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

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Naej:
Maybe there's a simple word for a build-up of surface charges on two opposing conductors separated by a dielectric?

SiliconWizard:
Fields galore =)

aetherist:

--- Quote from: Howardlong on December 08, 2021, 09:34:38 pm ---I re-did the ladder line tests I ran a few days ago to demonstrate the ~80ps delay over the 24mm wire spacing.
I used the same probe to probe the "switch" (the scope's integrated TDR, cyan reference trace) and the bulb side (green trace) so as not to introduce skew.
The cyan trace was taken at 10mV/div and the green at 2mV/div, so there's significant attenuation before we approach DC steady state.
The yellow trace is the TDR trace which you can't get rid of without turning off the TDR: the TDR triggers the scope and turns on a long time before the displayed traces, it has to propagate through the cables to the DUT, note the trace delay of ~27ns.
I measured the time between the beginning of the two rising edges, at about the 10% level.
(The scope's pretty dusty: I had a ceiling collapse some months ago in the room adjacent to this, and it's still being repaired, so things get pretty dusty round these parts.)
--- End quote ---
Nice. I have not seen any comments re your experiment.
I did not know that old scopes had 20 GHz -- how much did they cost new? -- how much nowadays secondhand?

It confirms that some kind of crosstalk (mainly radio i suppose) crosses (the 24 mm) at c m/s.
I would like to analyse your results, could u please advise....
1. The rise time of the pulse?
2. The fall time of the pulse?
3. The overall time of the pulse -- or the flat time (ie total time minus the rise & fall)?
4. Or was it a step pulse, ie with no fall?
Thanx.

aetherist:
Howardlong messaged me the following info.
Rise time 10-90% at the scope is 36 ps. By the time it gets to the feedpoint, it'll be about 45 ps due to dispersion in the coaxial feed.
Fall time looks similar visually but I didn't take a measurement. Pulse width is 608 ps.

Howardlong has already mentioned that his signal crosses (first reaches) to the opposite wire in  80 ps which he says accords with the speed of light for the  24 mm distance tween the pair of wires in his  450 Ohm antenna ladder line. Howardlong in effect says that this supports Veritasium's expectation that Veritasium's bulb can possibly light (start to light) in 1/c seconds (ie 3.3 ns for Veritasium's 1000 mm spacing).

These kinds of transients have at least say 4 stages.
I wanted to have a closer look at Howardlong's experiments to look at the first stage, stage-1 of his transient. But i will come back to that another day.
Today i will jump ahead & look at stage-2 of his transient.

Howardlong X using 4 ft of ladder antenna line (wires 24 mm apart). He got 12 mV, with 58 mV in the other wire, which is 20.7% (20 GHz scope).
Schantz X using 100 ft of 300 ohm twin lead antenna line (wires 7 mm apart). He got 60 mV, with 340 mV in the other wire, which is 17.6% (100 MHz scope).
AlphaPhoenix X using 1000ft of 24AWG  enameled copper wire (wires 250 mm apart). He got 0.2 V, which climbed to 1.7 V, which is 11.8%(100 MHz scope). Actually his source is 5.0 V, so 0.2 V is 4.0%.
Silicon Soup (youtube) does a Finite-Difference Time-Domain simulation (1000 mm), gets a 0.3 mA signal from a 1.47 mA current, which is 2.0% 20.4%, for a mini-version of the Veritasium circuit. I don’t know how his pseudo-signal happens (its something to do with Maxwell)(displacement current perhaps).

All of the above percentages are astonishingly high. But i think i know what happens.

A step signal (voltage)(current)(Heaviside might say energy current)(Dollard might say impulse current)(whatever) propagates say to the right along the right half of our circuit, along the say bottom wire.
The bottom wire in that half is gradually flooded with negative charge, starting at the source (at the midpoint of the circuit), the flooding progressing to the right towards the short at the end.
The growing negative charge on the surface of the bottom wire gradually repels more & more free surface electrons (conduction electrons) on (along) the top wire, some go right (to the end), & some go left (to our bulb).
The electrons pushed right (along the top wire) tend to bunch up, because they are flowing in the same direction as the propagating step (in the bottom wire).
Actually, the free surface electrons in the top wire flow much more slowly (say c/100,000)(in the plastic insulation) than the step (2c/3)(in plastic), hence they are overtaken & left behind.
But, their wavefront propagates much faster (along the top wire) than c/100,000, perhaps c/100, perhaps c/10  (still thinking). Anyhow, the wavefront (along the top wire) too is overtaken.
The result is that say 50% of the escaping electrons in the top wire go left & 50% go right.
The electrons flowing left create a flow of electrons flowing left through our bulb, which manifests as a voltage drop across our bulb.
Our bulb turns on (weakly) a little after d/c seconds, ie as soon as (enough) electrons start to flow (leftwards) through the bulb on our top wire.
Our bulb glows brighter as the flow of electrons through the bulb increases.
After a short time the flow through our bulb reaches its initial maximum (say 10% of the current in the bottom wire).
[In the Veritasium gedanken (wire spacing d is 1000 mm) this would be a little after 1/c.]
Eventually the step (propagating right) in our circuit will get to the end of the bottom wire & will enter the top wire (via the short), & go to our bulb (while overtaking most of the electrons escaping to the left).
While the step is in the top wire it will push a much greater number of free surface electrons in the top wire towards our bulb, however this extra (temporary) current will lag the step (it might show as a hump on the scope).
When the main signal reaches our bulb the bulb will achieve full brightness, ie there will be a big sudden jump step in the voltage (followed by the aforementioned hump).
[In the Veritasium gedanken the main signal would reach his bulb in 1 second (his half circuit is 1 light second long).]

Regarding conduction electrons deep inside our top wire, these might drift left & right, in which case they would add to the current (at our bulb), but i reckon that any such drift would be insignificant.
However, conventional theory has it that this internal drift gives us 100% of what we call electricity.
I reckon that the induced drift in our top wire would add less than 1% to the initial current through our bulb.
Later, well after the main current first arrived, drift would account for nearnuff zero% of the current through our bulb.
And likewise surface electron flow would probably account for nearnuff zero%.

The electrons escaping to the left will give a current & voltage (signal) at the midpoint of our top wire (ie at our bulb). The size of the signal will depend on the wire spacing. The signal will begin to grow as soon as the E×H radiation reaches across, ie the delay is d (metres)/c (m/s), where d is the spacing, & c is the speed of light in the medium (usually air). More exactly, the delay will depend on the location of our switch, relative to our bulb.
[In the Veritasium gedanken this switch-to-bulb distance is approx the same as the spacing tween his wires anyhow.]

I doubt that a (simple conventional) LCRX lumped element transmission line model can predict transient current, using a simple LCRX paradigm, using simple speed of light.
Any such model needs smarter components.
And truer speeds (& truer flow of surface electrons).
However i have never had any hands-on experience with transmission lines, or TL models (or the application of electricity theory of any kind).
However the repulsion of the electrons from (along) our top wire is not unlike the action of lots of little capacitors tween the bottom wire & the top wire.

Perhaps someone could do a (simple conventional) transmission line model for Howardlong's experiment.

adx:
A lot of "advanced" thinking there, most of which I think I follow, but to me at least some is as confusing as the academic textbook treatments (with their diagrams of imaginary field lines, surface charges, and equations presented as some kind of reality in their own right).

I know it's only a work in progress and won't suggest it needs to fit this bill, but what I yearn for is some kind of description of rational physical reality which ultimately ties in well to experimental and numerical experience.


--- Quote from: aetherist on February 01, 2022, 09:48:22 pm ---... gets a 0.3 mA signal from a 1.47 mA current, which is 2.0%, ...

--- End quote ---
(original formatting)
20%?


--- Quote ---All of the above percentages are astonishingly high. But i think i know what happens.

--- End quote ---

To me and some others here, these results were astonishingly low. For a properly terminated transmission line (which the arms of this circuit can be) and differential drive (which is impossible for the arms because they are driven with a common mode voltage), the initial voltage and current should be 50% of the steady state.

I don't know what "free surface electrons" are, nor why they should flow at such extremely high speeds "in" the insulation (I assume you mean the interface between wire and plastic). c/1000000 is 300m/s, compared with a drift velocity of somewhere around say 0.00001m/s expected at ~~10mA in the wire. (That's about 10000000 times slower.) It doesn't sound like you mean a skin effect, where electrons go fastest in the outer portion of a wire.

One thing about a wavefront overtaking the 50% of electrons who go right, is that this wavefront travels at the speed of light, so not only does it overtake those electrons in this particular case, but there is nothing which can overtake it in any situation. In the simulations you can see the calculated spherical wavefront match the speed of the signal along the wires. The pushing force of the electrons is delayed by 1/c too, so by the time the force reaches the electrons in the top wire, the wavefront has already gone past that x position along the region of the bottom wire. The wavefront is one and the same thing as the pushing force. It's hard to think of it in those terms (that a force can propagate in such a visually defined way through 'nothing'), but if we accept that the speed of light is a thing, then no other result is possible - we are watching the fabric of time itself in action.

From this thread I have learned there is no more to electricity than this pushing force, and resultant movement of mobile charge carriers (in this case electron drift within the confines of wire). Pulling forces exist with positive charge carriers and also an absence of negative charges.

I don’t believe any of the humps and bumps in Howardlong's result are due to any sort of difference between electron movement and what is conventionally known (EM, capacitance, magnetism). To me it's mostly down to measurement (and generator) risetimes and non-idealities. For those features visible in the simulations, it's possible to probe the simulation for understanding.

I was wondering if this experiment (eg AlphaPhoenix's) had proved some effect which has remained undiscovered (or more likely unnoticed), but there is very little to suggest that there is anything other than something obvious and known going on.

Or rather it would be, if people generally understood how electricity works.

Someone working in the field (pun always intended) will gain a very good intuitive understanding of how electricity behaves, but can remain completely in the dark as to what it is. I think this is down to education of the subject being so physically abstract, to the point that the teachers themselves undoubtedly do not understand it. Concepts have not changed in 150-100 years, relying almost entirely on mathematical descriptions from some of the early greats in the field. I think their insights are sometimes forgotten next to their maths. Textbooks have formed a strong collection of opinions, trotting out the same received truths, but their focus is on how to best educate students, not to clarify the world's "description of rational physical reality" mentioned above. Somewhere along the way, the meaning has become lost.

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