General > General Technical Chat
"Veritasium" (YT) - "The Big Misconception About Electricity" ?
adx:
Re the apparent polarity issue in AlphaPhoenix's video, I dragged this orgy of self-centered insight up from the deep...
--- Quote from: adx on February 19, 2022, 03:47:41 pm ---
--- Quote from: adx on December 18, 2021, 02:19:09 pm ---If the scope were truly isolated (or ground lifted, depending on where EMC caps go) then the green trace should rise sharply more like the yellow.
--- End quote ---
and
--- Quote from: adx on February 15, 2022, 01:38:27 am ---I explained some of the problems with AlphaPhoenix's result many pages back, one of the main ones which distorts the send waveform I think is common mode coupling. I explained what I think it should look like, if it is measured with a better technique. Others did too, and went into quite some detail.
--- End quote ---
At 7:27 in the video is a diagram of the setup. The probe "reference GND" is the ground clip of the scope. This is tying one side of the pulse generator to Earth, loosely via extension cords and perhaps an inverter from the cars (described in discussions here at the time). The green probe, which is on the other side of the resistor, can thus not see the step directly from the step generator, because it is shorted to ground at the send end (by the ground clip). In essence it can only see voltage due to current getting around the circuit the long way, and a slow change of the GND voltage (which we can't directly see, because there is no probe measuring the voltage between this scope's GND and Earth under the desk).
This is not the way it's meant to be, but surprisingly the experiment still works. It's not necessarily an error if the person doing the test knows that taking this shortcut will still work. Again, I agree the green trace is "wrong", and this does represent the current in that resistor, and hence the current sent into that leg of the 'apparatus'. The other leg should be taking the balance, so it should be seeing nearly all the initial pulse missing from the green side (because that is shorted to ground).
From the clean white trace I can infer that the differential send current is probably fairly rectangular. But subtract the green trace and add the generator step, and that's going to make for a pretty messy voltage on the far side of the unprobed resistor, possibly best not to think about because it is guaranteed to confuse.
The situation would be the same but inverted traces (voltages) if the polarity of the generator is changed - other than that there is no difference and I likely would not test to confirm if I were doing the experiment.
--- End quote ---
Veritasium's new video is the same setup, minus the send resistors and current probing.
It's nothing to do with polarity, but which side the GND clip is attached to.
aetherist:
--- Quote from: adx on May 11, 2022, 01:06:08 pm ---Re the apparent polarity issue in AlphaPhoenix's video, I dragged this orgy of self-centered insight up from the deep...
--- Quote from: adx on February 19, 2022, 03:47:41 pm ---
--- Quote from: adx on December 18, 2021, 02:19:09 pm ---If the scope were truly isolated (or ground lifted, depending on where EMC caps go) then the green trace should rise sharply more like the yellow.
--- End quote ---
and
--- Quote from: adx on February 15, 2022, 01:38:27 am ---I explained some of the problems with AlphaPhoenix's result many pages back, one of the main ones which distorts the send waveform I think is common mode coupling. I explained what I think it should look like, if it is measured with a better technique. Others did too, and went into quite some detail.
--- End quote ---
At 7:27 in the video is a diagram of the setup. The probe "reference GND" is the ground clip of the scope. This is tying one side of the pulse generator to Earth, loosely via extension cords and perhaps an inverter from the cars (described in discussions here at the time). The green probe, which is on the other side of the resistor, can thus not see the step directly from the step generator, because it is shorted to ground at the send end (by the ground clip). In essence it can only see voltage due to current getting around the circuit the long way, and a slow change of the GND voltage (which we can't directly see, because there is no probe measuring the voltage between this scope's GND and Earth under the desk).
This is not the way it's meant to be, but surprisingly the experiment still works. It's not necessarily an error if the person doing the test knows that taking this shortcut will still work. Again, I agree the green trace is "wrong", and this does represent the current in that resistor, and hence the current sent into that leg of the 'apparatus'. The other leg should be taking the balance, so it should be seeing nearly all the initial pulse missing from the green side (because that is shorted to ground).
From the clean white trace I can infer that the differential send current is probably fairly rectangular. But subtract the green trace and add the generator step, and that's going to make for a pretty messy voltage on the far side of the unprobed resistor, possibly best not to think about because it is guaranteed to confuse.
The situation would be the same but inverted traces (voltages) if the polarity of the generator is changed - other than that there is no difference and I likely would not test to confirm if I were doing the experiment.
--- End quote ---
Veritasium's new video is the same setup, minus the send resistors and current probing.
It's nothing to do with polarity, but which side the GND clip is attached to.
--- End quote ---
Yes, i am ok with all of that. There might be always be some intrinsic asymmetry from the source, but for sure there is asymmetry from the position of the switch (symmetry needs 2 switches) plus as u say the ground/earth (ie the position of the source inputs).
Anyhow, it’s the nanoseconds that we are interested in in any such X, good nanovolts is just a possible bonus.
Ben Watson's 3D Maxwellian version of a lumped element transmission line model assumes a symmetric battery source & symmetric switching (ie using a switch at the positive terminal & at the negative terminal)(both magically working at the same time).
Sredni:
I resisted posting this since I didn't want to give wrong ideas to the 'original thinkers' in these threads, but since there already is some sort of discussion on how to mimic the behavior of the circuit with a mechanical model and the apparent necessity for an ether (in the mechanical representation) has already been thrown around, I figured... what the heck.
What follows in NOT a model, and is NOT an analogy for the circuit. It is JUST a pictorial way to illustrate the propagation of two different (albeit related) perturbations in the space occupied by the circuit. I call this a magi-mechanical model in that it employs MAGIC to perform its function. (It could probably be constructed by using some sort of active system or some clever use of preloaded springs or whoknowswhat, but... magic is a lot easier.)
Steady-state and the magi-mechanical model
Let's start with the steady state configuration: we have frictionless rail along which balls can move, a generator that raises these weights from a low level to a higher level, and a resistor that lowers them, converting the potential energy into heat. Heat extracts energy from the system. The whole circuit is attached to an elastic sheet in a manner that I will explain later.
steady state magi-mechanical circuit - https://i.postimg.cc/qR8D5JcY/screenshot.png
There are a few considerations to make
The generator
the generator can raise weight from the lower end to the higher end, but it only works if there is a ball in the lower end slot. With no ball there, it won't raise s*it.
Moreover, it has a rigid structure and when we 'flip the switch' it will rotate about a pivot point raising the elastic sheet in the process. The balls enter the generator with speed v0 and exit the generator with speed v0.
The rails or conduits
The rails, or conduits are like a chain, that can be raised or lowered by the nearby generator, but also by the membrane. They are kind of floppy and initially they can only be raised by the generator or the deformation in the elastic sheet, but once a ball gets on the chain link, it will make it snap into a horizontal position, carrying the sheet with them. How? By using magic.
(This is to mimic the propagation of surface charge that is associated with a current inside the wires)
The resistor
The resistor is another floppy (i.e. passive) element that can be raised by the sheet. It features a dissipation mechanism that takes the ball at its upper end and carries it down in a series of cups and dampers that turn the energy into heat.
The ball enters the resistor with speed v0 and also exit the resistor with speed v0.
dissipative mechanism - https://i.postimg.cc/K8Rqyrrt/screenshot-6.png
The resistor chain mechanism is weightless and kind of magically glued to the elastic sheet and therefore can be raised by the membrane (whose deformation does not have to take into account the weight of the resistor or the balls inside it).
Transient and perturbations in space
What happens during the initial transient? Well, the throwing of the switch is here represented by the tilting of the generator structure. The rigid structure bring the elastic sheet with it and the conduits immediately adjacent will raise locking into horizontal position - the other end will sink down bringing the rail/conduit down with it. A ball will flow into the lower slot of the generator and the motor will start raising the ball in the lower nearby horizontal rail slot. For every ball taken away from the lower side, a ball is put into the higher side of the generator.
As the balls move along the forming 'raised-lowered' rails, new parts of the conduits lock into horizontal place and the deformation of the sheet proceeds (at high but finite speed) ALONG the longitudinal structure of the circuit.
At the same time, though, the elastic sheet raised at the generator side changes the configuration of the sheet in all space around it, including in the transverse direction ACROSS the circuit. This perturbation of the sheet proceeds at a high but finite speed and when it reaches the resistor (much much earlier than the perturbation of the rails started by the generator arrives there) it will raise and lower its floppy body.
This deformation of the resistor (after a time d/c) will make the balls there fall into the dissipative mechanism, and a current will flow into the resistor well before the rail deformation has gone along the full path of the circuit. It will be a much lower current than that attainable at steady state, but a current nonetheless is flowing.
transient with two perturbations - https://i.postimg.cc/HsPz38Dn/screenshot-3.png
Also, the equivalent of KCL is dead here. We can have a current in the lower leg and a different current in the upper leg with no current at all in the rest of the circuit. And no, the balls are not one attached to one other, there is space for local accumulation and rarefaction. Only at steady state we can get a uniform distribution along the circuit and the analogous of KCL obeyed.
Not a friggin' transmission line
What is the purpose (in my deranged mind) for this magi-mechanical model? Illustrate the fact that we have two perturbations that proceed along different directions and that the transmission line model does not consider that 'complication'.
As a matter of fact a transmission line can be 'magi-modeled' by placing the generator on the short leg, and the resistor far away on the opposing short leg.
magi-mechanical model of a transmission line - https://i.postimg.cc/jjYzkz8x/screenshot-4.png
In this case both perturbations proceed hand in hand (this is to mimic the use of lumped component for the transverse phenomena) and a transmission line can model the long circuit.
But the magi-mechanical model for the wide circuit shows that in this case one kind of perturbation reaches the load well before the other. The alteration in the fied (here represented by the magical elastic sheet) is accompanied by a local spreading of the second type of perturbation near the resistor, but this is at a level that is well below that attainable at steady state.
magi-mechanical model of NOT a standard transmission line - https://i.postimg.cc/v8CLVFWx/screenshot-5.png
Is energy actually traveling?
A further consideration can be made about the transport of energy. Is energy traveling at all? In my eyes the energy put into the generator is used to change and keep a configuration of the elastic sheet (and borderline conduits) that makes it possible to extract energy in situ at the resistor.
What propagates for sure is the change in the field in all space around the generator. Then we can extract it wherever the new configuration of field allows us to.
(Now, the process of extracting energy can on its own alter the field, and this perturbation will propagate to the generator that might have to put more energy in in order to maintain the status quo).
TimFox:
In high-school physics class, ca. 1965, we had a mechanical demonstrator for one-dimensional transmission lines that used a dense set of transverse rods connected to a central torsion spring.
One could propagate a pulse down the rods and see reflections. Termination options included nothing (open circuit), fixed position (short circuit), and terminated (dashpot for viscous damping).
The propagation speed down the rods was appropriate for human eyesight to see the results.
If I remember correctly, there were different models (different characteristic impedance) to see what happens at discontinuities.
I think this old Mister Wizard demonstration uses the same unit.
hamster_nz:
--- Quote from: Sredni on May 11, 2022, 09:53:52 pm ---I resisted posting this since I didn't want to give wrong ideas to the 'original thinkers' in these threads, but since there already is some sort of discussion on how to mimic the behavior of the circuit with a mechanical model and the apparent necessity for an ether (in the mechanical representation) has already been thrown around, I figured... what the heck.
...
--- End quote ---
Wow! an epic amount of time and thinking went into that post!
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