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"Veritasium" (YT) - "The Big Misconception About Electricity" ?
aetherist:
Some comments found on Veritasium's youtube.
The Science Asylum 4 hours ago
11:08 "And at that instant, the electric field inside the conductor is no longer zero..." Thank you! I felt like I was only person saying this out loud.
aetherist:
Some comments found on Veritasium's youtube.
AlphaPhoenix 5 days ago.
Fantastic revisit! The animations and the simulations were spot-on, and great at showing the difference between the transient “first-second” effect, and the steady-state “rest of time” behavior. The whole “expanding loop of current” thing is a great way to phrase it, because after that poynting loop expands to match the actual physical loop of wire, then stuff starts to behave normally and all of the power is transmitted around the loop very close to the wire. I still hold that for this simple circuit, turning on a lightbulb with wires much smaller around than they are long, the effect of surface charge vs internal charge is negligible, so you can ignore any skin-effect stuff and say that “mobile” electrons are indeed pushing on other “mobile” electrons using their fields, but I totally agree that that’s a simplification, just a simplification that makes the intuition a lot easier. I also need to do some math about how far the average “electron” is displaced in order to build the initial charge distribution around some typical circuit elements - axial flow is the only way I understand those charge distributions getting built, and this whole endeavor has made me think hard about what that means. Someday when I think I understand it better I’ll edit up my pt.2 response video - thanks for the shoutout! I’ve got a great experiment in the works to show the “expanding poynting loop”
adx:
I rewatched Derek's video after a week of sort of thinking about it (been busy).
I thought it was good - the aesthetics, and mash up of what's been going on in video land since the first one. The higher 'res' HFSS simulation was really spectacular and does help clarify details. A much better, cleaner, denser, correcter explanation and obviously very carefully chosen wording which clarified some things even after 'all this time'. The simplifications (like Drude model conduction) I think are ok for the general audience this is aimed at, and conceptually "not wrong".
But one part that did increasingly 'grate' (or nicer word for that) is where it said the marbles going through pipe model was a misconception (and some of the things about energy not flowing in the wires) - IMHO that's towing the line of physics convention, which may be well justified academically, but wrong to say something is a "misconception" if it is what is really happening:
I can't remember everything that was discussed in this thread without looking, but as far as I got, it was that the fluid in a pipe model is correct - pressure of electron fluid, constrained by a pipe (in this case solid metal). The pipe expands under pressure, a mechanical pressure. The forces are the same thing - mobile, fluid. They all push on each other in the fluid similar to a normal fluid (barely compressible, electrically neutral, mobile). (The difference about the pipe is in the constraint - pipe wall, surface charge between empty space and neutral fluid.) So they do very much push each other down the wire, and it is how energy is transmitted.
But it isn't necessarily where the energy travels - I'll choose to steer away from the "path of energy" argument (like Sredni's question) after coming up partly blank a coupe of months ago. No one knows where (or even if). Thinking about the fluid 'analogy' of a hydraulic system in a digger (again) - how can the energy travel in the pipes, if it is the pressure difference between them that does the work? If it is in the space between the fluids (and definitely not in the fluid), where does the energy travel? (Rhetorical - I chose to steer away. Also combining quantum surface effects with speed-of-light energy transfer, things start sounding awfully like Aetherist's electons.)
So the marbles model is at worst "misleading".
Anyway, I like to draw over scope screenshots too, below is my first hack at working out a 1m transit time (without checking, admittedly if it had come up with something like 5ns then I might not have posted the PNG):
aetherist:
--- Quote from: adx on May 09, 2022, 01:52:56 pm ---............But it isn't necessarily where the energy travels - I'll choose to steer away from the "path of energy" argument (like Sredni's question) after coming up partly blank a coupe of months ago. No one knows where (or even if). Thinking about the fluid 'analogy' of a hydraulic system in a digger (again) - how can the energy travel in the pipes, if it is the pressure difference between them that does the work? If it is in the space between the fluids (and definitely not in the fluid), where does the energy travel? (Rhetorical - I chose to steer away. Also combining quantum surface effects with speed-of-light energy transfer, things start sounding awfully like Aetherist's electons.)
So the marbles model is at worst "misleading".
Anyway, I like to draw over scope screenshots too, below is my first hack at working out a 1m transit time (without checking, admittedly if it had come up with something like 5ns then I might not have posted the PNG):
--- End quote ---
On my copy i wrote a delay of 4.1 ns. But this was not an accurate estimate, your 3.0 ns is probly more accurate.
Actually i had another go at it myself & it came to 2.2 ns.
Veritasium intentionally avoided using a 50 ps/div scale, he went for a 50 ns/div scale, koz he didn’t have any answers for the initial rise & the initial plateau.
What is your own explanation for the rise & plateau?
aetherist:
--- Quote from: ejeffrey on May 04, 2022, 05:33:19 am ---
--- 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.
--- End quote ---
Berni & TimFox know that Velocity Factor duz not tell us the speed of elekticity. Velocity Factor is simply a radio ham fudge factor that gives good numbers for antennas.
Berni & TimFox know that Velocity Factor changes with GHz. Hence it has little to do with the pure speed of elekticity.
Berni & TimFox know that there is no experiment or test that has ever been carried out that links Velocity Factor to the speed of elekticity. Not for bare wire, not for insulated wire.
Any/every proper test will show that insulated wire has a speed of elekticity of 2c/3.
Berni & TimFox don’t know that it is not simply what is inside a coax that determines the speed of elekticity.
The speed of elekticity along a coax is the sum of the speed of elekticity on the Cu wire, & the speed of elekticity on the outside of the sheath (which is usually fully insulated).
Seeesh, i am getting tired of casting pearls.
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