What is happening in those wires?

crutschow

Joined Mar 14, 2008
23,487
Gerry, you seem to have an obsession with what exactly the electrons are doing in a circuit, which is a hill-of-beans as far as the operation of a circuit is concerned.
Otherwise, it's the equations describing the resulting currents, such as Ohm's law, and the Kirchhoff and Thevenin relationships that are important to understanding and designing circuits.

You keep looking for flaws in the analogies, and there will always be flaws, since they indeed are analogies.
To know exactly what happens to the electrons, you need to study quantum electronics.
When you done that, that get back to us with your questions.
Otherwise you are just trolling us. :rolleyes:
 

Thread Starter

Gerry Rzeppa

Joined Jun 17, 2015
170
My model is not contrary to their model.
You are correct. I realized that I had chosen the wrong word and made the correction before you quoted me in your message above. I find Chabay & Sherwood's model, not contrary, but more comprehensive because it answers qualitative questions that the purely quantitative approach does not.

I leave you with this timeless wisdom: 'Voltage loves an open; current hates it.'
Excellent example. If we leave the movements and effects of surface charges out of the picture, the student is led to an unanswerable conundrum: How can there be a potential difference across an open switch, since E=IR and I is zero?

If you can actually wrap your mind fully around that statement, it will unlock electronics for you...
That is exactly what I'm trying to do. But I must say that the textbook by Chabay & Sherwood, and articles like these...

https://matterandinteractions.org/wp-content/uploads/2016/07/circuit.pdf
http://www1.astrophysik.uni-kiel.de/~hhaertel/PUB/Quality-Electricity.pdf
http://www1.astrophysik.uni-kiel.de/~hhaertel/PUB/Voltage-PdN.pdf

...are helping me more than the disputatious and sometimes demeaning responses I've been getting here.

To know exactly what happens to the electrons, you need to study quantum electronics.
When you done that, that get back to us with your questions.
Otherwise you are just trolling us.
I have been instructed by posters here to "get a degree in Electrical Engineering" and to "study quantum electronics" before asking further questions. Well, fair is fair, and I would request that you folks spend a few minutes skimming the papers I've linked to above to better understand my "educator's perspective" on this subject (which, judging by the materials referenced above, is hardly unique to me).

I'm sorry, crutschow, that you feel like you're being trolled. But this is a public forum, and it is hard to say whether all the "lurkers" (who read but do not comment) feel the same way. And an unanswered post like this (earlier in this thread)...

I have a feeling that there is a lot of "this is such basic stuff" attitude in this thread, without looking deep enough.... My approach is: intuitively there will be electric field between the two terminals - there should be some electric field between parts of different voltage. For electric field to exist, there has to be more charges at one side than the other. The two terminals have capacitance (is mutual capacitance the term?), therefore one terminal will have a bit more charge on the surface than the other, that induces the electric field. So the "inside" of the wires remains the same, but the outer layer exhibits some minor change in amount of electrons. Can you guys tell me if you agree with this, and such explanation suits to the further question, what happens to two wires connected to an AC source? That is, the capacitive charge moving back and forth, and leaving excess electrons on one terminal or the other?
...suggests that at least one other person thinks the matter worthy of further discussion and investigation. The articles I've referenced may be of no interest to folks like BobaMosfet and crutschow, but they might be treasured by people like kubeek. Different strokes for different folks; we all think and learn differently, and a public forum like this should have room for all kinds of sincere students.
 
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shortbus

Joined Sep 30, 2009
7,074
Could it be that Chabay & Sherwood couldn't understand or go along with the normally used "water" analogy? One of those "dare to be different" moves. If you replace their (paraphrasing here ) pile up of electrons for volume of water, they are very similar or could even be called the same.
 

Thread Starter

Gerry Rzeppa

Joined Jun 17, 2015
170
Could it be that Chabay & Sherwood couldn't understand or go along with the normally used "water" analogy? One of those "dare to be different" moves. If you replace their (paraphrasing here ) pile up of electrons for volume of water, they are very similar or could even be called the same.
Chabay & Sherwood have rejected, not only the "water" analogy, but all such analogies in favor of a prosaic description of what actually happens at the atomic level. This is how they put it:

"It has been common to use hydrodynamic or other analogies in the teaching of electricity, but these analogies can be misleading. Another advantage of [our] new approach is that it is based directly on the fundamental Coulomb interaction rather than on a necessarily inaccurate analogy to some other physical process." (https://matterandinteractions.org/wp-content/uploads/2016/07/circuit.pdf, page14)

It seems that the idea of any kind of electron imbalance in a circuit is anathema to many on this forum (though such imbalances are readily accepted on the opposing plates of charged capacitors, on the terminal ends of healthy batteries, and inside energized vacuum tubes). Therefore, to be clear (and hopefully less heretical) let me point out that Chabay & Sherwood (and the others I have referenced) begin by distinguishing the field-causing electrons on the surface of a conductor from the "current-carrying" electrons in the body of the conductor. The pile-ups in question involve only these surface-electrons, and the sequence of events when a circuit is completed is:

(a) an instantaneous rearrangement of surface electrons resulting in
(b) the instantaneous generation and/or adjustment of electric fields that cause
(c) the relatively slow movement of electrons inside the conductor that we associate with the term current.

If any of you don't have the time or interest to read the whole paper by Chabay & Sherwood, please skim the first three large-type pages of this article...

http://www1.astrophysik.uni-kiel.de/~hhaertel/PUB/Voltage-PdN.pdf

...so we can at least be talking about the same thing.
 

Wolframore

Joined Jan 21, 2019
1,314
Hey Gerry that’s an interesting way to look at it and it would explain the voltage drops you can measure across resistors. I like it but it’s kind of stuck in time a little bit.
 

nsaspook

Joined Aug 27, 2009
6,473
Could it be that Chabay & Sherwood couldn't understand or go along with the normally used "water" analogy? One of those "dare to be different" moves. If you replace their (paraphrasing here ) pile up of electrons for volume of water, they are very similar or could even be called the same.
This conversation with the OP is not about Chabay & Sherwood (A proper physics correct book that explains surface charge transients and steady state configurations in wires nicely).
https://forum.allaboutcircuits.com/threads/drift-velocity.63766/#post-489233
It's completely about trolling forums and newsgroups for IMO some strange reason that has persisted for years..
 
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oz93666

Joined Sep 7, 2010
672
I haven't read this whole thread ...

But of course there are PHYSICAL changes in the wire ... the atoms of the wire move further apart ... That's a physical change ... they also wobble faster.

(passage of current heats the wire)
 

Wolframore

Joined Jan 21, 2019
1,314
It’s like asking what happens when you drop a ball. You can say it moves away from your hand or it falls and stays on the ground once it bounces a few times. I believe the real confusion here is that the OP switches back and forth from DC to AC behavior while his model is a DC model.

There is no accumulation of free electrons at the cathode of a dc model. They get pulled by the potential from the other components. Then the holes are filled by the battery.
 

nsaspook

Joined Aug 27, 2009
6,473
It’s like asking what happens when you drop a ball. You can say it moves away from your hand or it falls and stays on the ground once it bounces a few times. I believe the real confusion here is that the OP switches back and forth from DC to AC behavior while his model is a DC model.

There is no accumulation of free electrons at the cathode of a dc model. They get pulled by the potential from the other components. Then the holes are filled by the battery.
There is no confusion at the OPs end, every detail here was discussed ad nauseam years ago. Coulomb interaction, electron mobility and surface charge are all well known and understood effects in electrostatics.
https://electretscientific.com/author/ajp/1962ajpv30n1pp19-21.pdf
It's just that they are usually not explored IRT low voltage DC circuits (in HVDC circuits the effects can be important) but the effects of surface charge are important in driving current even if the actual physical differences along the good conductor from the effect is only a few atoms (the Coulomb force is monstrously strong and electron mobility in a good conductor is very high) from the 10^19 electrons in those wires at 1A.
http://adsabs.harvard.edu/abs/1996AmJPh..64..855J


https://iopscience.iop.org/article/10.1088/0143-0807/28/3/020
 
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Wolframore

Joined Jan 21, 2019
1,314
Well I'm glad we ignore some of these things.... otherwise we would be constantly impeded trying to calculate everything even when the tolerances introduced in PPM and when real life components will introduce even more variations... I'm having fun with Thevenin calculations for base bias... ugh so much fun...

So basically it's right hand rule of current direction, causing magnetic charges to occur... i get the concept.
 

Thread Starter

Gerry Rzeppa

Joined Jun 17, 2015
170
I think my question has been answered, so we can stop now.

THIS WAS THE QUESTION:

Given the circuit below, with the capacitor previously charged to 100 volts and the resistor large enough so that full discharge will require about an hour:

cap 4.jpg

Please describe the physical changes that take place in wire A and wire B during the discharge period.

AND THIS IS THE ANSWER (in brief, according to Chabay & Sherwood, et al):

When the "B" and "A" legs of the circuit are connected to the capacitor:

(a) there is an instantaneous rearrangement of surface electrons resulting in...
(b) more electrons on the surface of the "B" conductor (and near the lower end of the resistor), and fewer electrons on the surface of the "A" conductor (and near the upper end of the resistor), which...
(c) create the various electric fields necessary to stimulate and sustain the slower movement of electrons inside the conductor that we associate with the term current.

CLOSING REMARKS:

I am satisfied with that answer (and I especially like the way it explains how there can be a potential difference across an open switch connected with long wires to a battery, even when the "I" in "E=IR" is zero).

I do, however, wonder why something like the above wasn't proffered as an answer earlier in this thread, which could have reduced it to a mere two or three posts (rather than the six rambling pages to which it has grown).

Thank you all, nevertheless, for your time and interest.
 
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Thread Starter

Gerry Rzeppa

Joined Jun 17, 2015
170
You do know their work is copyrighted so you can't put it in your book?
I don't think that will be a problem since I'll only be making use of their facts and ideas, which can be traced to the earlier work of Hermann Härtel, who built his ideas on a foundation of facts and ideas laid by WiIhelm Weber, who wrote 'way back in 1852. Facts and ideas, as I'm sure you know, are not the proper objects of copyright and/or patent protection. In any case, I'm certain that a simple appeal to the Fair Use doctrine would be sufficient to obtain a summary dismissal of any legal challenges. So I don't foresee any difficulties, but thanks for your concern.
 

MrChips

Joined Oct 2, 2009
19,379
I am sorry to say your conclusion is false.
(a) there is an instantaneous rearrangement of surface electrons resulting in...
This is flawed since it takes a finite amount of time to rearrange the electrons.
 

Thread Starter

Gerry Rzeppa

Joined Jun 17, 2015
170
I am sorry to say your conclusion is false.
(a) there is an instantaneous rearrangement of surface electrons resulting in...
This cannot happen since it takes a finite amount of time to rearrange the electrons.
instantaneous: adjective: occurring or done in an instant
instant, noun: a very short time (as the time it takes the eye to blink or the heart to beat).

Chabay & Sherwood: "We know experimentally that the appropriate surface charges are established very rapidly in a simple resistive circuit, because we do observe a steady state almost immediately after connecting the circuit or bending the wires." (https://matterandinteractions.org/wp-content/uploads/2016/07/circuit.pdf, page 8).

Hermann Haertel: "When a voltage source is applied to a circuit, the change in charge distribution travels like a wave-front through the circuit. This conclusion follows from the principle that there is no action at a distance but that a change can only be transmitted continuously in space and time. (Fig. 2.22. Change of Voltage) Knowing the speed of light, it can be estimated that for a circuit of a length of 1 meter, the time to reach a new state of equilibrium is something like 10^-8 seconds." (http://www1.astrophysik.uni-kiel.de/~hhaertel/PUB/Quality-Electricity.pdf, page 29).

surface charges on conductors.jpg

(www1.astrophysik.uni-kiel.de/~hhaertel/PUB/Voltage-PdN.pdf, pages 4-5) Note that this particular rearrangement of surface charges does not require a closed circuit.
 
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MrChips

Joined Oct 2, 2009
19,379
Consider what happens when you bring the metallic conductor towards the charged plate.
Charge distribution already occurs even before the conductor makes contact with the plate.
 

Thread Starter

Gerry Rzeppa

Joined Jun 17, 2015
170
Consider what happens when you bring the metallic conductor towards the charged plate.
Charge distribution already occurs even before the conductor makes contact with the plate.
No doubt. But more significantly when contact is made. Surface charge distribution and re-distribution is very dynamic and serves at least three purposes (as nsaspook pointed out above):

surface charges three roles.jpg

What's your point?
 
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