General > General Technical Chat
"Veritasium" (YT) - "The Big Misconception About Electricity" ?
adx:
--- Quote from: Sredni on January 12, 2022, 03:16:25 pm ---See for yourself
https://aapt.scitation.org/doi/abs/10.1119/1.1286115
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--- Quote from: snarkysparky on January 12, 2022, 05:17:27 pm ---Surface charge accounts for the Electric field intensity at a conducting boundary.
https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electro-Optics/Book%3A_Electromagnetics_I_(Ellingson)/05%3A_Electrostatics/5.18%3A__Boundary_Conditions_on_the_Electric_Flux_Density_(D)
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Well that was quick, thanks for the references (no access the first, but first hit of search pdf of Ellingson answered it straight away).
--- Quote from: Electromagnetics_Vol1.pdf (Ellingson) ---We conclude this section with a warning. Even
though the SI units for D are C/m2, D describes an
electric field and not a surface charge density. It is
certainly true that one may describe the amount of
charge distributed over a surface using units of C/m2.
However, D is not necessarily a description of actual
charge, and there is no implication that the source of
the electric field is a distribution of surface charge.
On the other hand, it is true that D can be interpreted
as an equivalent surface charge density that would
give rise to the observed electric field, and in some
cases, this equivalent charge density turns out to be
the actual charge density.
--- End quote ---
(I assume that last bit relates to electrostatic type charge carried on the surface on insulators.) It's just that a lot of references refer to surface charge as though it's obviously physical, without comment on the reasoning.
Sredni:
Well, surface charge is exceedingly small in ordinary circuits. I have always wondered if there are instances where it would be required to have fraction of the charge of the electron, and how - if it is possible - to resolve that classically
The fields have been shown to be real. See for example jefimenko's 1962 paper ( or his book)
EEVblog:
I've been gone for several weeks, can someone TLDR me what happened here in regards to the quantum field theory explanation? Thanks.
EEVblog:
(after two weeks away I've just jumped back to random page, so I have no idea about any follow-ups to this post)
--- Quote from: bsfeechannel on January 03, 2022, 02:10:28 am ---
--- Quote from: adx on January 03, 2022, 01:33:42 am ---Yet, like it or not, QFT has provided a 'worldview' which assists in 'debunking' (intentionally being loose with that wording) Poynting's vector as a source of truth for power flow at DC, a situation which is not far off being untestestable. It would require the experimental capabilities of Henry Cavendish's Earth density determination squared.
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Debunking? You got to be kidding me. QFT in fact confirms the Poynting vector at DC or at any frequency. The idea that nothing is happening at DC so the energy cannot flow through the fields is a misconception.
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Not according to the quantum professor. Are you catagorically saying she's wrong and that no energy flows inside the wire?
--- Quote ---At DC, AC, whatever, the electrons are exchanging virtual particles. That's why energy flows in the fields, even if the fields are not changing or moving.
--- End quote ---
What if those fields are inside the copper wire at DC?
Again, the fundamental question here is whether energy flows inside or outside the wire (or both). And it should be easiest to argue this for DC.
--- Quote ---Dave thinks that the Poynting vector does not work at DC because he is a circuit-headed engineer. The only way he can think of the energy traveling through space is when you have AC or RF. At DC no worky, because capacitors, transformers, and antennas, which are the only devices he knows that allow the transmission of energy through space, block DC.
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I have never said that Poynting vector math doesn't work at DC, I have in fact said that it does. What I was getting at is that they basically become of no practical relevance at DC.
adx:
--- Quote from: Sredni on January 13, 2022, 01:23:05 am ---Well, surface charge is exceedingly small in ordinary circuits. I have always wondered if there are instances where it would be required to have fraction of the charge of the electron, and how - if it is possible - to resolve that classically
The fields have been shown to be real. See for example jefimenko's 1962 paper ( or his book)
--- End quote ---
I've also wondered about what a few electrons do to picovolt levels. I guess for the "balls in pipe" model, especially if they are 'hot', they can be part in the volume of interest. Only if cut off from the rest of the circuit would it become an electron counter (like a pixel in a CCD, or any high impedance node). I then start wondering about a nanostructure to fit 3 electrons side by side, to reduce the 'cogging' as they go past the metal ions, a 3 phase power delivery nano-system. Even pairs (2 phase). But only if very cold... Oh the blissful ignorance of only ever doing high school level physics. And I digress once (probably an underestimate) more. In any case, I assume the surface charge will quantize to fractions of an electron, because it represents charge inside a surface rather than on it. I had been wondering if a million volts is put across a gap in a vacuum (just under the field emission limit) what will happen - would there be a (numeric) point too many electrons crammed into a monolayer on the surface, if surface charge were physically real? And what would that do to the local field?!
The seeds "strewn" on the circuit are neat. But it feeds into my schooled confusion - in reality there are no field lines etc. It's just the seeds lining up to create circuits of their own across the voltage difference (which is what an electric field is, admittedly), but as a high school student it is (or was for me) hard to know what is meant, especially if some teachers aren't really sure themselves. The field doesn't exist as an infinite continuum on its own, but is simply the sum of field emanating from every charged particle. Not even that - it is the combined interaction force between those particles, the field is an imaginary construct to represent those. I used to sort of wonder how a vacuum can have voltage at a point or between two points. Of course it doesn't - voltage is a property of matter, and is the excess charge density (number of extra or missing electrons from a state of absolute neutrality). When a metal, it represents the mechanical pressure of those electrons in the wire, a pressure that can't exist in a vacuum (unless a cleaner). But the mathematical field can - it predicts the force that would act on a charge if one were there.
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