HN Theater @HNTheaterMonth

> Anything involving the electrical energy not inside wires has no water analogue (ie the electromagnetic waves inside a transformer)

You don't even need fancy things like transformers for energy not in the wires to be important. Even a simple DC circuit consisting of a battery in series with a light bulb mostly involves an electromagnetic field to transfer energy from the battery to the light bulb, which mostly takes place outside the wires.

The function of the wires when it comes to energy transfer is to carry moving charge which creates the magnetic part of the electromagnetic field that actually carries the transferred energy.

Here's a pretty good explanation [1]. That video was from January 2019, and not controversial. Veritasium did a video on the topic in late 2021 that didn't really present things as well and ended up being quite controversial [2]. Other well-known YouTube channels such as EEVblog [3] and ElectroBOOM [4] responded.

There was also someone who bought a bunch of wire and did the experiment as described in the Veritasium video (although scaled down). That was discussed on HN and that discussion contains some very interesting links [5].

In particular the link to a talk by Rick Hartley in this subthread is very informative [6]. He talks about how most EMI problems in PCB designs are due to people not taking into account the the energy is not in the wires.

[1] https://www.youtube.com/watch?v=C7tQJ42nGno

[2] https://www.youtube.com/watch?v=bHIhgxav9LY

[3] https://www.youtube.com/watch?v=VQsoG45Y_00

[4] https://www.youtube.com/watch?v=iph500cPK28

[5] https://news.ycombinator.com/item?id=29598860

[6] https://news.ycombinator.com/item?id=29601273

⬐ gaze

The thing is that KVL and KCL hold, and KVL and KCL hold for both electrons and water. You just have to not think too deeply about what motivates the electrons to move. Current is indeed the mean velocity of carriers through some area, and voltage is mmm... well it's related to the electric field. It's just not exactly fluid pressure even though it behaves as such.

The right way to think about this if you _really_ care is a bit like the way that RF engineers think about dielectric resonators. The metal motivates the fields to be guided along pairs of conductors by the motion of charge carriers within. A metal will respond in a particular way to fields, which results in new fields, and so on and so forth in a way that results in the fields propagating along in a particular way.

A propagating pulse is a bit hard to think about but you can imagine some field configuration that results in the electrons in the metal slipping a bit, and those electrons move in a way that results in new fields which contain the new wavefront of the pulse. The electrons don't keep moving -- they move on average the distance of the mean free path and give their energy to the lattice as heat. This is why the drift velocity is just a meaningless number. The fields propagate at around c and the conductors guide them.

Reply video here: https://youtu.be/iph500cPK28

Edit: apparently too slow, sorry for the noise.

Disclaimer: I don't understand nearly enough about the physics of electricity, but this was a popular response video by ElectroBOOM that Veritasium also responded to in the comments: https://www.youtube.com/watch?v=iph500cPK28

⬐ mannykannot

To be clear, you will not find that Veritasium is wrong here (whether hilariously or otherwise); it supports the essential features of the original claims.

⬐ tsimionescu

He is extremely misleading, if not technically wrong. The Poynting vector has nothing to do with why some small amount of current is temporarily induced into the light bulb. The actual electrical energy flows along the wires (inside and out). In an unrelated phenomenon, you transmit some tiny amount of electrical power directly through the air/vacuum between the battery and the bulb. In a different configuration, or if you inserted certain kinds of reflective materials, you could block (most of) this energy from ever reaching the bulb, without any change whatsoever in the current flowing along the wires. Also, if you submerged the whole circuit (or just the space around the battery and bulb) in a dielectric material with a low speed of light (say, in a piece of rock), you would get a vastly slower and weaker current, with no effect on the current flowing through the wires.

Even the part where he explains the problem with the chain metaphor is wrong. If you actually had a mechanical chain and an engine moving it back and forth, you could extract energy from the movement of the chain either by exploiting friction (to heat up something, just like a resistor does) or by using gears that resist movement in the opposite direction (e.g. slipping the chain) to achieve movement in a single direction. There's nothing all that mysterious about how we extract energy from electricity, at least in practice.

In fact, you could even get an equivalent of the small induced curent: if you recreate his extremely long circuit with a motor instead of the battery and an extremely sensitive motion detector instead of the light bulb 1m away, you would detect some motion [1m/speed of sound in material connecting them] seconds after the motor is started, assuming you are not floating in a perfect vacuum; and then vastly higher motion after 300,000km/speed of sound in chain seconds later.

Nothing more mysterious going on with the EM field.

⬐ mannykannot

Of course, if you do different experiments, you get different outcomes - no-one is suggesting otherwise.

> Nothing more mysterious going on with the EM field.

That's precisely the point here - it all works out exactly in accordance with Maxwell's laws, via transmission line theory - see also my other reply (https://news.ycombinator.com/item?id=29934233)

⬐ tsimionescu

Touched on this in my other reply as well, but my point was that our intuitions about mechanical waves describe the electrical system decently enough - the same effects (though with significantly different magnitudes) can be seen with a mechanical equivalent of this electric circuit.

This is to be expected, since the Poynting vector is ultimately a consequence of two very basic physical laws: conservation of energy, and special relativity. Any system which obeys these two laws will have some equivalent of Poynting's vector, though of course the exact formula will be different.

Veritasium's video is deliberately constructed to obscure these facts, and to make it seem like electricity is in fact more mysterious/counter-intuitive than it actually is.

⬐ mannykannot

See my reply to your other reply: https://news.ycombinator.com/item?id=29937377

ElectroBOOM replied to this: https://youtu.be/iph500cPK28

This discussion seems to revolve around Veritasium's video explaining how elecitricty doesn't quite flow inside of power lines.

I can't help but feel that "electricity doesn't travel along the wires" is a somewhat unhelpful "well, actually" explanation that kind of misses the point. And you can tell it misses the point because you can't actually carry electricity without free electrons.

And at least in part the confusion seems to focus itself around the concept of stray capacitance, which makes it doubly confusing when you illustrate it with circuit diagrams where stray capacitance is deliberately left out. See also ElectroBOOM's rebuttal [1] where he illustrates how the situation can be explained by explicitly drawing in the stray capacitance.

[1]: https://www.youtube.com/watch?v=iph500cPK28

⬐ YetAnotherNick

This guy performed the same experiment using a km long wire and measured the voltage in oscilloscope.

https://www.youtube.com/watch?v=2Vrhk5OjBP8

⬐ raverbashing

Yes, and guess what? The bulk of the electricity takes the roundtrip time to start to flow

"Oh but what about that tiny bit!" That's capacitance. Sending "electricity" through air is not new, it's called Radio.

The veritasium video didn’t create a clear picture of what’s going on and you shouldn’t feel bad for feeling more confused after watching it

ElectroBOOM has a good response https://youtu.be/iph500cPK28

> 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).

Only that he doesn't context the video with that, But with a 'trick/googly' question. One of the reasonable constructive criticism I came across for this video is from Mehdi(ElectroBOOM)[1] where he explains why the real answer is not in the options offered by Derrick.

Personally I like the quality of Veritasium videos, but I lately feel that the barometer has shifted towards sensationalism rather than scientific education.

[1] https://www.youtube.com/watch?v=iph500cPK28

Medhi Sadaghdar (Electroboom) explains this. Medhi says the video is right but starts with a trick question. That's what the controversy is about.

https://youtu.be/iph500cPK28

You should watch Electroboom's analysis if you want the full details from an electrical engineer:

https://youtu.be/iph500cPK28

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

⬐ tigerlily

I thought it was the Poynting vector? Easy to remember because it points in the direction of power flow :)

⬐ wiml

Yup, named after English physicist John H. Poynting (1852-1914).

Controversial is fine to the extent the controversy shows people struggling toward clearer understanding and better explanations, and as long as all parties are operating in good faith (i.e. not being deliberately misleading).

Let me highly recommend Mehdi Sadaghdar’s (ElectroBOOM) excellent response video https://www.youtube.com/watch?v=iph500cPK28 which does a great job of empirically investigating and theoretically explaining the subtleties involved, in a polite, respectful, and entertaining way.

I have similarly enjoyed the exchange between Sadaghdar and Steve Mould about the physics of the “chain fountain”.

These kinds of friendly scientific “debates” show viewers (e.g. kids) a bit of how the scientific process and scientific discourse works, in a form that is more accessible and digestible than technical journal papers or history books.

Having a discussion back and forth helps to improve both viewers’ specific knowledge and viewers’ processes for comprehending and interrogating new information, so long as the median viewer actually sees some of the responses. (Someone who only ever saw the first Veritasium video probably ends up with a somewhat wrong mental model.)

⬐ QuantumG

Teaching. What a concept.

It warms my heart to see a generation of scientists, engineers and communicators attacking frontiers again.

For a while there it felt like just a few of my friends were fighting for the future and everyone else had written it off to Sci-Fi.

⬐ kongolongo

ElectroBOOM's exchange with a retired MIT professor (it was over whether or not KVL always holds) was also very polite, respectful, and entertaining and yet surprisingly the professor who must have received and exchanged feedback before having published many, many times seemed to have a meltdown over a the disagreement.

⬐ canjobear

Successful professors can get to the point where they’re no longer interacting much with people who disagree with them.

⬐ jazzyjackson

should i watch the veritasium video and then this correction or just keep my ignorant/old-fashioned way of thinking about electrons and electrons holes switching places

btw my favorite, most illuminating source of electrical knowledge is the book “There Are No Electrons: Electronics for Earthlings”

⬐ Workaccount2

The entire universe is one single immensely complex circuit. There are no conductors or insulators, just one giant RLC network. This is a perfectly valid, yet extraordinarily pedantic way of viewing electronics (unless you're one of the dark wizards of RF).

The battery in your cell phone right now is in some non-zero way also powering the lights in your room. Each keypress on your keyboard registers in the heater of your neighbors coffee machine. They're all part of the same singular universal circuit.

Veritasium just ran with this pedantic tidbit to make a flashy controversial video. Which he didn't even get fully right because like Electro pointed out, there is always non-zero current flowing in everything. The lamp never "turns on" because it always was "on".

As an electronics guy, the veritasium video just made my eyes roll.

⬐ dexwiz

We live in an electromagnetic world. You can blow minds even in educated circles when you explain that most physical forces are just electrical repulsion. Dark matter is then just matter that doesn’t interact too much with electromagnetic fields.

⬐ afiori

also the part about how alternating current should push energy and pull energy with the electrons-as-chain model given that it is perfectly possible to use alternating motion as source of energy (eg the pistons of an internal combustion engine)

⬐ Kaibeezy

Did you see his one about the 3D landscape underlying the Mandelbrot set? I’ll cut him endless slack after that mindsplosion.

https://youtu.be/ovJcsL7vyrk

⬐ impendingchange

Well, it seems the markets are behind Veritasium, right or wrong.

https://finance.yahoo.com/quote/VERI-USD/