General > General Technical Chat
"Veritasium" (YT) - "The Big Misconception About Electricity" ?
bdunham7:
--- Quote from: SiliconWizard on January 02, 2022, 02:37:31 am ---It's only been observed for very small particles (notwithstanding the mentioned recent experiments, which are interesting, but for which I'm still prudent.) And as I said earlier, any theory that can't survive observation under certain conditions can't be claimed to be valid for those conditions. So, while many physicists believe that the same laws hold at any scale, the honest ones will tell you that they just don't know. That it appears plausible, but we have no proof. The others are believers.
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OK, I see our point of departure is at the definition of 'failure' of a theory. So you are saying that if the theory is not feasibly falsifiable, we should remain skeptical. It is not currently possible to experimentally verify the de Broglie wavelength of a tuna swimming in the sea, so your position is that we should regard any theoretical statement of it as unproven. That's not an inherently unreasonable position, but keep in mind that it then also applies to common laws that we accept will apply universally, or at least over a broad set of conditions that we don't expect to be able to analyze experimentally. I don't see QM/QED as being any different than any other physical laws or models in that regard. It is verifiable until you simply reach experimental limits. It's not like string theory, which AFAIK has not made any experimentally falsifiable conclusions.
bdunham7:
--- Quote from: SilverSolder on January 02, 2022, 03:02:38 am ---Arguably, you are storing potential energy while moving the magnets closer? - and when they are standing still... that energy is still there!
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If the magnets are aligned so as to attract, it takes negative energy to move them into position from any further position or as physics teachers would posit, from infinity.
Sredni:
--- 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
--- Quote ---"For the phenomena under discussion here Quantum Electro Dynamics would find that the path of highest probability is along the wire, where all the free electrons are and can interact with each other at inter atomic distances VS the vast 1m void between them and the bulb."
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Well, but does this prevent the electric field from the battery from being measured at 1 meter from the electrodes before the interaction between electrons in the wires have made its round trip to the moon and back? I don't think so. You just see a far weaker field than what is allowed by the wires. And this is also what is expected by classical ED. After all, there is a reason why we use cables to power our homes and not big tesla coils...
It's far more efficient to influence the surface charge responsible for the internal electric field in the load by using the interaction between adjacent electrons in the wire, that it is by changing their configuration at a distance. Of course when the wires makes a longer trip than line of sight, we will have to wait a bit more for that far more efficient interaction to reach our load.
Regarding your other point about switching theories
--- Quote ---"You don't need to go as far as Poynting to muddy the waters. Even plain Poynting Thereom can make things so complicated that you won't be able to have intuitive insights."
You are now saying the same thing that many people say about Poynting/Maxwell for DC and LF.
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I can hardly see a parallel, here. Applying Poynting's theorem does not even represent a shift in paradigm. It's 'just' a cross product away from what you must already know in classical theory: i.e. what are the electric and magnetic field in your system. If would not consider it to be so complicated that it will prevent you from having intuitive insight. In my mind it's quite the opposite: it gives you insight on how the energy flows. But of course, YMMV.
Going quantum, on the other hand, changes everything. Current as movement of charge? Nah, there's no such thing as classical trajectory. You might want to consider probability amplitude wave packets in a periodic potential (free electrons? quasi-free? tightly bound? Pick your poison). Try to gain some insight by considering the momentum redistribution in the k-w space. If you're lucky you can try to picture a Fermi sphere in your head and what an electric field would do to that. Joule heating by collisions with the lattice? Forget about that! It's electron-phonon scattering and it's all about imperfections and impurities and the probability of transitions. And don't even think of turning on a magnetic field! You will start to see orbits on Fermi surfaces!!! (yes, I'm taking a few liberties here.)
Nah, I don't think Poynting theorem has any mud in it. Nonclassical ED - even the semiclassical one, on the other hand, is a never ending bog of mud and quicksand.
adx:
Bit late but better post before it gets later...
--- Quote from: bsfeechannel on December 29, 2021, 08:52:09 pm ---If engineers are so dumb these days as you say, why do they get into discussing things they not only do not understand, but, worse, also don't want to understand?
Oh! Of course! They're dumb.
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Maybe the average IQ of engineers is dropping as governments worldwide seem desperate to pump up careers in "ICT"? But I'd be more worried about the increasing proportion for whom it is really not their calling, rather than some synthetic measure of imbued stupid. And it would be a terrible generalisation to apply to individuals. There's differences between not being able to understand, not wanting to understand, not having the time, having other academic priorities etc.
Re-bringing up my comparison to medicine, few doctors are going to remember or use details of molecular biology or anatomy, which is arguably as fundamental and unchanging as classical EM theory. They might still want to discuss things from their training, over a few beers, while performing an easy surgery (oops not that last bit). These won't be 'teaching quality discussions'.
--- Quote from: bsfeechannel on December 29, 2021, 08:52:09 pm ---
--- Quote from: adx on December 28, 2021, 02:31:36 pm ---That's just belief at work. The dubiously existent backfire effect. Maxwellians have been equally triggered by comments which go against their worldview.
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Have you heard of an Einsteinian? If someone calls your attention to the fact that you might be making mistakes because you don't really understand the theory of relativity, you call this person an Einsteinian?
There's no such thing as a "Maxwellian". Maxwell's equations are the theory of everything classical electromagnetism. Everything that is classically electric/magnetic has to be checked against this theory and, if it fails, dismissed right away.
So Maxwell's equations are not a worldview, they are a theoretical tenet of our trade. That's why people get impatient when someone exhibits total ignorance of that fact and claims to be an electronics engineer at the same time. That's cringe worthy and embarrassing.
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The word is "relativists" (or similar). They were considered 'alternative' - not so much because of any belief Einstein was wrong, but the establishment thought his theories of no great significance, or not worth upsetting the apple cart over. I can also use the term if I believe he was not wrong, but missing something. So yes, "relativist", or colloquially, "Einsteinian".
If it's not a worldview, and just a theory, then I can take it or leave it, without fear of others' impatience, cringe or referred embarrassment. There is something quite inconsistent with your argument.
Or I can accept it is beyond me, and by your argument that circuit theory etc is a subset of his theory, then rely on these tools.
Or I can look on it as fondly as I like, but reject the mathematics as intractable and unpleasant to my tastes.
And it really is intractable and not far off useless in the real world. The people pushing the 'high end' EM solutions are not coming to the party with the tensor calculus. (Who would go to that?!) The only point of Maxwell's equations existing, apart from existing applications (like radio, and QFT) is putting into numerical solvers. Engineers need not understand it quantitatively at all, because it is effectively useless.
--- Quote from: bsfeechannel on December 29, 2021, 08:52:09 pm ---It's a thought experiment. Thought experiments are designed to test the limits of a concept. You're not expected to really accomplish them. ...
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I disagree it's a thought experiment. Apart from the impracticality of scale, it's an eminently testable and calculable physical circuit, using any number of currently acceptable tools and individual interpretations. (Yes Veritasium's video somewhat trickily conflates concepts but I think that's his entire point - he's trying to very validly support that clickbait title with proof that electrical energy flows in fields. Which it has to, if the light bulb turns on before 1 second. Which we know it does. I disagree that it follows that energy does not flow in wires, but that doesn't alter the proof of concept Derek provides to blow minds.)
--- Quote from: bsfeechannel on December 29, 2021, 08:52:09 pm ---Avoiding Maxwell is not an option. Whether you are aware that what you doing is described by his theory or not. He's inescapable.
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Many things I might do are described by many theories people may hold and that I may or may not be aware of. That does not mean I'm using them! If I grow wings and become capable of flight (and do fly), that isn't because of some cosmic permission granted by the author of a theory of flight. It’s not a capability imparted to me by birds (unless my abilities come from observations of birds and what they do with their wings - in that sense Maxwell is responsible for radio, but he was also responsible for trichromatic colour photography, arguably as useful as radio). He doesn't stand alone (nor do his achievements, in the sense that I'm not aware of a gaggle of "Maxwellians" going round insisting that 'His' image is displayed on the corner of all RGB Bayer arrays - but where can I sign up?!).
adx:
--- Quote from: Sredni on January 01, 2022, 09:09:39 am ---...
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."
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This (italics mine). Is an example of an academic sermonising scientific hypothesis as fact. It may seem harmless, but results in generations(s) of disciples believing stuff.
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