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

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Naej:

--- Quote from: bsfeechannel on January 14, 2022, 09:00:03 pm ---
--- Quote from: Naej on January 14, 2022, 02:00:47 am ---tl;dr : energy flows in wires. Or in vacuum. Whatever.

--- End quote ---

Is the earth the center of the universe? YES, at least for 1500 years. If you don't live under a rock, you'll see that the sun, the moon, the stars and the planets all traverse the skies every day and every night around us. The planets have that little loop they do in their orbits, but that's all perfectly predicted by the theory of the epicycles.

If that is so, why don't we use it anymore these days? It is because Galileo pointed his telescope to Jupiter and it became pretty clear that calculating the orbits of its recently discovered moons would be a nightmare.

Galileo then came with the Galileo's invariance, a.k.a. Galileo's relativity, where all inertial frames are equivalent to each other and their results can be converted from one to another using Galileo's transformation.

This principle underpins Newtonian mechanics.


--- Quote ---One century later, Carpenter arrives, in 1989.
If you know a bit of multivariate calculus, definitely read his papers: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.205.4488&rep=rep1&type=pdf  http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.205.4597&rep=rep1&type=pdf

--- End quote ---

What the author is basically saying is that engineers are too dumb to understand energy in the fields (fields are counterintuitive, current as a fluid is not) so the author suggests that we embrace a concept abandoned by Maxwell and Heaviside because of its incompleteness.

As Maxwell himself pondered in his treatise below:


--- Quote ---547.] He [Faraday] observes, however, that 'the first thought that arises in the mind is that the electricity circulates with something like momentum or inertia in the wire.' Indeed, when we consider one particular wire only, the phenomena are exactly analogous to those of a pipe full of water flowing in a continued stream. If while the stream is flowing we suddenly close the end of the tube, the momentum of the water produces a sudden pressure, which is much greater than that due to the head of water, and may be sufficient to burst the pipe.

If the water has the means of escaping through a narrow jet when the principal aperture is closed, it will be projected with a velocity much greater than that due to the head of water, and if it can escape through a valve into a chamber, it will do so, even when the pressure in the chamber is greater than that due to the head of water.

It is on this principle that the hydraulic ram is constructed, by which a small quantity of water may be raised to a great height by means of a large quantity flowing down from a much lower level.

548.] These effects of the inertia of the fluid in the tube depend solely on the quantity of fluid running through the tube, on its length, and on its section in different parts of its length. They do not depend on anything outside the tube, nor on the form into which the tube may be bent, provided its length remains the same.

In the case of the wire conveying a current this is not the case, for if a long wire is doubled on itself the effect is very small, if the two parts are separated from each other it is greater, if it is coiled up into a helix it is still greater, and greatest of all if, when so coiled, a piece of soft iron is placed inside the coil. Again, if a second wire is coiled up with the first, but insulated from it, then, if the second wire does not form a closed circuit, the phenomena are as before, but if the second wire forms a closed circuit, an induction current is formed in the second wire, and the effects of self-induction in the first wire are retarded.

549.] These results shew clearly that, if the phenomena are due to momentum, the momentum is certainly not that of the electricity in the wire, because the same wire, conveying the same current, exhibits effects which differ according to its form; and even when its form remains the same, the presence of other bodies, such as a piece of iron or a closed metallic circuit, affects the result.

550.] It is difficult, however, for the mind which has once recognised the analogy between the phenomena of self-induction and those of the motion of material bodies, to abandon altogether the help of this analogy, or to admit that it is entirely superficial and misleading.
--- End quote ---

A Treatise on Electricity and Magnetism, 3d edition, J.C. Maxwell, pp 195-196.


--- Quote ---a) Derek insisted you use a counterintuitive (but correct) understanding of energy flow in a context where it is poyntless, claiming other ones are wrong, without proving they are wrong.
b) everything else is incorrect, except possibly the engineering history of the first transatlantic cables.

--- End quote ---

Well, we can go back to the epicycles. It is intuitive and we don't even have to learn the counterintuitive laws of Newton. But the scientific paradigm shifted long ago, so saying that the earth is the center of the universe may sound like a misconception these days. Kids don't even learn about epicycles in school.

--- End quote ---
What Maxwell is saying is that magnetic momentum does not behave entirely like mechanical momentum. He is right.

Perhaps you didn't get the memo, but many scientists are using a terrestrial reference frame, where the origin is at the center of the Earth. And they will continue to do so even if you laugh at them shouting "epicycles!", as they are not impressed.

Now I can see that you did not come up with an example which contradicts the JV law. Can you guess why? (They don't exist.)
So perhaps you should learn physics until you can find one, instead of shouting epicycles.

Sredni:

--- Quote from: EEVblog on January 14, 2022, 09:38:36 pm ---Enlarged text mine.
You've found comfort in a text from 1941? Ok, whatever makes you sleep well at night!

--- End quote ---

Dude, that's Stratton. One of the most cited textbooks in EM.
Do you think Poynting theorem has changed since then? No, it hasn't. In the context of classical electrodynamics Stratton, Schwartz, Panofsky & Phillips, and Jackson are "the" references. I've heard good things about Zangwill, "Modern Electrodynamics" -  I have not read it thoroughly, only a few pages here and there, though - but even if it is a 2012 text, do not expect it to say anything different from Panofsky Phillips or Stratton.

For example, Zangwill says that "The analogy between this equation and the continuity equation [...] reinforces the interpretation of the Poynting vector S as a current density of electromagnetic energy."
Regarding the circuit with a simple resistor it surprisingly goes even further: "It is clear from the diagram that energy flows out of the point dipole source, into the vacuum, and into the wire at every point along its length."

But he acknowledges the same points made by Stratton in 1941 and has a little paragraph that says "It may seem odd that the Poynting vector for a wire circuit does not predict energy flow parallel to the wire itself. This and other unanticipated features of some Poynting flows prompt some authors to define a Poynting vector using S = E x B/mu0 + curl X. The vector field X is chosen to make [the Poynting vector] point in more “natural” directions. The [above] definition does not disrupt Poynting’s theorem because the latter contains only ∇ · S. Relativistic considerations constrain, but do not completely eliminate, this arbitrariness in the definition of S.
There is no real problem in any event because the Poynting vector is not an observable."
Not different from what Stratton wrote in 1941.
And Zangwill is well aware of the progress made in physics since Pearl Harbour.

Point is: you have to choose a theory and stick to it.

Do you use voltages and currents, and consider current as a flow of charge carriers? Stick to classical ED (it automatically incorporates special relativity) and learn how to correctly apply Maxwell's equations (to the point of being able to tell that the Poynting vector does not point directly towards the battery - or even good conducting wires - at DC because you've seen a picture on Feynman where it points radially in, in a resistive wire).
Do you like to think of electrons in circuits as waves of probability? Stick to non-relativistic quantum mechanics. But forget about describing electrons moving inside the conductors and banging ions: it's a wave that's being scattered by the lattice potential. Then that parts in your videos where you say "engineers knows very well that..." becomes all false. Try to use QM consistently to describe EM phenomena and see how far you go in even the simplest circuit.
Are you ready to forgo semiclassical theories and wanna go full quantum? Then stick to QFT and start computing probabilities for everything. But then basically everything you said in your video becomes lies.

You can't have cake and eat it.

bsfeechannel:

--- Quote from: Naej on January 14, 2022, 10:54:51 pm ---What Maxwell is saying is that magnetic momentum does not behave entirely like mechanical momentum. He is right.

--- End quote ---

And, because of that, the analogy of current flowing in a wire like a fluid in a pipe is flawed.


--- Quote ---Perhaps you didn't get the memo, but many scientists are using a terrestrial reference frame, where the origin is at the center of the Earth. And they will continue to do so even if you laugh at them shouting "epicycles!", as they are not impressed.

--- End quote ---

Yes. Galileo showed that the center of the earth as a frame of reference is as good as any other frame of reference. I use it all the time.


--- Quote ---Now I can see that you did not come up with an example which contradicts the JV law. Can you guess why? (They don't exist.)
So perhaps you should learn physics until you can find one, instead of shouting epicycles.

--- End quote ---

Cool, let's learn physics together then.

EEVblog:

--- Quote from: Sredni on January 14, 2022, 11:02:52 pm ---Are you ready to forgo semiclassical theories and wanna go full quantum? Then stick to QFT and start computing probabilities for everything. But then basically everything you said in your video becomes lies.
You can't have cake and eat it.

--- End quote ---

Yes you can.
You can use the tools that work for you in your circumstances AND also have a theoretical debate over whether energy actually flows inside or outside the wire.
Just like you can happily and accurately use Newtonian Theory for most stuff.
Once again, the fundmental question being asked here is whether or not energy flows inside or outside the wire.
You've been going blue in the face saying it's always outside the wire because Poynting and classical theory says so. Now when challenged with QFT you seem to be taking the tact of "whatever way you want to look at it".
Are you now willing to admit that energy may actually flow inside the wire, depending on which way you want to look at it?

bsfeechannel:

--- Quote from: EEVblog on January 14, 2022, 09:48:38 pm ---
--- Quote from: Naej on January 14, 2022, 02:00:47 am ---tl;dr : energy flows in wires. Or in vacuum. Whatever.

--- End quote ---

I'm begining to think that Derek/Ponyting can no more correctly claim that the energy actually flows outside the wires than QFT says it flows mostly inside the wire.
--- End quote ---

You see? It is you that are saying that. What "QFT" professor said is just that the probability of an electron interacting with another in the wire is greater than that of an electron interacting with another one 1 m apart. You jumped automatically to the conclusion that the energy flows in the wires due to your bias.

That's how misconceptions spread.

The "QFT" professor said that her field of research is not related to QFT QED. I suggest you interview a specialist in the study of QED to analyze Derek's claims and provide an unbiased conclusion.

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