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

--- Quote from: bsfeechannel on January 01, 2022, 07:45:18 pm ---
I like your video very much, especially that part where you say that, in QFT, there's no distinction between particles and fields. But I have a question. What if your wire, besides the interacting electrons you showed, also had protons?


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Taking account of the protons in the wire would make the model harder to work out and add a correction to the math but it would not change the fundamental semi-classical result.  That the probability of one field interacting with the other would be approximated by the inverse square law.  With a much greater probability of interaction the closer they are (at inter atomic distances) than at a meter apart. 

Treating the wire as a sea of free electrons loosely bound to essentially stationary atoms is the standard way that physicists handel conductors or semi conductors.  This works for a lot of reasons.  Assuming that the energy applied and the temperatrues achieved are not enough to rip apart the atoms the protons should not move much at all.  At most they'd vibrate around equilibrium a little bit and that would introduce a small perturbation to the calculation. 

In short outside of a proton accelerator we don't have to worry about a current of protons.

Now in a semi conductor there can be a current of positively charged holes. Absences of electrons which move like electrons inside the semi conductor. Then there are high energy physics experiments involving positrons ...   As you can see things go way beyond the scope of this problem.  For the purpose of this problem one can ignore the protons.


--- Quote from: bsfeechannel on January 01, 2022, 07:45:18 pm ---Cool, so the energy-carrying particles are the photons, which are just oscillations in the EM field.

--- End quote ---

In the QFT way of thinking about this there is no larger EM field.  What we measure as an EM fields are just coherent states of large numbers of photons.  The fields in Quantum Electro Dynamics are the electron (and it's anti particle) and the photon (which is its own anti particle).  When the right limits are taken we recover the classical description :)





--- Quote from: Sredni on January 02, 2022, 04:44:24 am ---
--- Quote from: EEVblog on January 01, 2022, 01:04:53 pm ---I am not talking about the measurements, they will be as they always have been. I'm talking about the the title of this thread "The Big Misconception About Electricity". Does the energy flow in the field around the wire or does it flow in the wire at DC? Poynting/classical field theory says outside, QFT appears to say inside.
I want to know what you and others who have been so (not incorrectly) dogged about anyone that dares think of this in any other way than Maxwell/Poynting think about this apparent conundrum.

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What I'm saying is that I am not at all sure that the QFT theory pointo of view is at odds with what is forecasted by Poynting. It might make it harder to see, but if you get the same measurements for the fields, then chances are that energy flow will follow what Poynting forecasts.

Regarding that video on QFT, it seems to me the point made is that the conductors are best at 'communicating' the electric field. And I can see that in classical theory as well: if there is only the battery, the electric field of each pole dies off as 1/r^2, and whatever field was there near the poles of your 12V battery, will be greatly attenuated at the distance of 1 meter. But if you attach cables at the two poles and place the other ends near each other (let's say the same distance as the battery's electrodes) one meter away from the battery, you will basically see there the same field you see between the electrodes.
Now, if QFT explains this through probabilities of interactions, instead of fields propagating from charges, well, good for QFT. But does this tell us where the energy actually flows in the first few nanoseconds in Derek's experiment?
In a post above the author of the video says

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It's not "at odds" with it.  All QFT predicts is that while energy can flow via the path Pyonting predicts it can also flow via an Infinite number of other paths.  Incuding paths via the wire.  When one carries out the computation, taking account the presence of existence of the wire as a path of charges which are very close toegher for the battery to interact with, the path of highest probability is along the wire.  The path suggested by Pyonting also exist but the probability of conduction via that path is low. 

The classical theory is not "wrong" it is just too limited for this situation.  The very size of it makes the speed of light relevant and so relativity has to be accounted for.

One could even leave out the QFT aspect of this and analyze the problem using classical relativistic E and M.  What does the E and M field Tensor do in this situation?  Does the Pyonting vector, a cross product, even still make sense in 4d Space time?  In that space time instead of a Pyonting vector we get the E and M stress energy tensor. The pyonting vector is just one part of that. 

Such is why I wanted to just skip all of those intermediate levels and go for the most fundamental theory we have that deals with electricity and magnetism.  The experiment carried out in one of the other videos (the one where someone actually really did the set up with 1 KM of wire) more or less proved it right.  You get a TINY current right away (because there is a low probability path for that energy to travel, predicted by QFT and compatible with the pyonting vector.  Then after the right amount of time passes the higher probaility path, via the wire, the path of least reisistance if you will, the energy arrives at the bulb.

It was a trip that for about two weeks if one googled "Veritasium is wrong" a quote from my blog was the snippet of text that Google put up there. Now that is POWER. 

IT felt like 
https://youtu.be/W8lr7II3dwQ?
adx:
I know it's not, but this sounds very simple in its answer that energy flows mostly in the wires.

I think I see where this comes from now: Those of us in classical land have been struggling with what energy "is", arguing over what voltage and current is and how it translates into energy or power. But for QFT, energy is the fundamental quantity, so it's hard to argue against a statement that it flows via the path of least (mathematical) resistance. Very direct result.

I still have some internal concern that QED relativistic EM deals with potential energies (pressure) rather than real power flow, but that's probably not relevant to this discussion, and I don't even know where to begin on QFT itself.

If I want to go further I'm going to have to get my feet wet with the mathematics, which I never really liked the idea of. I'm fine with numerical simulation (in Excel - only joking, use BASIC  :)).
daqq:
COMSOL jumps into the fray:

https://www.comsol.com/blogs/how-long-does-it-take-an-engineer-to-turn-on-a-light-bulb/?utm_content=bufferc79f7&utm_medium=Social&utm_source=LinkedIn&utm_campaign=comsol_social_pages

Simulation video included.
SandyCox:


Quote from: daqq on Today at 09:29:34 am
COMSOL jumps into the fray:

https://www.comsol.com/blogs/how-long-does-it-take-an-engineer-to-turn-on-a-light-bulb/?utm_content=bufferc79f7&utm_medium=Social&utm_source=LinkedIn&utm_campaign=comsol_social_pages

Simulation video included.

--- End quote ---



The blue line is a comparison of COMSOL's result with transmission line theory.

Note that the blue line is not a simulation. It comes straight from the theory.
 comsol.png (21.94 kB. 974x493 - viewed 244 times.)
Sredni:
Can you zoom in in the first ten nanoseconds, to see how well they match?
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