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I bought 1000 meters of wire to settle a physics debate [video]

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Re: I bought 1000 meters of wire to settle a physics debate [video]

#81

Post by vmilner »

tgsovlerkhgsel wrote: post #70
amelius wrote: post #45

This is basic transmission line theory. https://en.wikipedia.org/wiki/Transmission_line

It may be basic, but just the _existence_ of this field wasn't something that was on my radar, let alone all the details and implications. This was certainly the most interesting and enlightening set of videos I've seen this year. I particularly like this one because "I want to get an oscilloscope and see what is actually going on" was my first thought, and this video saves me the effort of trying to set up what woul…

The history of transatlantic cable-laying is extraordinary (and didn't work for several attempts because the theory of the field around the cable wasn't properly understood).

Re: I bought 1000 meters of wire to settle a physics debate [video]

#82

Post by bee_rider »

kreetx wrote: post #30
umvi wrote: post #16

Earlier quoted context omitted.

200uA of current flows through the lightbulb instantly, but it doesn't reach full current until speed of light delay.

A follow-up question: would there be no tiny change in the graph if the wires exiting the battery were further away from the wires immediately entering the light bulb?

Yeah -- nothing mysterious is happening, the electrons coming out of the battery are just causing an electric field, which causes current in the wire near the 'lightbulb.' This electric field obeys the c speed limit, so if the battery terminals were far away from the 'lightbulb,' there'd be a fundamental physics limitation, the current couldn't start until at least d/c (where d is the distance).

More likely the electric field would be too weak to measure, but that's not fundamental -- you would just have trouble finding a sensitive enough 'lightbulb.'

Re: I bought 1000 meters of wire to settle a physics debate [video]

#83

Post by userbinator »

amelius wrote: post #45

This is basic transmission line theory. https://en.wikipedia.org/wiki/Transmission_line

I've been partially following the discussions around the original Veritasium video and all that it's caused, and my thought was basically the same: the masses are just rediscovering what was known over a century and a half ago and that theory has found countless applications in communications and power distribution for roughly as long. IMHO that's not a bad thing, but to present it as something novel is.

Re: I bought 1000 meters of wire to settle a physics debate [video]

#84

Post by a9h74j »

jarenmf wrote: post #57
JshWright wrote: post #43

Earlier quoted context omitted.

> I think one of the issues with it is that it's a bit pedantic, but also ignores other issues, that invites other people to be pedantic about it. I think the video is intentionally misleading. He got a taste of how "successful" a controversial video can be with the "Wind powered car going faster than the wind" thing, and he's leaning into that. I just don't see any other explanation for how he chose to frame the pro…

That's unfortunate because his content used to be very good and this video seems only seeking engagement at a very shallow level, e.g. doesn't even mention transmission lines.

My early thought was that, at the very least, Poynting Vectors deserve a video but Transmission Lines also deserve a video.

Here's a problem I recall from Jackson which might (or might not) provide a missing link:

Given two parallel conductors of arbitrary shape, prove that the product of capacitance-per-unit-length and inductance-per-unit-length is a constant (i.e., independent of profile and separation).

I remember finding a suitable answer, but I can't for the life of me remember how.

Re: I bought 1000 meters of wire to settle a physics debate [video]

#85

Post by Jansen312 »

jarenmf wrote: post #57
JshWright wrote: post #43

Earlier quoted context omitted.

> I think one of the issues with it is that it's a bit pedantic, but also ignores other issues, that invites other people to be pedantic about it. I think the video is intentionally misleading. He got a taste of how "successful" a controversial video can be with the "Wind powered car going faster than the wind" thing, and he's leaning into that. I just don't see any other explanation for how he chose to frame the pro…

That's unfortunate because his content used to be very good and this video seems only seeking engagement at a very shallow level, e.g. doesn't even mention transmission lines.

Watch his vid again. Transmission line mentioned. He even use the issue with putting cable across the ocean having issue as a possible example explain his thought experiment. Could it be you used to watch his vids in full and remember and not so much for this one?

Re: I bought 1000 meters of wire to settle a physics debate [video]

#86

Post by soheil »

everybodyknows wrote: post #6

Anyone care to give us a Too Long; Didn't View?

Technically there is a very small current that flows through the circuit almost right away due to capacitance and inductance properties of the circuit, so Derek was right technically. That current won't be enough to turn on the light bulb. The rest of the current that actually turns on the light bulb takes some time to reach the bulb because the wire is so long and electrons travel with the speed of light along the wire [0].

[0] actually electrons don't move that much, instead electrons pushing against each other on the wire cause a ripple, it is this wave that moves along the wire and turns on the bulb.

Re: I bought 1000 meters of wire to settle a physics debate [video]

#87

Post by Flankk »

He connected an oscilloscope to the circuit in parallel. The oscilloscope has an unknown level of isolation between probing circuits. It cannot be said that the results are due to anything other than error introduced by the oscilloscope itself without a more rigorous experiment.

Re: I bought 1000 meters of wire to settle a physics debate [video]

#88

Post by Jansen312 »

formerly_proven wrote: post #37
randyrand wrote: post #28

Earlier quoted context omitted.

It’s not pedantic. EMI “teleporting” outside of wires is a real world issue that engineers deal with constantly. FCC certification is almost entirely about this phenomenon. It’s just told in a confusing controversial way.

I'm not an avid Veritasium viewer but from what I've seen this MO seems to be kinda his shtick.

Veritasium is the better teacher. The rest is just jumping on the bandwagon to grab viewerships. Think about it, back in your school days, you have an inspirational teacher that challenge or motivate you to pursue something. Rarely that teacher will spoonfed you with all information. I have many great teachers that explain well. But not a single one of them make it to the list of inspirational. I have 1-2 memorable teacher that really inspire me and they don't exactly explain things exceptionally clearly and all-in-one package. Veritasium is the kind of person that moves needles. Electroboom will be the inspired students to follow-up. The fact that he demo that wind car thing correctly and better than the specialist shows that he is the better teacher.

Re: I bought 1000 meters of wire to settle a physics debate [video]

#89

Post by afiori »

tpush wrote: post #76

So, I genuinely do not get the "controversy" over the Veritasium video. AFAIU, the entire point of the video was to show that electricity travels not through wires but via electric fields ("through the air" so to speak). To illustrate this, he sets up an experiment with parameters such that the conclusion can only mean that some electricity has traveled to the bulb before any could arrive through/around the wires. He…

In my opinion the video made a couple of mistakes, which I think ElectroBoom's response* addresses nicely.

Also its proof using the pointing vector to show the flow of energy is misleading; In the video Derek shows that the energy flows toward the lamp when the circuit is already in a stable configuration, but the point of the video is to explore what happens before the circuit reaches that configuration.

This is relevant: assume that the right half of the cable is connected to the positive pole of the battery, in a stable configuration every point of the right half of the circuit has a positive charge (creating the poynting vector field as shown in the video) while 1/c seconds after the switch was closed the wire just to the right of the lightbulb will have a negative charge (the cable near it is positively charged from the battery and so the upper cable acts as a the negative half of a capacitor) which changes the direction of the poynting vector.

In the end it felt like it was telling you that its message was that energy travels via the fields but what it actually said what that switches cause electric interference.

*https://www.youtube.com/watch?v=iph500cPK28

Re: I bought 1000 meters of wire to settle a physics debate [video]

#90

Post by foxfluff »

lmilcin wrote: post #9

Fun to introduce general population to some interesting physics but please, don't call it "settling physics debate". There is NO debate. Not physics debate, not even practical debate because that knowledge is in practical everyday use. We know signals in wires take time to propagate and I have to take this into account when I design my circuits. Things like matching lengths of traces (especially differential pairs) s…

"I have never in my life length matched the two lines of a differential pair, including at 10 GHz. Never." - Rick Hartley

https://youtu.be/QG0Apol-oj0?t=2765

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