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"Veritasium" (YT) - "The Big Misconception About Electricity" ?

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bdunham7:

--- Quote from: EEVblog on January 01, 2022, 04:06:28 am ---But once again for me it comes down to the DC question (and also low frequency AC like 50/60Hz power transmission). Does the energy *actually* flow in the field or not. My engineer mind is vastly more at ease with the quantum field theory and it's implication at DC and LF. I'd only take power flowing in the field (and hence dielectrics like PCB material and coax cable material) at really high frequencies. It just doesn't "feel right" that the energy is flowing in the field at DC."

--- End quote ---

So if I have a long, slow transmission line--like a really effective delay line--I can put a pulse of energy in and then I can understand that the energy is in that pulse, a wave travelling through the transmission line, although charges are still moving.  Same if a pulse is radiated through an EM wave, you can understand that the energy is travelling through space, in the form of a wave/photon.  But in those cases you have changing fields and you can point to the energy as it moves and say "there it is!" at each point in it's travels.  In the DC case, I don't see how you can say that as the only thing moving are the charges--the fields are static and conservative.  And for the LF case like power distribution, perhaps it is a blend, but the question is which model dominates?  Can you point to the 'energy' and say "there it is!" at each point in time?  I think you absolutely can--and you'll be pointing at the charges. The fact that you can calculate an S-field and Poynting's Theorem still works out mathematically does not persuade me of anything in particular here. 

bdunham7:
So here's a thought experiment.  I'm going to invent some tools called 'Millikan tongs' that allow me to grasp and hold a single electron and move it around.  They are weightless and perfectly insulated, so the only effort I need to exert is the work required to move the electron from one point to another. 

What I'm going to do is take the DC power circuit and separate the electric field from the conduction of the charges.  I have a large ground plane, then another plane 1 meter above it.  I then have a battery (the source) that charges the upper plane to -1V relative to ground, which means there is an electric field of 1V/m between the planes.  I then install a wire with a resistor in the middle (the load)  so that it goes almost all the way up to the upper plane, but not quite, so the circuit is not complete.

Now, if I take my Millikan tongs and pluck an electron from the battery side, right near the top so that it is very near the -1V potential and then move the tongs to the top of the load wire, this will require zero work because I am moving it perpendicularly to the E-field lines--IOW it's potential energy is not changing.  When I get there and release the electron, it will cause a current through the load, releasing a certain amount of energy.  So how much energy and can we point to it as it flows?  In this case, for each electron I do this for, there will be 1eV of energy released into the load.  And each electron has a potential energy in the field of 1eV, so as the electrons are moved by the tongs, I can point to it and say "there it is!--there's my 1eV of energy!"  The E-field itself is static and conservative.  If I use the tongs to pick up an electron from the ground side, I will have to do 1eV work to get it up to the top, but at each stage I can point to it and say "there is xxx amount of energy!".  So in this special case, can we agree that the energy is 'flowing' in the succession of 1eV-potential electrons being carried by the tongs?  It's hard for me to see it any other way.

EEVblog:

--- Quote from: bdunham7 on January 01, 2022, 04:31:28 am ---
--- Quote from: EEVblog on January 01, 2022, 04:06:28 am ---But once again for me it comes down to the DC question (and also low frequency AC like 50/60Hz power transmission). Does the energy *actually* flow in the field or not. My engineer mind is vastly more at ease with the quantum field theory and it's implication at DC and LF. I'd only take power flowing in the field (and hence dielectrics like PCB material and coax cable material) at really high frequencies. It just doesn't "feel right" that the energy is flowing in the field at DC."

--- End quote ---

So if I have a long, slow transmission line--like a really effective delay line--I can put a pulse of energy in and then I can understand that the energy is in that pulse, a wave travelling through the transmission line, although charges are still moving.  Same if a pulse is radiated through an EM wave, you can understand that the energy is travelling through space, in the form of a wave/photon.  But in those cases you have changing fields and you can point to the energy as it moves and say "there it is!" at each point in it's travels.  In the DC case, I don't see how you can say that as the only thing moving are the charges--the fields are static and conservative.  And for the LF case like power distribution, perhaps it is a blend, but the question is which model dominates?  Can you point to the 'energy' and say "there it is!" at each point in time?  I think you absolutely can--and you'll be pointing at the charges. The fact that you can calculate an S-field and Poynting's Theorem still works out mathematically does not persuade me of anything in particular here.

--- End quote ---

Same here, I have not heard a compelling case of Poynting at DC that makes me think in any way that it's useful.

Sredni:

--- Quote from: EEVblog on January 01, 2022, 05:11:42 am ---I have not heard a compelling case of Poynting at DC that makes me think in any way that it's useful.

--- End quote ---

Take your pick:

Ian M. Sefton
Understanding Electricity and Circuits: What the Text Books Don’t Tell You
(School of Physics, The University of Sydney)
Science Teachers’ Workshop 2002

Mark Heald

    Electric fields and charges in elementary circuits
    American Journal of Physics, 52 (6), June 1984

    Energy Flow in Circuits with Faraday EMF
    American Journal of Physics, 56 (6), June 1988

Manoj K. Harbola
Energy flow from a battery to other circuit elements: Role of surface charges
2010 American Association of Physics Teachers.
DOI: 10.1119/1.3456567

Igal Galilia and Elisabetta Goihbarg
Energy transfer in electrical circuits: A qualitative account
Am. J. Phys. 73 (2), February 2005
DOI: 10.1119/1.1819932

John D. Jackson
Surface charges on circuit wires and resistors play three different roles
American Journal of Physics 64 (7), July 1996

Noah A. Morris, Daniel F. Styery
Visualizing Poynting vector energy flow in electric circuits
American Journal of Physics 80 (6) June 2012, pages 552-554


Let's not forget Sommerfeld:

Sommerfeld
Lectures on Theoretical Physics (6 Volumes)
Academic Press
the third volume about Electrodynamics
p. 125, Detailed treatment of the field of a straight wire and a coil
There you will find an exercise about an infinitely long resistive wire. Back in 1942 the role of surface charge and the direction of Poynting vector for a DC circuits was no mystery at all. Keep in mind that Sommerfeld is considering a very long resistor, but I copy here the conclusion:

https://i.postimg.cc/pV3mnZKp/screenshot-12.png

Or, if you want to fly a bit lower, Kraus

John D. Kraus
Electromagnetics 2e
section 10.20 Circuit Applications of the Poynting Vector
p. 416
on p. 418, after considering a circuit with a battery (DC) and a resistors he writes:

--- Quote ---"In Fig. 10-19aflow lines of the Poynting vector (power flow lines) are shown. It is evident that the power flow is through the empty space surrounding the circuit, the conductors of the circuit acting as guiding elements. From the circuit point of view we usually think of the power as flowing through the wires but this is an oversimplification and does not represent the actual situation."
--- End quote ---

EEVblog:

--- Quote from: Sredni on January 01, 2022, 09:09:39 am ---
--- Quote from: EEVblog on January 01, 2022, 05:11:42 am ---I have not heard a compelling case of Poynting at DC that makes me think in any way that it's useful.

--- End quote ---

Take your pick:

*snip*

John D. Kraus
Electromagnetics 2e
section 10.20 Circuit Applications of the Poynting Vector
p. 416
on p. 418, after considering a circuit with a battery (DC) and a resistors he writes:

--- Quote ---"In Fig. 10-19aflow lines of the Poynting vector (power flow lines) are shown. It is evident that the power flow is through the empty space surrounding the circuit, the conductors of the circuit acting as guiding elements. From the circuit point of view we usually think of the power as flowing through the wires but this is an oversimplification and does not represent the actual situation."
--- End quote ---

--- End quote ---

Nope, still not telling me anything useful, just stating that's a way to look at it.
What can looking at it that way DO FOR ME?

Do you have any comment on how quantum field theory views this? or do you think it's bunk?

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