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

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hamster_nz:

--- Quote from: bsfeechannel on May 03, 2022, 05:49:12 am ---
--- Quote from: Naej on May 02, 2022, 10:02:47 pm ---There's nothing more absurd than looking at physics equations and say "how?", it's not a religion, it's an axiom. ::)

--- End quote ---

Forget the equations. What I'm talking about is how exactly an electron exerts force on the others 1 m away. Does it have a barge pole to poke their fellow subatomic particles at a distance?

--- End quote ---

Ignoring magnetism, in classical theory charges respond to the local gradient of the electric field. And the value (and therefore the gradient) of the electric field is influenced by the locations of the charges.

Much like the same way apples fall to the earth due to gravity, and the locations of mass define the gravitational field. There is no string pulling the apple down. It just does what comes naturally.

Naej:

--- Quote from: bsfeechannel on May 03, 2022, 05:49:12 am ---
--- Quote from: Naej on May 02, 2022, 10:02:47 pm ---There's nothing more absurd than looking at physics equations and say "how?", it's not a religion, it's an axiom. ::)

--- End quote ---
Forget the equations. What I'm talking about is how exactly an electron exerts force on the others 1 m away. Does it have a barge pole to poke their fellow subatomic particles at a distance?

--- End quote ---
It changes the potential, and electrons are sensitive to potential, and in particular its gradient.
How does an electron grow an electric field by the way? It waters it, until a proton comes near it and reaps most of what was sown?

--- Quote from: bsfeechannel on May 03, 2022, 05:49:12 am ---But since you are obsessed with antennas, when exactly a piece of conductor decides it is not a wire anymore and becomes an antenna?

--- End quote ---
They always are. Often they are poor antennae at most frequencies, which limits interference.
How do you decide when exactly a wire becomes a coil? A capacitor?

ejeffrey:

--- Quote from: Berni on May 02, 2022, 04:36:57 pm ---
--- Quote from: TimFox on May 02, 2022, 02:09:31 pm ---A quantitative discussion of the effect of normal insulation layers on velocity factor in antenna construction:
https://lowpowerlab.com/guide/rf-best-practices/velocity-factor/
Summary:
0.95 for bare copper wires
additional factor of 0.95 to 0.98 when adding normal insulating materials (PVC, polyethylene, PTFE)
These factors are important when calculating antenna length.

To get down to 0.66, you need a coaxial construction such as RG-58/U with solid polyethylene dielectric
With RG-62A/U, which has an internal construction which is roughly half air and half polyethylene (annular geometry), the characteristic impedance rises to 93 ohms, and the velocity factor is 0.83.
Foamy dielectrics have similar velocity factors.

--- End quote ---

Yep this is more what i would expect, in the order of single digit percent difference from adding insulation.

For the kind of precision Veritasiums experiment is working with this certainly would not make much of a difference. The experiment works fine and shows expected results. It just doesn't clearly show the 1m/c delay claimed in the original video.

--- End quote ---

It doesn't show the exact number it particularly clearly but it does show it.  The yellow trace *starts* rising close enough to 3 ns after the green trace turns on.  It does takes about 15-20 ns to reach the ~5V plateau.  This is to be expected, and should show up in the HFSS models, but doesn't really detract qualitatively from the point: "the load begins to turn on significantly in a time approximately light crossing the gap".  Yes, at exactly 3 ns the current is still quite small but it it rises rapidly to a significant voltage.  Arguing about the precise dynamics is basically already conceding the point of the whole thought experiment.

Given the nice setup with rigid metal pipe on supports I would have wanted to slide the rods closer together, say 0.5 m and see how that moved the trace.  But I don't know that that would have actually been helpful for the target audience.

aetherist:
Some comments found on Veritasium's youtube.
electroBoom        5 days ago (edited)
This was a greatly detailed video and I think we are pretty much on the same page! Thanks for the shoutout and going through the trouble of clarification.
P.S. by the way, the resistor in your experiment didn't quite match the lien impedance, other you would get half your supply voltage right away. But I mean with such small capacitance and inductances, the probing itself could have added some parasitic components to the lines.
PPS: Like I said above "pretty much on the same page"! It is a complex subject, and I think some nuances could have been addressed better. Maybe Derek and I could sit together and react to nuances to clarify things!
Veritasium             5 days ago
We were all initially expecting half the applied voltage. BUT we modelled the circuit including coupling the wires on the left side of the resistor to the wires on the right side. In that case you get less than half and then the overshoot.

Alex       10 hours ago
just admit you were wrong
electroBoom         5 hours ago
 @Alex  ?! Why? I wasn't, and Derek doesn't say I was wrong
Alex           3 hours ago
 @ElectroBOOM  well from what I rembered from your video you said Derek was wrong and he explained why he wasn't
So that means you were wrong when you claimed he was wrong.  And I know there is room for interpretation in both of your vid.

aetherist:
Some comments found on Veritasium's youtube.
EEVblog   4 days ago (edited)
Happy that you finally did the follow-up video. It's excellent and well thought out and adds some excellent new detail. It won't stop the nerds arguing though, the EEVblog forum thread on the video is up to 75 PAGES of debate, LOL. The argument comes down to the fact that most practical engineers do not need to think in these terms, especially at DC. But I think you can sleep well at night after this one.
The only thing I didn't see mentioned was the Quantum Electrodynamics (QED) hypothesis that might ultimately trump Poynting and Maxwell when it comes to energy flow inside vs outside the wire. But I can understand how that might side track this video completely.
I know the Poynting/Maxwell math still works out for DC, but it's just The Vibe. So it's inside the wire at DC for this crusty electronics engineer :-P
Well done.
Comment on EEVblog by mad aetherist    1 second ago
 @EEVblog  I dont think that QED calcs could give numbers for delays (& voltages) that accord with what was found for the induced trace for the bulb/resistor in any such experiment (eg Veritasium's)(eg AlphaPhoeinix's etc). Or even close.
And, if the numbers do accord, what does it prove or confirm or support, almost nothing. Praps it would support that there is an aether.


EEVblog      4 days ago (edited)
 @tpog I was thinking of finding the world expert on QED and having a chat, anyone know who that is? I think that if you can do a physical experiment to prove QED and energy flow inside a wire, you'd win a Nobel prize. and change physics forever. And that's the problem with discussing it, AFAIK there is no practical experiment confirming it. I tried to read some researc papers on it, but my head exploded.


EEVblog    4 days ago (edited)
 @EpicBunty  Do we know everything? - Probably not. QED sound promising, and if true it likely trumps Maxwell/Poynting theory. In the same way that Einsteins general theory of relatively up-ended Newtons.
What we already know - Maxwell/Poynting is correct, because it provides a method to explain things that verifies with actual measurements. But we also still use Newtons laws to do lots of practical stuff, there is just a higher level theory available. We can't be 100% sure that a higher level theory above Maxwell/Poynting does not exist. And even if there is, for almost everything we'd still use Maxwell/Poynting anyway. And as Derek explained, we still use Ohms law and lumped transmission line theory, and transformer theory, and antenna theory to do practical stuff, because we don't need to fuss over the details or exactly how the energy flows.
Dragrath1      4 days ago      @EEVblog  Yeah the problem with trying to do a practical modelling of this is that  the Feynman path integrals for it mean that there are actually infinite integrals which have to be computed covering every single possible quantum interaction. These terms rapidly decay way to have negligible effects on the final calculation the larger their action is but as you start scaling the system to macroscopic sizes of a circuit even the number of relevant calculations you would need to produce a result using QED blows up towards infinity as the number of possible interactions increases.  With a powerful quantum computer it actually probably wouldn't be that hard to do as it could compute every path simultaneously but in the absence of that computational irreducibility rears its ugly head and the measurement precision limits you ability to robustly test the results.

the Feynman path integral is from a theoretical perspective beautiful and elegant but from a practical prospective it is so exceptionally unwieldly that you will never quite get the result you want within finite time.

EEVblog           4 days ago
 @Dragrath1 Yeah, I would not bet on being able to come up with practical measurement that can prove QED, but I would not rule it out either. Nobel prize on offer for the one that does though.

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