General > General Technical Chat
"Veritasium" (YT) - "The Big Misconception About Electricity" ?
Naej:
With a Faraday cage, you removed (almost entirely) the capacitive coupling between the wire near the switch and the light bulb.
You also added a strong capacitive coupling between the wire and the cage (because the distance is tiny), and the cage is a transmission line.
So you'll get large reflections at entry/exit of the cage, which will die down after a millisecond, and the lamp will be in its normal DC state.
In the light point of view, your cage is made with double-faced mirrors with 2 tiny holes, and you suddenly switch a light on. After a millisecond, there will be as much light inside as outside.
(And of course, no need for Poynting's vector to explain anything)
SilverSolder:
--- Quote from: Naej on January 22, 2022, 08:04:17 pm ---With a Faraday cage, you removed (almost entirely) the capacitive coupling between the wire near the switch and the light bulb.
You also added a strong capacitive coupling between the wire and the cage (because the distance is tiny), and the cage is a transmission line.
So you'll get large reflections at entry/exit of the cage, which will die down after a millisecond, and the lamp will be in its normal DC state.
In the light point of view, your cage is made with double-faced mirrors with 2 tiny holes, and you suddenly switch a light on. After a millisecond, there will be as much light inside as outside.
(And of course, no need for Poynting's vector to explain anything)
--- End quote ---
Yeah, I had misunderstood the argument - thought there was something new in it :D
bsfeechannel:
--- Quote from: adx on January 22, 2022, 01:55:54 am ---Except for this:
https://en.wikipedia.org/wiki/Aharonov–Bohm_effect
:o
--- End quote ---
I find it amusing that we resort to quantum mechanics, which is much more complicated and less intuitive than classical electrodynamics, when we struggle with the latter exactly because it is unintuitive and complicated.
Anyway, the Aharonov-Bohm effect shows even more strikingly how the action is in the fields. Of course, Feynman has a chapter dedicated to the subject.
--- Quote ---What we mean here by a “real” field is this: a real field is a mathematical function we use for avoiding the idea of action at a distance. If we have a charged particle at the position P, it is affected by other charges located at some distance from P. One way to describe the interaction is to say that the other charges make some “condition”—whatever it may be—in the environment at P. If we know that condition, which we describe by giving the electric and magnetic fields, then we can determine completely the behavior of the particle—with no further reference to how those conditions came about.
--- End quote ---
The technical term for "avoiding the idea of action at a distance" is called locality. There's no telekinesis in physics, apparently.
Space is not an empty volume in front of you. It is an active player that provides the proper interaction between objects.
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.
adx:
I don't really follow your arguments from a logical sense, but I (think I) know what you mean so am happy to leave it there or even 'agree to a degree' (just made that up).
Best I can understand is that you seem to be saying / proposing / hypothesising / believing that a field is a real fundamental object in its own right, that exists independently of the particles that some say carry, produce or otherwise 'have' the field. They act through the field, or at least are composed of something like energy in the field (so in that sense the particles are subordinate to the field and do not carry field around). Kind of like an uberaether. My position is "I don't know".
But what I will say is that I never understood what the hoopla about "action at a distance" was and is. Say I'm 4 and pick up some magnets and play with them, I'll soon come to a conclusion that there is some invisible force acting between them. Then I'm 14 and playing with a vacuum chamber I made from a peanut butter jar and old fridge compressor (to make plasmas with EHT straight off the top of an EL509). I wonder if magnets act the same in there, so rig up a test (not something I've actually ever seen reason to do). Force does not change. My conclusion is "it goes through the vacuum". Later (much), the neighbour's cat comes visiting while I am flying a remote control helicopter, looks at my hands and the thing flying round and decides that it is not terrifying or edible because I seem to be controlling it somehow. It's as if I've got a string, or stick, but it's invisible, and that's no big thing because he is used to pretending the string or stick doesn't exist. Given the experimental capabilities of humans and philosophical prowess of cats, what more is there to know than "can't see it so don't know what it is"? Do we really want cats experimenting and humans philosophising over what it is?
Edit: Ok EHT not off that and probably not even an EL509, a shame the number of B&W TVs I destroyed.
adx:
--- 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.
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