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

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bsfeechannel:

--- 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.

EEVblog:

--- Quote from: Sredni on January 12, 2022, 09:09:47 pm ---Note 1: Regarding the transformations so slow as to be considered almost static so they would not lose energy to radiation, I have found comfort in

    Stratton,
    Electromagnetic Theory
    1941:

p. 131, italics mine

--- Quote ---"Poynting’s Theorem: In the preceding sections of this chapter it has been shown how the work done in bringing about small variations in the intensity or distribution of charge and current sources may be expressed in terms of integrals of the field vectors extended over all space.
The form of these integrals suggests, but does not prove, the hypothesis that electric and magnetic energies are distributed throughout the field with volume densities respectively

   fig densities formulae

"The derivation of these results was based on the assumption of reversible changes; the building up of the field was assumed to take place so slowly that it might be represented by a succession of stationary states".
"It is essential that we determine now whether or not such expressions for the energy density remain valid when the fields are varying at an arbitrary rate. It is apparent, furthermore, that if our hypothesis of an energy distribution throughout the field is at all tenable, a change of field intensity and energy density must be associated with a flow of energy from or toward the source."
--- End quote ---

On the arbitrariness of the assumptions relating Poynting's theorem Stratton has this to say:

p. 133

--- Quote ---"As a general integral of the field equations, the validity of Poynting's theorem is unimpeachable. Its physical interpretation, however, is open to some criticism. The remark has already been made that from a volume integral representing the total energy of a field no rigorous conclusion can be drawn with regard to its distribution. The energy of the electrostatic field was first expressed as the sum of two volume integrals.
Of these one was transformed by the divergence theorem into a surface integral which was made to vanish by allowing the surface to recede to the farther limits of the field. Inversely, the divergence of any vector function vanishing properly at infinity may be added to the conventional expression u = 1/2 E.D for the density of electrostatic energy without affecting its total value. A similar indefiniteness appears in the magnetostatic case."
--- End quote ---

But all in all

pp. 134-135, bold mine

--- Quote ---"The classical interpretation of Poynting’s theorem appears to rest to a considerable degree on hypothesis. Various alternative forms of the theorem have been offered from time to time,’ but none of these has the advantage of greater plausibility or greater simplicity to recommend it, and it is significant that thus far no other interpretation has contributed anything of value to the theory.
The hypothesis of an energy density in the electromagnetic field and a flow of intensity S = E x H has, on the other hand, proved extraordinarily fruitful. A theory is not an absolute truth but a self-consistent analytical formulation of the relations governing a group of natural phenomena. By this standard there is every reason to retain the Poynting-Heaviside viewpoint until a clash with new experimental evidence shall call for its revision."
--- End quote ---

Now, what experimental evidence have we?

--- End quote ---

Enlarged text mine.
You've found comfort in a text from 1941? Ok, whatever makes you sleep well at night!

EEVblog:

--- 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.
Except that QFT makes more intuitive sense if you take it to the most simplistic case (but very realistically practical) of DC in a huge diameter conductor.

SilverSolder:

For practical purposes such as sizing of wires, it is probably safer to stick with a working assumption that the energy flows inside the wires!  :D

SiliconWizard:
A lot of the "debate" coming more from using different (or even vague) definitions and a philosophical approach of science rather than experimental, it can probably go on forever. =)
Just like with the KVL one.

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