General > General Technical Chat
"Veritasium" (YT) - "The Big Misconception About Electricity" ?
adx:
I had planned to extend this drawing for another post but this is topical now - on the existence of fields.
It refers to a concept I posted before, but the diagram might make it more obvious.
Take a vacuum (not mine!), it contains the entire universe, possibly a very small one, but enough space to know there is no charge.
Is there a field? Radio waves could theoretically travel if it's like ours, but there is no charge, so we'll never know. It would be a strange world (or universe) where there exists a facility for something which can never occur or even be guessed at - a philosophical uphill battle getting that to make sense. That would include space and time of course, but how confident could you be of a functioning EM infrastructure in such a place? If it is like ours, is there anything yet to be discovered in ours that could affect what is theoretically possible or impossible there?
1 electron: Is there a field? There is nothing else to interact with directly. Perhaps its radiation resistance could be measured, and the mass of distant space measured somehow to check where the energy went.
2 electrons: Is there a field? Static forces exist, and can be measured. It's like my magnets example above. You'd know there is a force, but any concept of a field would have to be pretty limited, or unnecessary, until you discovered radio. Then it might be pretty tough to test what is going on to form an opinion over how it works.
3, 4 electrons: Now you can start testing things more completely. Things like how it behaves in 3D.
Sredni:
--- Quote from: adx on January 24, 2022, 03:49:57 am ---
--- Quote from: bsfeechannel on January 23, 2022, 07:35:37 pm ---I like it at the end where Feynman shows where classical and quantum ED converge, i.e. give the same result, for when the "solenoid" is not microscopic, as it is in the Aharonov-Bohm experiment.
--- End quote ---
Ang on, didn't read that properly. The Aharonov-Bohm experiment is the size of a desk, if I have that picture right. I just very briefly looked at an explanation on Quora where it is compared to a (toridial) transformer - the windings are in a region of zero magnetic flux, yet they still pick up a voltage because of the enclosed flux. A "turn" is potential, I guess.
--- End quote ---
To my knowledge, the AB effect is a quantum effect that manifest itself on a microscopic scale (as bsfeechannel pointed out a few posts back). Very loosely speaking, it can be thought as being the consequence of the 'smearedness' of the wave function of the electrons: even if the little hard sphere we represent in our mind as being an electron is in a region without B, its wave function is spread out to encompass the microscopic solenoid and the region where B is.
It happens to be as magic as the interference of an electron with itself in the the double slit experiment. If we think the electron as a little hard sphere, then the double slit experiment with single electrons can only be explained by black magic. It appears that the little ball is capable of 'sensing' the presence of the slit it does not go through. But when you consider wave functions, that are delocalized, it seems a little less strange (while still remaining strange, but that is because we are limited to think in terms of either waves or particles).
The AB effect, an electron being able to sense the static magnetic field 'hidden' inside the solenoid, can thus be compared to the ability of an electron to sense the slit it did not pass through.
Trying to transpose this behavior to the macroscopic world is, in my view, trying to say that John, who entered the room through the front door, has also entered the room through the window. Or that, since in the quantum realm there is a tunnel effect, there is an appreciable probability that John has walked through walls. No, that probability is appreciable only if John is the size of an atomic particle and the walls are nanowide.
(A final note: in the case of the toroid in the macro world, we are able to 'detect' the B field hidden inside the infinite solenoid because it is changing and therefore the dA/dt brings into existence an actual electric field Eind in the point P outside the solenoid. Locality is saved. The AB effect is about a constant B field, so dA/dt is zero and there only is a time-constant A around the solenoid)
adx:
--- Quote from: rfeecs on January 22, 2022, 12:27:15 am ---... we know energy is propagating. We can measure it and we can calculate it. We know the wave fronts are moving and we know that since there is energy in the ...
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(emphasis mine)
That's a bit I had trouble with. We can't really, because it changes its direction.
adx:
--- Quote from: SiliconWizard on January 17, 2022, 08:56:39 pm ---
--- Quote from: adx on January 17, 2022, 02:47:45 am ---So yes, you can transfer energy from one wire to another at DC steady state and it happens all the time.
--- End quote ---
Can you show us? =)
--- Quote from: adx on January 17, 2022, 02:47:45 am ---The field effect does not reduce with distance, that is an illusion caused by objects appearing smaller as they go further away in space(time), so there is no limit to the spacing.
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That's quite fascinating. Can you show us?
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Finally, to answer these. For completeness, said I would.
Point 2: This is simply that the total flux (the "field effect") remains the same out to infinity. I had thought of adding that to my diagram above, but it doesn't work exactly for discrete charges like electrons. It is a bit tongue in cheek, but highlights that things seeming to get smaller as they get further away is an illusion, a property of space, not the things. And why scenes don't reduce brightness with distance. In the field view, the field is still there 'in full force' (it just spreads out). Indeed plane waves don't reduce in intensity, walls of charge don't either. But in the particle interaction view, there is this 1/r^2 effect and no need for the double entry accounting type of approach of defining an intermediate field.
Point 1: Energy transfers from one wire to another at DC steady state and it happens all the time:
--- Quote from: adx on January 05, 2022, 02:27:36 pm ---I suppose time-varying electric fields will be produced by flowing charge. If you consider that a circuit must have a return path, then an electron going forward will push on the electron coming back, taking work from it and putting it into the field, which is returned after it passes. I guess topped up by the relativistic effect which produces magnetism, but that will be unequal and store energy in the electric field while current flows. Maybe something like that is responsible for the Poynting vector behaving as it does here.
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bdunham7:
--- Quote from: Sredni on January 25, 2022, 11:38:48 am ---The AB effect, an electron being able to sense the static magnetic field 'hidden' inside the solenoid, can thus be compared to the ability of an electron to sense the slit it did not pass through.
Trying to transpose this behavior to the macroscopic world is, in my view, trying to say that John, who entered the room through the front door, has also entered the room through the window. Or that, since in the quantum realm there is a tunnel effect, there is an appreciable probability that John has walked through walls. No, that probability is appreciable only if John is the size of an atomic particle and the walls are nanowide.
--- End quote ---
:-+
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