounding & through the wire surface.

I suggest we try visualizing how this works with the Molecular Structure
of Solid 10 AWG for instance, the Magnetic portion of the applied EMF
would travel through this outer portion of the wire, and the current
flow ( hole transfer etc) would be totally through the thick matter of
the inner wire., then, what about stranded AWG where the electron flow &
magnetic flux is concentric to the conductor as a whole, but atomically
each strand carries it's properties mho & rho alone simultaneous to a
splice non the less ~>


<~ what happens here? is there loss or gain in the journey from source
to device? all I can say for now is: The Waveform Harmonics of the
Conventional Application we know as in 50/60Hz are (should be) much
better than with the Solid Conductors Conductivity or current carrying
capacity.

I'll review Ampacity over this,

Electrical Circuits Analysis is Purely Conventional but the inner
workings of the stuff we use in it I gather is not.

®oy
 
R

Roy Q.T.

Jan 1, 1970
0
I think the guy in the sci group where you posted also gave a very good
& clear explanation., with the change in electron or current flow paths
as you query occuring when higher frequencies are applied to the
conductor.

®
 
P

Proctologically Violated©®

Jan 1, 1970
0
Thank god for consistency!!

But for the DC case:

Doesn't a *uniform distribution* of electrons in the cross section have them
*unresponsive* to very powerful Coulomb forces, and seemingly violate Gauss'
law(s)??

It seems to me, that on *very first principles*, the electrons should at
least have a *variable distribution* in the cross section, heavily weighted
toward the circumference. No?

I will post this on a.s.p. as well.
Thanks.
----------------------------
Mr. P.V.'d
formerly Droll Troll

I think the guy in the sci group where you posted also gave a very good
& clear explanation., with the change in electron or current flow paths
as you query occuring when higher frequencies are applied to the
conductor.

®
 
J

John O'Flaherty

Jan 1, 1970
0
Proctologically said:
Thank god for consistency!!

But for the DC case:

Doesn't a *uniform distribution* of electrons in the cross section have them
*unresponsive* to very powerful Coulomb forces, and seemingly violate Gauss'
law(s)??

It seems to me, that on *very first principles*, the electrons should at
least have a *variable distribution* in the cross section, heavily weighted
toward the circumference. No?

I will post this on a.s.p. as well.
Thanks.
----------------------------
Mr. P.V.'d
formerly Droll Troll

I think the guy in the sci group where you posted also gave a very good
& clear explanation., with the change in electron or current flow paths
as you query occuring when higher frequencies are applied to the
conductor.

The rule that there is no electric field in a conductor applies to
static charges, in equilibrium. In a current carrying conductor, there
is most definitely an electric field, parallel to the direction of
current flow. In the case of steady DC, that electric field is uniform
through the conductor's cross section, so that any cross section is an
equipotential surface. Any deviation from this uniformity would be a
distortion of the applied electric field, which would result in currents
that would restore it to uniformity. This applies to a wire, or other
cylinder carrying current along its axis. If it were a conductive
sphere, it might be a little more complicated.
 
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