Veritasium Electricity Video - Simulation Notes

Just some extra notes and clarification on simulating the Veritasium Big Misconception About Electricity video problem as a transmission line.

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#ElectronicsCreators #Veritasium #Simulation

[stevenspmd]

I love these debate videos. Practical engineering may rightly ignore such things but knowing the limits of your abstractions/models is also key to good engineering.

[framegrace]

According to Veritasium videao, this had no relationship to transmission lines or antennas, they hide that information very well . If veritasium title had been. "How long will it take the signal from one antenna to another at 1 m of distance", there would not had been any discussion and no clicks. The video was pure click bait.
Nowhere in the video is said that the cables must be at a constant distance on 1m for that to work, for example.

[vaapad]

If the lamp turns on at any current, it will turn on instantly from random electron movement in the wire.

[kreynolds]

For the first 1m/C seconds, I prefer a transmit and a receive dipole antenna model over a transmission line model because with a transmission line, a power source is connected to both lines at one end of a transmission line while a simple dipole antenna also has two wires connected directly to a power source but the wires go in different direction like they do in the example problem

[bartomiej]

"No matter for how long" i think that matters most, because i suspect most people understands this questions as turn on and stay lit, not just blinks, that could lead to big missconception.

[keithmasumoto]

YES! This the representation that people need to see. That power cords are comprised of two lines separated by a quarter inch.

[mb]

Derek has set up some kind of trick experiment and tries to tell people, electrical power is coming to their homes at least in parts through the air directly from the power plant. When flicking the switch he could have said that the transferred power after 1m/c will never be enough to light the bulb but we have to wait another full second and that with such a long wire we will experience some kind of on-off for a while until reaching steady state. He could have explained all that, but no, he leaves it in a mystical realm, basically saying that energy comes through the ether. And that's exactly what you can read in the comments, people are confused, miseducated and some even say that Tesla's Wardencliffe Tower is finally proven or other esoteric crap.

[RWoody]

I thought the spirit of the question was how energy gets from a source to a destination, not how some of the energy (ie only during the transition period after closing the switch) gets from the source to the destination.

[VisualElectric_]

The reason the bulb turns on is due to inductive coupling between the two conductors. The capacitive part of the energy transfer would be comparatively small. What we have in the initial moments is best described as a loosely coupled transformer.

To understand why, the distributed parameter model (with LC sections) requires an infinite number of infinitesimally small sections to model the line properly (this is possible with the telegrapher equations, see later). You can approximate the situation with fewer sections, but then you are forced to lump the capacitance in fewer, discrete places, whereas in truth, it is spread evenly along the line. In practice, this means the capacitance between the bulb and battery is vanishingly small. It's only when you lump this capacitance (and go to medium and short line models) do you notice the capacitive effect. In other words, a model with few sections is only capable of simulating electrically short lines. This situation calls for an electrically long line model where the initial surge is only "exposed" to one bit of capacitance at a time, not the whole lot (or substantial portions of it) at once. With this model, the capacitance is negligible in those initial moments.

Instead, the transfer of power is due to inductive coupling - just like a transformer. The transient current just after battery turn on will result in a changing magnetic field, and induce a voltage on the other conductor, lighting up the bulb. This is a well known phenomenon in the power industry. I have seen several studies looking at inductive coupling between power lines and, e.g. fences or other nearby metallic structures. Quite large voltages can result, especially when you get high frequency surges such as lightning strikes. You'll see such studies performed using frequency dependent line models such as the Jmarti or Universal line model in which the starting point is the solution to the telegrapher equations, where you use calculus to derive a model which *is* an infinite number of infinitesimally small sections (giving you V, I as function of position and time on the line).

[stephens]

I'm glad you pointed out the invalid use of the transmission line model. It's similar, but not just a pure, simple transmission line model, and using the transmission line model to represent the current transfer from one side to the other is not completely valid (it is only representative for end-to-end).
Even the capacitance across the leg is somewhat invalid for this purpose, because the capacitance per unit length is important (there's inductance for each infinitesimal capacitance). You can improve the accuracy by making your capacitances and inductances very very small, but for all except the first infinitesimal capacitor, the delay to the bulb becomes greater than 1m/c (yielding the more complicated power transmission that others have already modeled quite accurately).

[WRND]

That's all well and good, but how do I use this information to optimize my audiophile speaker cables? ;)
Cheers.

[derstrom]

The Falstad simulation was absolutely beautiful. Loved it!

[Jugge]

If 1/c is true then the wire length only needs to be 1 m in each direction and the ends may be open. Any "information" beyond 1 m is inaccessible to the circuit on that timescale according to the limiting light speed.

[rodc]

Maxwell was 50 years ahead of his time, if it werent for Maxwell's genius our electronics industry today: Domestic, Military, Aerospace, Space would be 1960/70s vintage, every so often when I turn on my computer and open the web browser I think that this technology simply wouldn't exist in our time if it weren't for James Clerk Maxwell. (Not to mention RGB first colour photograph etc...)

[amedeeabreo]

I just tried to write a comment on Vertasium's video and his channel is not allowing comments. He's gone into hiding now!

[bobwhite]

I finally went back to Veritasium’s vid and read the analysis he linked in his description. Interestingly enough, one of the analyses cleverly treated this as a superposition of a transmission line and an antenna. I encourage all to have a look - it was pretty slick (or should I say schmick?)

[SaschaUncia]

I'm a bit confused because this sounds like spooky action at a distance. For example imagine the following scenario...

- Say you have an LED bulb and a sufficient power source spaced one light second apart.
- Lets assume that we are using some kind of superconducting wire with nearly zero resistance to simplify things
- The wire stretches out in a straight line to relative right and relative left for 5 light seconds in either direction, meaning there is a 10 light second long segment connecting the power source and bulb, and a total of 20 light seconds length in wire.

So if you flip the switch the light will turn on in 1 second?

What makes it so that this particular light switches on, for example what if you have other bulbs and loops of wire. How do the electromagnetic waves 'know' to conduct energy to that one bulb within 1 second without tracing the full 20 light seconds worth of wire to find which one it is connected to?

What if you additionally have an astronaut 5 light seconds away, flipping a secondary switch on the line at the furthest point. Assume you both synchronized watches ahead of time, and are compensating for any relativistic effects from travel. You both close the circuit at the same time, does the light take 1 s to light?

What if the loop has been closed at their end for some time. You flip your switch and 1 s later the light turns on. At the same time the other astronaut opens their switch, will it take 1s for the light to turn off, or 5 seconds?

So many questions!

[johngreb]

You can`t "Ignore the Inductors" because they are simulating the speed of light on the line. You ONLY get an initial spike because you failed to add an initial inductor. There should be an steady current through the capacitance equivalent to 800 Ohms, enough to light the bulb faintly.

[fazergazer]

So in effect, the length of these loops could be infinite and they don’t really effect the fast transfer of field across the small gap. That local effect is what matters.
So no violation of speed of information transfer. We don’t rely on field transferring through the entire loop, just local capacitance. Just depends on this gap (1m, 2m or whatever)!

[nohous]

The intiution here is dependent on how are you actually used to interpret EM phenomena; whole LC transimission line concept is a hack to incorporate finite propagation speed of information to a simplified physical model which was invented to ease up things where length << wavelength.