Electron Re-arrangement and Flow in Power Lines

[Gerry Rzeppa]

I've been doing some bedtime reading in Chabay & Sherwood's Matter & Interactions textbook (https://www.amazon.com/gp/product/0470503475/?tag=pfamazon01-20) and have come across some interesting tidbits. Here they are:

I've always pictured electrons pushing each other through a wire, kind of like peas through a drinking straw. I thought this was a good way of explaining how, for example, a ceiling light comes on immediately even though the drift speed of electrons is relatively slow. Turns out Chabay and Sherwood say it isn't so:

And so I think, okay, let's assume they're right. So what does the pushing? Chabay and Sherwood say it's electric fields that push the electrons through the wires, and that these fields are caused by particular, non-uniform arrangements of electrons on the surface of the wires -- electrons distinct from the "current carrying electrons" deeper inside:

They even ask the student to draw a map showing the arrangement of surface charges in a simple circuit:

And I think, Okay, that sounds reasonable. (Bear in mind that there's a lot of math between these excerpts where they make their case in a more quantitative fashion.)

Then they explain why our ceiling light behaves as it does:

And that's where, I think, they fumble the ball a little. Why? Because they say, "the rearrangement of the surface charges in the circuit takes place at about the speed of light," and that "the final steady state of the circuit is established in a few nanoseconds," just before they say, "Most lighting actually uses 'alternating current,' in which case the electron sea doesn't drift continuously but merely sloshes back and forth very short distances, everywhere in the circuit, 50 or 60 times per second." Which makes me think that the "final steady state" of my ceiling-light circuit isn't so steady. The surface charges on the wires must be re-arranging themselves continuously, 50 or 60 times a second.

In other words, it appears that the movement of electrons in a wire carrying alternative current involves both constant "re-arrangement" and "flow" like so...

...where the blue dots represent the "surface electrons" that move toward and away from the surface of the wire, and the pink dots represent "current electrons" that move, longitudinally, through the wire.

Now it seems to me we can picture the various arrangements of the blue "surface electrons" in such a circuit as a forming, over time, a kind of three-dimensional sine wave in the wire, pushing the pink "current electrons" back and forth. Like so:

At time 0 we have the wire in equilibrium. The sine wave is at 0, start of a cycle.

At time 1 the blue electrons on the left have made it all the way to the surface, while the blue electrons at the other end of the wire have hardly moved at all. This creates a potential difference that sucks the pink electrons leftward. The sine wave has reached it's positive peak.

At time 2 all the blue electrons have reached the surface. There is no potential difference and the pink electrons have thus stopped moving. The sine wave is again at 0, in the middle of the cycle.

At time 3 the blue electrons on the left have fallen inward while the ones on the right are still on the surface. This creates a potential difference that pushes the pink electrons to the right. The sine wave now reaches it's negative peak.

At time 4 all the blue electrons have fallen back to the initial state, and the pink electrons have again ceased to move. The sine wave is again at 0, end of cycle.

Ya think?

 

[anorlunda]

This article may be helpful

https://en.m.wikipedia.org/wiki/Skin_effect

 

[Baluncore]

Ya think?

You have now discovered the truth. It has clearly come as a bit of a shock.

You now know that an EM wave follows the wire surface.
That the electron disturbance travels on the surface of the conductor at close to the speed of light.
The conductive wires guide the E and M fields that carry energy from the supply to the load.
The direction of the energy transfer is the Poynting vector.
The electric and magnetic fields between the wires carry the energy, not the wire.

 

[Jony130]

In Standard Handbook for Electrical Engineers we read
"The usually accepted view that the conductor current produces the magnetic field surrounding it must be displaced by the more appropriate one that the electromagnetic field surrounding the conductor produces, through a small drain on the energy supply, the current in the conductor.
Although the value of the latter may be used in computing the transmitted energy, one should clearly recognize that physically this current produces only a loss and in no way has a direct part in the phenomenon of power transmission."
http://www.prosoundtraining.com/sit...ng-electricity-means-understanding-the-field/

 

[Gerry Rzeppa]

This article may be helpful https://en.m.wikipedia.org/wiki/Skin_effect

Yes, thank you. More below.

You have now discovered the truth. It has clearly come as a bit of a shock. You now know that an EM wave follows the wire surface. That the electron disturbance travels on the surface of the conductor at close to the speed of light. The conductive wires guide the E and M fields that carry energy from the supply to the load. The direction of the energy transfer is the Poynting vector. The electric and magnetic fields between the wires carry the energy, not the wire.

See below.

In Standard Handbook for Electrical Engineers we read "The usually accepted view that the conductor current produces the magnetic field surrounding it must be displaced by the more appropriate one that the electromagnetic field surrounding the conductor produces, through a small drain on the energy supply, the current in the conductor. Although the value of the latter may be used in computing the transmitted energy, one should clearly recognize that physically this current produces only a loss and in no way has a direct part in the phenomenon of power transmission."
http://www.prosoundtraining.com/sit...ng-electricity-means-understanding-the-field/

The place where Chabay and Sherwood helpfully elaborate on the above statements (and the part that I've personally found enlightening) is where they describe the physical mechanism that causes the various fields that move the "current electrons" through the wire; they describe a physical mechanism that is definitely in (or at least on) the wire (and thus somewhat immune to the particular configuration of the wire, which has concerned me for some time); specifically, they attribute the fields to the non-uniform surplus/deficit of electrons on or near the surface of the wire in various places. In other words, the fields, in the Chabay and Sherwood model, are an effect (of electron re-arrangement) first, and only afterward the cause of further activity (current flow). Three observations:

1. I think the Chabay and Sherwood model is helpful since it answers "troublesome" questions that students often and naturally raise -- questions not typically addressed in standard texts. For example, many students intuitively insist, even when they're told that the current flow on both sides of (and inside) a resistor is the same, that there must still be something different in the wires before and after the resistor; that electrons must, in some way, "pile up" on the one side: and Chabay and Sherwood give them a satisfying answer -- electrons do indeed "pile up" on one side and not the other; there's a significant difference in surface charge on the two sides.

2. The Chabay and Sherwood model is also helpful because it makes it clear that we're dealing with two distinct roles for electrons in a circuit: (a) the electrons involved in the generation of the various fields along the wires (the ones I've colored blue) and, (b) the electrons involved in current flow (the pink ones). I find this distinction helpful because, while the "I" in V=IR has always had a easy-to-understand relationship with electrons (6x10^18 "pinkies" past a point per second), the "V" has only been described using abstract terms like pressure and potential. "V", in the Chabay and Sherwood model, is a much more tangible thing -- a measure directly related to the difference in the number of "blue" electrons on or near the surface of the wires and devices in two places. In short, thanks to Chabay and Sherwood, we can now understand (and picture) both current and voltage in terms of the arrangement/movement of electrons. In an earlier thread I posted this picture, describing what I intuitively thought must be happening in the wires between a guitar pickup and an input resistor:

Turns out that intuitive guess wasn't far off, at least according to Chabay and Sherwood (though the ratio of surface-to-current electrons is a bit exaggerated in the images -- seems it doesn't take many surface charge electrons to move a lot of current electrons). At t1 there really is an excess of electrons on the (surface of) the bottom leg of the circuit, and a corresponding deficit of electrons on the (surface of) the top leg. And at t2 there really is a dearth of electrons on the (surface of) the bottom leg, with a corresponding surplus on the top leg. We thus have a picture that agrees with the words that agrees with the formulas; intuition and reality have kissed.

3. In spite of how helpful the Chabay and Sherwood model is, it in essence only moves the big question back a step. What causes the surface electrons (the blue ones) to behave as they do? How do they "know" to pile up here rather than there? How do they all "get the message" so quickly? Obviously they must interact with each other in some way and/or be operated upon by some outside force. What are those interactions and/or forces at play? Ah, the "scientific method" at work -- with each answer comes more questions!

 

[nsaspook]

I've been doing some bedtime reading in Chabay & Sherwood's Matter & Interactions textbook (https://www.amazon.com/gp/product/0470503475/?tag=pfamazon01-20) and have come across some interesting tidbits. Here they are:

Ya think?

I think you maybe have started accepting information that's been told to you at least a hundred times in the past. If the fog has lifted you can now see now how wonderfully consistent and simple in principle the truth is.

 

[Gerry Rzeppa]

I think you maybe have started accepting information that's been told to you at least a hundred times in the past. If the fog has lifted you can now see now how wonderfully consistent and simple in principle the truth is.

Slow learner, I guess. I thank all who have been patient with me.

 

[anorlunda]

I think your OP misses some key points that are explained in the skin effects article linked above.

The "pink" electrons in the center hardly move at all. It is the electrons at the skin that carry the power current. The approximate electrical model of a solid wire with AC is that of a hollow cylinder.

Distribution of current flow in a cylindrical conductor, shown in cross section. For alternating current, most (63%) of the electric current flows between the surface and the skin depth, δ, which depends on the frequency of the current and the electrical and magnetic properties of the conductor.​

Your analysis based on charge density is seriously deficient because it does not consider the dominant effect, namely eddy current loops.

Skin depth is due to the circulating eddy currents(arising from a changing H field) cancelling the current flow in the center of a conductor and reinforcing it in the skin.​

Skin effect is why power line conductors (and common lamp cords and even cheap USB cables ) are multi-strand. For one thing, a multi-strand bundle has a higher ratio of surface area/mass than does a solid wire. For another, each conducting strand in the bundle carries current, even the ones that pass through the center of the bundle. Some power line conductors have a center core that is selected for tensile strength, not electrical conductivity. The spiral twisting of the strands also aids the electrical properties although I don't remember how. Busbars designed for extremely high currents are actually built as hollow cylinders.

The same reasoning applied when there are multiple conductors per phase in high voltage power transmission lines, 2, 3, and even 4 multi-strand bundles are strung. They are always arranged as if on the perimeter of an imaginary circle. None are routed through the center of the circle. That is illustrated by the spacer below which can arrange 6 conductors in a single phase of a three phase line. The bottom picture shows four conductors per phase. The multiple conductors approximate the electrical characteristics of a large-diameter hollow cylinder which gives less losses than the same mass of strands all wound on a single bundle with a smaller diameter and much better than the same mass as a solid wire.

All this arrangement of strands, bundles, and conductors is designed to minimze the resistive losses of the power line.

Edit: I neglected to say that each strand in a multi-strand bundle has its own skin effect, and that small-diameter eddy-current-loops have less losses than large-diameter loops. The extremely fine strands in a lamp cord bundle have relatively little eddy current losses.

 

[Gerry Rzeppa]

I think your OP misses some key points that are explained in the skin effects article linked above. The "pink" electrons in the center hardly move at all. It is the electrons at the skin that carry the power current.

It appears my previous drawings have been misleading -- the pink electrons are not literally "in the center" of the wires, they are just further in than the blue surface charge electrons that generate the fields that move the pink ones. No doubt the entire "electron sea" is closer to the surface than the center; after all, a copper pipe (with nothing but air in the center) makes a fine conductor.

But according to Chabay and Sherwood, the electrons in this close-to-the-surface sea divide into two groups, each serving a distinct purpose: (a) the members of the blue group positioning themselves, at the speed of light, non-uniformly on the surface of the conductors and thus creating potential differences which in turn create electric fields that move (b) the members of the pink group through the wire at much slower speeds -- also near the surface, no doubt, but further in than the surface charges. Here's a better rendition of my previous image:

The arrows show electron flow, not conventional current. Note that it's the pink electrons that constitute the bulk (if not all) of the current; the blue electrons move mostly (if not only) toward and away from the surface of the wire to create the necessary fields to move the pink ones. Seems to me this is consistent with your illustration of eddy currents above (albeit with a minor change in coloring to separate the two groups, and a slight re-arrangement of the pink arrows to make it clear that they, too, are near the surface):

Better?

 

[anorlunda]

Better?

Better yes, but you still don't acknowledge the circular loops of the eddy currents. Some electrons move opposite to the current flow some of the time.

 

[sophiecentaur]

Better yes, but you still don't acknowledge the circular loops of the eddy currents. Some electrons move opposite to the current flow some of the time.

The movement of electrons is largely random and thermal - more or less 50% 50% forward and backwards. The net movement is a very small proportion of the electrons and that's what constitutes the current that's measured.

 

[Baluncore]

Better?

The magnetic fields are still shown inside the conductor. Only about 1 part in a million is inside the good conductor, the rest of the field is outside with the current flowing in the surface skin.

The surface of a good conductor is a very good mirror to EM fields. The incident magnetic field at the surface induces a current on the surface at right angles. That eddy current again generates a magnetic field at right angles, which is then the opposite direction to the incident wave, 90° + 90° = 180°. They cancel with very little loss, hence the mirror.

But the small amount of current and magnetic field that does penetrate the conductor represent the resistive loss of the conductor. The more resistive the material, the deeper the diffusion into the material and the greater the “resistive losses”.

So any electrons that diffuse into the wire due to imperfect conduction represent loss. Any electrons that remain on the surface represent efficient support for the conduction of energy.

That is a quite different model to the junior guide to electricity, where the current flows in the wire, while the magnetic field radiated represents a loss of energy.
Once you reverse that early concept, you have begun the exciting transition to become an electro-magnetician.

 

[Gerry Rzeppa]

Better yes, but you still don't acknowledge the circular loops of the eddy currents. Some electrons move opposite to the current flow some of the time.

I do acknowledge them. In fact, I'm picturing the blue dots in this diagram...

...moving like the blue arrows in this diagram:

It's just hard to show at the smaller scale. It seems to me that the smaller eddy currents are undesirable and that in the ideal (but, I imagine, impossible-to-achieve) case the blue guys would simply move toward and away from the surface of the wire, as required, and may also follow the path of the larger blue loops (which seems harmless enough, and may even prove beneficial). But in this ideal case they would avoid the smaller blue loops which actually oppose the pink flow of current about half the time.

 

[Gerry Rzeppa]

Any electrons that remain on the surface represent efficient support for the conduction of energy.

Yes, I believe that is what Chabay and Sherwood and I are saying. Non-uniform accumulations of blue surface electrons create the fields that move the pink current electrons that are further (but not very much further) inside the wire.

 

[Baluncore]

In A Simple Circuit, Where Does The Energy Flow?
A Collection of Diagrams

http://amasci.com/elect/poynt/poynt.html

 

[anorlunda]

In A Simple Circuit, Where Does The Energy Flow?
A Collection of Diagrams

http://amasci.com/elect/poynt/poynt.html

Thank you Baluncore. That was very helpful. It helped me expand my horizons. It would make a great PF Insights article.

 

[Gerry Rzeppa]

In A Simple Circuit, Where Does The Energy Flow? A Collection of Diagrams http://amasci.com/elect/poynt/poynt.html

I saw those diagrams when I was first looking into this matter and found them somewhat hard to take at face value. Apparently Chabay and Sherwood had a similar reaction since they begin their discussion with these questions:

Their final answer is that while it is true that the fields in and around the wires move the "current electrons" in a circuit, it is the arrangement of surface electrons that determines the fields, and thus the flow of electricity. As we know from experience, this flow is more-or-less immune to changes in the physical configuration of the wires (at reasonably low frequencies) since the surface electrons automatically re-arrange themselves, at the speed of light, to compensate for layout changes. This, in fact, was the question that puzzled me at the beginning: If the energy in a circuit is carried by the fields, as indicated in a drawing like this...

...then why doesn't a significant change in physical configuration make the bulb more or less bright? Or, as I originally asked, why doesn't the physical configuration of the heater wires in a tube amp, like those variants shown below, have a greater effect on performance?

(The bottom right layout uses the chassis as one of the wires.) Thanks to Chabay and Sherwood, the answer is now clear: the surface electrons arrange themselves differently in each case to automatically compensate, as best they can, for variations in the layout. In short, the surface electrons automatically arrange themselves so that the resulting fields will normalize the flow of current electrons in the circuit.

 

[Baluncore]

It would make a great PF Insights article.

Yes. But it would need to include the deeper skin effect reverse currents that cancel. I have considered it, but best for now is to exercise the ideas in threads like this until we can get a good clean modular framework of understanding.

...then why doesn't a significant change in physical configuration make the bulb more or less bright?

Where the conductors fold back to lessen the distance, the electric field remains the same voltage while the magnetic field of the overlap mostly cancels. That shortens the circuit electromagnetically, in the same way as using shorter wires. It is often forgotten that the voltage drop along the wires is much less than the drop across the load.

Thanks to Chabay and Sherwood, the answer is now clear: the surface electrons arrange themselves differently in each case to automatically compensate, as best they can, for variations in the layout. In short, the surface electrons automatically arrange themselves so that the resulting fields will normalize the flow of current electrons in the circuit.

The external fields create the surface currents as the fields are guided by the surface current formation. The wire is like the hand rail on stairs. As the wave travels, it runs it's hand along the conductor, coordinating the movement of surface electrons in the process. The electron current is a proxy for, and an artefact of, the guided magnetic field.

 

[Gerry Rzeppa]

The external fields create the surface currents as the fields are guided by the surface current formation. The wire is like the hand rail on stairs. As the wave travels, it runs it's hand along the conductor, coordinating the movement of surface electrons in the process. The electron current is a proxy for, and an artefact of, the guided magnetic field.

Okay, but back up one step. What creates the external fields?

 

[Baluncore]

Okay, but back up one step. What creates the external fields?

The return circuit of two wires to the load is actually a parallel transmission line. When you connect the battery the voltage step needs to charge the capacitance of the source end of the T'line. The charge that begins to flow through the source creates the first magnetic field. That voltage step transient flows out and along both the lines toward the load followed by the magnetic field and induced surface current.

It is easy to get into a chicken or egg situation if you look at the wire only. But making the circuit between the voltage source and the transmission line demonstrates clearly that the energy flows out of both the top and bottom of the battery as one EM wave.

 

[Gerry Rzeppa]

The return circuit of two wires to the load is actually a parallel transmission line. When you connect the battery the voltage step needs to charge the capacitance of the source end of the T'line. The charge that begins to flow through the source creates the first magnetic field. That voltage step transient flows out and along both the lines toward the load followed by the magnetic field and induced surface current.

It is easy to get into a chicken or egg situation if you look at the wire only. But making the circuit between the voltage source and the transmission line demonstrates clearly that the energy flows out of both the top and bottom of the battery as one EM wave.

I'm having trouble reconciling your description with this one from Chabay and Sherwood:

1. Your description sounds like the chemically-induced movement of electrons from the positive to the negative end of the battery causes symmetrical fields to emanate simultaneously from both ends of the battery, causing the steady-state surplus of surface charge at location 3, and the steady-state deficit of surface charge at location 4, to form simultaneously -- entirely due to the efficacy of the fields. Bear with me.

2. Their description, on the other hand, has electrons leaving the negative end of the battery and piling up at the entrance to the resistor (because they can't easily get through), and this, in turn, causes a deficit of electrons at the resistor's exit, etc. The steady-state surplus of surface charge at location 3 thus forms first, and the steady-state deficit of surface charge at location 4 thus forms later -- both due to a clockwise flow of electrons through the circuit. Keep bearing.

3. I would intuitively posit that electrons are sucked into the battery from all along the left wire (leaving a deficit at location 4) and are simultaneously shoved into the right wire (causing a surplus at location 3). Which obviously sounds more like the simultaneous effects of the fields/transients/waves that you describe than the clockwise, step-by-step description given by Chabay and Sherwood.

I guess that makes you my new hero. Though I wish you drew pictures. And there is still that chicken-and-egg problem. Is it the sucking and shoving of electrons that gives rise to the fields? or, Is it the fields that induce the sucking and shoving of the electrons? Your description says the chicken, in the beginning, is the movement of electrons: "The charge that begins to flow through the source creates the first magnetic field." But after that it sounds like you've got the fields playing the role of chicken. Help! But be careful you don't fall off your new-found pedestal! :)

 

[nsaspook]

"The charge that begins to flow through the source creates the first magnetic field."
Don't read too much into 'flow' and 'create' as a chicken-and-egg/cause-effect problem. The flow doesn't need to be uniform or continuous in the circuit as a result of the connection transient and the magnetic field is not really 'created' but should be viewed as a transformation of our view of the field as it interacts with the charges in the conductor when they respond to the field. As you can see a step-by-step description of isolated terms easily leads to confusion when the circuit is a system.

 

[Gerry Rzeppa]

"The charge that begins to flow through the source creates the first magnetic field."
Don't read too much into 'flow' and 'create' as a chicken-and-egg/cause-effect problem.

The problem, my friend, is that I'm human: it is natural for me to understand things in terms of cause and effect, in terms of changes in state over time. I have a lot of trouble thinking any other way.

The flow doesn't need to be uniform or continuous in the circuit as a result of the connection transient...

No problem there. A lot of unruly stuff usually attends anything that is starting or stopping.

...and the magnetic field is not really 'created' but should be viewed as a transformation of our view of the field as it interacts with the charges in the conductor when they respond to the field.

I'm sorry, but that sounds like a new-age description of love. Instead of a prosaic, "Love is doing what's best for the other person even when it's not best for you," they say things like, "Love is a transformation of our view of the absolute as it interacts with individuals in the world when they respond to the absolute." :) But seriously, the field must come from somewhere, be caused by something. And though it may quickly get messy (since the field moves electrons which movement causes changes in the field, etc), surely there must be a simple beginning in there somewhere. After that it's just a matter of picking an appropriate level of abstraction so the details (like the movement of individual air molecules in pneumatics) don't distract us from the big picture (pressure is everywhere equal in a cylinder of compressed gas).

As you can see a step-by-step description of isolated terms easily leads to confusion when the circuit is a system.

I fully agree that circuits must be considered as a whole, from "both ends," as it were. Which can be difficult, of course, but which also gives us the opportunity to simplify by focusing on general and overall effects at a higher level of abstraction. Note how simple and straightforward (and yet, I believe, conceptually accurate) my intuitive description of the above circuit is: "...electrons are sucked into the battery from all along the left wire (leaving a deficit at location 4) and are simultaneously shoved into the right wire (causing a surplus at location 3)." The chemical reaction in the battery is the cause -- it sucks at one end and shoves at the other -- and the flow of electrons, resulting in a deficit on one side and a surplus on the other, is the overall effect. The problem, of course, is that both the physicist and the engineer find such a description unsatisfactory. The physicist says I've left out the most important part (the field) and the engineer, thinking in conventional V=IR current terms, cannot bear the thought of electrons being anything but equally distributed in the circuit. It's lonely in the middle of the road.

 

[nsaspook]

But seriously, the field must come from somewhere, be caused by something. And though it may quickly get messy (since the field moves electrons which movement causes changes in the field, etc), surely there must be a simple beginning in there somewhere.

I was saying the magnetic field was not 'created' from the changing electric field because there is really just one electromagnetic field so it (magnetic field) didn't just pop out of nothing simply because an electron moved. The transformation of the properties of EM energy is something we take for granted because it's so common. The power used in your computer has been transformed many times by shifting the ratio of voltage (electric) to current (magnetic) for the same amount of power flowing from a power station to the electrical connection its plugged into.

It turns out that any inertial frame will do. We will also see that magnetism and electricity are not independent things—that they should always be taken together as one complete electromagnetic field. Although in the static case Maxwell’s equations separate into two distinct pairs, one pair for electricity and one pair for magnetism, with no apparent connection between the two fields, nevertheless, in nature itself there is a very intimate relationship between them that arises from the principle of relativity. Historically, the principle of relativity was discovered after Maxwell’s equations. It was, in fact, the study of electricity and magnetism which led ultimately to Einstein’s discovery of his principle of relativity. But let’s see what our knowledge of relativity would tell us about magnetic forces if we assume that the relativity principle is applicable—as it is—to electromagnetism.
...
Since electric and magnetic fields appear in different mixtures if we change our frame of reference, we must be careful about how we look at the fields

and

. For instance, if we think of “lines” of

or

, we must not attach too much reality to them. The lines may disappear if we try to observe them from a different coordinate system. For example, in system

there are electric field lines, which we do not find “moving past us with velocity

in system

.” In system

there are no electric field lines at all! Therefore it makes no sense to say something like: When I move a magnet, it takes its field with it, so the lines of

are also moved. There is no way to make sense, in general, out of the idea of “the speed of a moving field line.”

http://www.feynmanlectures.caltech.edu/II_13.html

 

[Baluncore]

No problem there. A lot of unruly stuff usually attends anything that is starting or stopping.

It is the close study of the start and/or stop that identifies the mechanism. The steady state hides the phase information. We live in a universe of incompatible interfaces. It is not the bulk properties or the steady state that is important, it is the transition or the transient that is the key.

I fully agree that circuits must be considered as a whole, from "both ends," as it were.

No. "Both ends" are effectively isolated by the crude transmission lines between them. A transient travels the "scattering matrix" of the circuit, it knows not where it will go or how much will be later reflected.

 

[Baluncore]

Refractive Index is a Ratio.
The ratio of EM wave speed in space to the EM wave speed in a conductive material is the refractive index of that material. We know that copper is highly reflective to EM waves, with a Refractive Index of about 1 million at 1 MHz. A 1 MHz EM wave has a velocity of only about 400 metres per second in copper.
An EM wave incident on a good conductor in space will induce a surface current as the EM wave is reflected by the conductor. In that case it is clear that the magnetic component of the EM wave induces the momentary current in the surface of the conductor. We can therefore see that the EM wave travels over the conductive surface, guided by the local disturbance of surface charges.

Transmission lines are everywhere.
The transmission line concept is based on a conceptual low pass filter made from distributed series inductance and parallel capacitance. The velocity of a wave on a transmission line is close to the speed of light, it is determined by the magnetic and electric properties of the material outside the conductor. Every wire or conductive surface we use is a transmission line in it's environment.

Trains of traveling surface disturbance can travel in opposite directions on the same lines.
There can be many pulses or cycles of RF on a transmission line at the same time. All are propagating at the velocity factor of the cable. Waves can be traveling in both directions and pass without interference. That must be due to the EM wave guided by the conductor surface, not by the electron current in the conductor.

Energy Flows as Fields.
The speed of energy flow is the same as the speed of the EM disturbance on the transmission line. The three orthogonal vectors are the Electric, Magnetic and the Poynting vector which shows the direction of energy flow.

A Conceptual Bulkhead.
In junior science we have current on conductors and voltage between conductors.
In senior physics we have E, M and Poynting energy flow in the space between conductors.
Where we draw the line between the consistent conceptual domains has now become obvious.

We avoid translation between the conceptual domains by recognising that:
The voltage between two conductors can be measured, it is a proxy for the electric field strength.
The current on a wire can be measured, it is a proxy for the magnetic field strength.
The product of V and I is power, just as the product of E and M is the poynting vector of energy flow.

In the junior science model we see a return circuit where a current flows out of one end of the battery, along the wire, down through the load and back through the return wire to the other terminal of the battery.
With the senior physics model we see a wave travel from the source towards the load. It travels as a differential wave on the two parallel wires, away from the battery, until it reaches the load. There is no later “return current path” concept needed.

The junior science model is sufficient to interest a student and to train an electrician or technician.
The senior physics model is necessary to predict and explain the details of the reality we observe.

 

[Baluncore]

The Origin of the Skin Effect.
As the guided surface wave caresses the surface electrons, a very small component of EM field diffuses into the conductor. The velocity of that diffusion is very slow. In copper, at 1MHz it is about 400 m/sec, at 60Hz it is only 3.2 m/sec. If you could do a rapid archaeological dig into the surface of an AC conductor, you would start with current flowing one way at the surface, then below that would be an older remnant reverse current from half a cycle earlier. The reversals continue with depth. That sequential historical sinewave is exponentially attenuated with depth by the diffusion process. All the internal alternating currents deeper, or older, than about half a cycle cancel in their effect. Only the surface current for this half wave is really important externally. The thickness of that layer is called the skin depth. It explains why only the surface of a conductor is important at high frequencies.

 

[anorlunda]

The junior science model is sufficient to interest a student and to train an electrician or technician.
The senior physics model is necessary to predict and explain the details of the reality we observe.

You could have mentioned that there is a third level, quantum electrodynamics, for a still deeper view of reality.

 

[Gerry Rzeppa]

In the junior science model we see a return circuit where a current flows out of one end of the battery, along the wire, down through the load and back through the return wire to the other terminal of the battery.

With the senior physics model we see a wave travel from the source towards the load. It travels as a differential wave on the two parallel wires, away from the battery, until it reaches the load. There is no later “return current path” concept needed.

Sorry, guys, but I need an example. Let's take these three circuits:

The junior model says that in all three, a chemical reaction in the battery causes electrons to be simultaneously sucked from the red wire (into the battery) and shoved into the blue wire (from the battery). This causes a deficit of surface electrons in the red wire, and a corresponding surplus of surface electrons in the blue wire -- and this difference in surface charge accounts for the potential difference, or voltage, that we observe (with our voltmeter) between the wires and across the bulb. The uniform flow of other electrons through the entire circuit (that we can measure with an ammeter) is called current. The bulb glows because current electrons, flowing through the highly-resistant filament of the bulb, collide with obstructions, heat up the filament, and release energy in the form of photons.

How would you describe the operation of these circuits with the senior model in mind? Be sure to include an explanation of how and why the "differential wave" manages to impart virtually the same amount of energy to the load whether the wires are parallel, goofed up, or the bulb is turned 90 degrees from it's former orientation.

 

[Baluncore]

How would you describe the operation of these circuits with the senior model in mind? Be sure to include an explanation of how and why the "differential wave" manages to impart virtually the same amount of energy to the load whether the wires are parallel, goofed up, or the bulb is turned 90 degrees from it's former orientation.

I see no reason why the understanding must be made more difficult by scrambling the 3D field geometry. The Senior Physics Model needs the understanding of a Physicist, so let's start at the beginning.

1. Do you understand how a transmission line works as distributed series inductance with distributed parallel capacitance ?
2. Can you calculate the velocity factor of that transmission line ?
3. Can you calculate the characteristic impedance of that transmission line ?
4. Do you understand why the reflection coefficient is important where two lines with different impedance meet ?

 

[Gerry Rzeppa]

I think somebody's pedestal is teetering...

I see no reason why the understanding must be made more difficult by scrambling the 3D field geometry.

Chabay and Sherwood are able to describe their model, using the three circuits above as examples, in terms accessible to introductory-level physics students. I was hoping you'd be able to do the same with your "senior model" so I could compare and contrast the two.

1. Do you understand how a transmission line works as distributed series inductance with distributed parallel capacitance ?

Yes, I get the general idea, assuming the general idea is encapsulated here: https://en.wikipedia.org/wiki/Distributed_element_model

2. Can you calculate the velocity factor of that transmission line ?

Sure. We just plug the numbers into the formula found here: https://en.wikipedia.org/wiki/Velocity_factor

3. Can you calculate the characteristic impedance of that transmission line ?

Yes, again. This time we do the plugging into the formula found here: https://en.wikipedia.org/wiki/Characteristic_impedance

4. Do you understand why the reflection coefficient is important where two lines with different impedance meet ?

Yes. There's a readable description here: https://en.wikipedia.org/wiki/Reflection_coefficient

But most of that, I believe, is beside the point. When I read Chabay and Sherwood I skip most of the math; it's their qualitative descriptions that interest and inform me. I was hoping, as I said above, that you'd have a similar qualitative description of your senior model for me to chew on. A "Senior Model for Dummies" kind of thing. After all, "The real genius is the guy who can explain, to the average man, what the other genii are saying." Was I wrong in thinking you were such a one?

 

[Baluncore]

I think somebody's pedestal is teetering...

After all, "The real genius is the guy who can explain, to the average man, what the other genii are saying." Was I wrong in thinking you were such a one?

Yes. If you put me on a pedestal it casts more doubt on your judgement than my ability. I suffer from vertigo, so I am scared of heights, and my wheelchair brakes don't work.

Are you talking about a stable direct current, an AC sinewave or a step transient ?

 

[Gerry Rzeppa]

Are you talking about a stable direct current, an AC sinewave or a step transient ?

I'm asking how the functioning of these three circuits might be described in a "Senior Model for Dummies" text, both (a) when the battery is first connected, and (b) after a steady state is reached. What happens in and around the battery, the wires, and the bulb that makes it light up?

 

[sophiecentaur]

"Senior Model for Dummies"

Isn't this just an oxymoron?
The Senior model contains a lot of well established maths and empirical evidence (doesn't it?). How can this be for dummies?
Gerry: your model contains just pictures and a main reference that contains very little Maths (iirc). What do you actually want out of this exercise? Companions in your escape plan? To reject the present models and move to another one, surely you are duty bound to get to know the present models at a very high level.
You answered Baluncolre's four questions with references to Wiki. Does that imply that you are familiar with it all or that your search has revealed a possible source of the information? And Wiki can be shaky sometimes.

The real genius is the guy who can explain, to the average man, what the other genii are saying.

That statement is not really much more than a soundbite. Some genii can pass some of their learning on at a low level but (and it has happened to me on several occasions) being told something by a genius, it is possible to leave, thinking you now understand it all - but you couldn't repeat what you have learned or use it to synthesise anything further. Charisma and genuis sometimes go together but . . . . . .

 

[nsaspook]

I'm asking how the functioning of these three circuits might be described in a "Senior Model for Dummies" text, both (a) when the battery is first connected, and (b) after a steady state is reached. What happens in and around the battery, the wires, and the bulb that makes it light up?

View attachment 89684

I think you have a pretty good idea what happens and are starting to fall off the wagon again.