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 sets up the parameters so that the bulb would turn on by that little electricity; but that is obviously just a visual sign, and his point is valid no matter how much electricity traveled to bulb under whatever different parameters.
It kinda feels like most people are missing the actual point of the video.
1) Slander: He claims that the way EE is taught is a "lie" but leaves out the many ways that standard EE models agree with his result.
2) Clickbait / inadequate explanation: he leaves out many details in order to make his experiment seem far more mind-blowing that it really is.*
Critique 1 can be countered by saying he is targeting a lay audience (say, they took 1 high school physics course).
Critique 2 can be countered by saying he is targeting a slightly more advanced audience who would understand those details (say, 1 or 2 college courses).
But no matter who you think he's talking to, at least one of these critiques holds.
* In particular: a) He doesn't explain how "1/c" is derived from the 1m gap. b) He portrays the electrical field as totally detached from the layout of the wires. But if you rearrange his lightsecond-long wires to be a circle, the effect won't happen. c) He leaves out the fact that this experiment works even if you cut the ends of the wires, which would change many people's intuition (think of the wires more like antennas). d) His thought experiment is actually wrong: see Electroboom's video, but basically by Derek's own parameters the light would _always_ be turned on.
I got the answer "wrong" by watching the video because I didn't consider the tiny amount of current induced in the other wire to be sufficient to turn on the light in any useful manner. If you had replaced the light with a sensitive ammeter and asked me what the first point in time there would be any measurable deflection from zero, then I would have gotten it correct.
Could have also just asked how this works, and the success rate would have gone way up (but he'd have lost all his clickbait):
https://www.amazon.com/Fluke-324-Temperature-Capacitance-Mea...
Ask bad questions, get bad answers. Nothing wrong with how physics/EE is taught.
You don’t need to use Maxwells equations or the underlying semiconductor physics equations when biasing a transistor, or calculating the output of a digital XOR gate because there are abstractions that are far simpler to use and work in just about all practical situations.
And of course those abstractions break down in thought experiments and beyond their limits in the same way that Newtons laws work up to a point and then you need Einstein.
The thing is: this is sort of true. Now, all electrical engineers are very familiar with transmission line theory, that's pretty much their bread and butter. And all EEs know that if you're not working with well-defined transmission lines (like coaxial cables), you need to use a field solver. 2D field solvers are often sufficient, but if not 3D field solvers can and will be used.
And then most of those same EEs, despite having just used a field solver which clearly shows that all the power is in the fields, which are in the dielectric space between the conductors, persist in using the mental model that electrical power moves in wires.
This isn't just a pedantic quibble. There are real, practical effects. If you're designing a PCB and you have two signal lines with overlapping fields, those signals are going to couple, which will create common mode current, which will cause an EMI problem. You can stop those signals coupling by making them reference different ground planes, which makes the fields no longer overlap. If you route a signal line from one side of a ground plane to the other, you have to provide a path for the fields to get to the other side of the ground plane (i.e. "route" the dielectric, generally with a ground via), because if you don't, they will find their own path anyway and you won't like the results.
If you persist in thinking that electrical power flows through wires, these sorts of effects are mysterious and only explicable through the magical black box that is a field solver. If, on the other hand, your mental model is that electrical power is in the fields, then -- surprise! -- the results of a field solver won't be so mysterious any more.
And if you have a more accurate mental model, if you can predict more or less how the fields will behave before looking at the results of the field solver, then that means you can design with the fields in mind, rather than just tweaking things until the field solver stops being angry at you, but not actually understanding why the design works in the end.
Don't believe me? Here's Rick Hartley, an extraordinarily experienced PCB designer: https://www.youtube.com/watch?v=QG0Apol-oj0&t=1102s
I found the responses from other EEs on youtube like Electroboom and EEVBlog disappointing. You can quibble about details of how he presented it (like, saying 1/c rather than 1m/c), but Maxwell's equations are the correct description of how electricity works, and Veritasium is absolutely correct in his core point which is that power flows outside the wires. Other models, such as lumped-element and transmission lines can suffice for many purposes but are ultimately wrong. Rather than responding towards him with hostility, perhaps they should have considered if their own mental models weren't quite as accurate as they had thought.
As a final note, the problem as presented by Veritasium can't be accurately modeled by anything less than Maxwell's equations (i.e. a field solver), but you can get most of the way with transmission line theory and tweaking it with some physical common sense. Closing the switch causes electric and magnetic fields to propagate across the gap between the switch and the light bulb, and down the two transmission lines, at the speed of light (modified by the relative permittivity). The current that will initially flow across the light bulb, once the fields reach it, can be calculated from the characteristic impedance of two parallel wires acting as a transmission line. When the signals reach the end of the transmission lines, they will "see" a short and reflect with opposite voltage; when that opposite-voltage signal reaches the switch and light bulb the transmission lines act like a short and from that point on the light-bulb receives the full current. That 1m/c delay, in particular, isn't accounted for by transmission line theory at all. The way you get that (without a field solver) is by knowing that electrical power is in the fields, which propagate at the speed of light. Since transmission line theory can't accurately model the problem in full, I think Veritasium can be forgiven for not mentioning it (especially since he was targeting a general audience).
At first order the bulk of the energy follow the wire like a train on its rails.
Sure you could put a windmill turbine one meter next to the train and the wind from the train passing will make it turn immediately, but no one would argue about that the wind carry most of the energy.
It works this way because the electrons are stuck on the wire like a train is stuck on its rails. The Electro-Magnetic field on the other hand like the wind is free to permeate space. What is important to understand is that electrons and EM-field are two-distinct things that are coupled together.
Derek's video tried to explain transmission line theory, but didn't do the experiment while making grandiose claims about a fictional setup. Kudos to alpha phoenix for doing the experiment.
Given that Derek recently created multiple "debate" videos, and that he is more interested in the way to teach Science and how to reach a lot of people than by Science itself, it feels like he probably has engineered this controversy himself for views as a meta-experiment.
A lot of video responses from unknown youtubers show a better understanding than the original. For example you can see a numerical simulation of the electro magnetic fields (with Ansys) https://youtu.be/aqBDFO1bEs8?t=364 that show how electricity move (the separation distance between the wire there is only a few centimeters).
The problem though is interesting if you try to understand how exactly the energy transfer is happening : Is it capacitive coupling, Is it inductive coupling, Is it EM radiation ? Which one exactly is the dominant term ? Where exactly are the electrons ? How are the electrons interacting with the field ? How can you shield it to isolate and show the various effects (magnetic shielding, electrical shielding) ?
1) To get the result presented heavily depends on the experimental setup and this appears to be hand-waved away (or for the cynics: deliberately obscured) as it would detract from the impact of the video.
2) The definition of "ON" in the video is not what anybody would reasonably define as "ON". This is not discussed in the video therefore potentially comes of as deceptive.
As an electronic engineer I actually initially found the video confusing. I wasn't familiar with Veritasium before and I will admit my initial visceral reaction was "Oh he's just one of THOSE YouTube's and needs his clicks".
It wasn't until I went back through to understand Veritasium's unspoken assumptions, simplifications and a couple of medium mistakes that I could say: yes this is technically correct.
Personally I think with some better choice of wording the pitchforks wouldn't have come out as they have.
Edit: Added word for clarity.
The definition of "ON" is exactly the main controversy with this and not a subtle detail.
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.
Derek would not have written tweets like this one, if his video had been more direct about what he was talking about:
https://twitter.com/veritasium/status/1462115954775654405
"Basically yes - you can think of it like two antennas"
I think the key part of the controversy is the word "some".
In the original Veritasium video it pretty strongly implies that enough energy to light the bulb, i.e. virtually all the electricity, is traveling instantaneously a short distance rather than "through" the wire.
A big part of that video is to essentially say you're wrong if you understand electrons moving through the wire as how electricity works.
The video posted here tells a different story which is essentially that the mental model of electrons flowing isn't that far off, but there is a bit of nuance when you take into account fields.
This is sort of a persistent problem with "edutainment". I generally enjoy Veritasium, but this is clearly a case where the education component is weakened in order to increase the "wow!" factor of the video.
in direct current, how does charge move from one terminal to another if it's not carried by electrons (which often act as waves)?
I'm having trouble understanding what is even being claimed. Electrons are moving, without the movement of the electrons there is no electricity travel, without the wires there is no flow of electrons, so what does it mean to say that electricity doesn't travel through wires?
Is the claim just that the electricity, by way of fields, travels at a rate much faster than the electrons themselves are traveling? That seems like a reasonable claim. But "electricity doesn't travel through wires" seems rather suspect.
Now, if you follow it carefully, it makes a different point, that is actually correct: it actually claims that some energy travels this way, since the electric field is not strictly bound to the wires, some part of it radiates out.
What the video is sorely missing is a discussion of the intensity of that field, which is going to be extremely low even 1m away from the wires, for typical batteries. These effects are absolutely important though in high power cases, where even a small fraction of the energy carried along the wire leaking to nearby wires still means you can actually light a lightbulb (or burn many other things).
The point is that the energy goes through the field, not through the wires.
In your example, the Poynting vector would go towards the resistor, where the energy is turned into heat.
I think it’s specifically that the energy flux has a well-defined vector at every point in an electromagnetic field, and those vectors do not point along the wires.
Thanks, For me this is the best comment in this thread.
I love his videos, but the reason most people are missing the point is because he only obliquely hits the point. The title and thumb are the clickbaitiest he's ever done, and the content does a wide end-run around the facts, rather than tackling them head on. This is also why there are so many rebuttal videos that agree with him and explain it more clearly: he failed to clearly state his argument/explanation. The circumlocutious explanation does little to edify the audience or clarify the concept.
That's the bit where he's factually wrong. He's made this illogical world where the tiny amounts of electricity in field lines well outside the wire trigger the lamp but the leakage current and other sources of current don't. If you're going to be pedantic about something you have to be pedantic about the whole thing, damn it. Veritasium's video is like saying "water flowing through pipes is a LIE" because some molecules of water make it through the various seals and diffuse across the outer surface of the pipe.
> Veritasium's video is like saying "water flowing through pipes is a LIE" because some molecules of water make it through the various seals and diffuse across the outer surface of the pipe.
Not at all.
“What’s the point of the wire?”
- it’s not the length of the wire, it’s the distance between power source and consume that determines how fast power travels (how does power “know” where to go, if not following the wire?)
- since power travels outside the wire, it should be okay not to plug in the power consumer.
I’m pretty sure that’s completely and utterly wrong, but I don’t know what he is trying to say. So the video creates more confusion than it clears up.
> It kinda feels like most people are missing the actual point of the video.
Which raises an age old philosophical question about communication: who’s at fault for the misunderstanding: The sender or the receiver?
I’d say it’s a bad video because it is from a trusted source of science and most people misunderstand it.
I think this is the most fascinating debate on social media currently.
Nothing (except forgetting the units of meters) he said is wrong. It's just a bit uncharacteristic that the video didn't match the initial quiz, and it ignores some of the most interesting bits of the behavior. But it wasn't targeted at EEs who are already familiar with the "simple" transmission line behavior, it was targeted at people who haven't ever learned or dealt with that. So the steady-state behavior would have distracted from the focus of the video IMO.
That's the controversy. It's great that he found a fun way to explain transmission theory and how wires are effectively antennas, but he's taking the same thing he initially calls out (how the general understanding most of us have is a lie) and making it even worse in another direction.
This also means that the "misconception" claim is really just click-bait and really there was never any misconception.
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.
Actually for air, according to this source [2], the velocity factor is 0.999707085823853610892 c.
[1] https://lowpowerlab.com/guide/rf-best-practices/velocity-fac...
We're going to see more and more this type of video. Instead of the thumbnail and title of the video being extremely controversial to attract views, the thesis of the video will be controversial to create endless online debate.
https://en.wikipedia.org/wiki/Skin_effect
I hope one of the outcomes of this discussion is that someone will tackle explaining how AC power gets from source to load, and what 'earth grounds' have to do with that ... and WHY. The usual hand-wavy 'simple' discussions leave out WAY too much.
could it not also be that some of these students didn't actually learn what was being taught, and just squeaked by with minimum grades to not have to take it again?
a) it's pretty trivial to do (I did it myself when the video was new because dangit a physicist kept sayin' I was wrong on the internet and that's UNACCEPTABLE)
b) there's a PDF in the description where one of the EE profs he asked did and gets exactly the same results as everyone else and also shows how easy it is to predict behavior of the experiment using line theory.
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 would be a much more limited version of the experiment. The promised followups also cover exactly what I'd like to see tried next.
Z ≈ 276Ω * log10(2 * separation / diameter)
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) so that critical signals take same time to propagate or matching length of trace and return to improve signal integrity are staple for anybody that is working on anything over couple hundred megahertz.
All of this only because it takes time for signal to actually travel through the length of the wire.
But if you don't want it to broadcast noise like crazy you want it tight and matched as much as possible.
The value of differential pair comes from the fact that they have constant common component. That only works if both components aren't shifted in time. If that happens, you will get strong common signal and say bye to nice quiet differential pair.
I'm guessing you never checked the comment section.
Try to find a post on HN with a lot of upvotes and comments where everybody would agree on something.
If you want to know if there is "physics debate" ask people who know physics, not commenters on Youtube or HN.
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.)
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.
I also wonder what would happen if, instead of a setup like this:
┏───────light────────┓
┕──────battery───────┛
┏──────────────light─┓
┃ ┃
┃ ┃
┃ ┃
┃ ┃
┃ ┃
┃ ┃
┃ ┃
┃ ┃
┃ ┃
┕─battery────────────┛
Put another way, the main reason this effect is observable in the way shown in the video is because the light and battery, and the wires between them, are so close together. Move them further away, and, per the inverse square law, you'll start seeing a much lower induced current-- the effect may still be there, but it won't be measurable over the noise floor of the experiment setup.
What happens when they are not close enough for any meaningful electric field interaction?
The other issue with the Veritasium "setup" was that he specified that the wires had no resistance. That being the case the RC time constant would be 0 and thus you wouldn't see that initial charging of the capacitance (and associated current flow) because it would happen instantaneously under those assumptions.
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 problem.
The thought experiment he proposed was just a hook to keep people interested - and it certainly did the job. Because it is a popular internet video by a popular YouTuber, however, the entire scientific community made it a mission to nitpick every detail of that experiment and show that the conclusion wasn't 100% accurate without a bunch of caveats. Which is fine, I guess, but also missing the point of the whole thing.
You can't just say "there's electricity at the light bulb nearly immediately! (oh by the way it's not very much electricity but I'm not going to explain why or even how much less, and it's probably not even enough to turn on an LED but I'm not even going to mention that)" and then get pissy when people are like "???!??!?!" It's pretty blatantly deliberately misleading and confusing in order to stir up exactly this controversy.
Especially since the effects he's describing are probably (as mentioned in this video) because of capacitance, and are completely dependent on the 1m distance between the wires across the entire span, a constraint he mentions basically once and then never again, and never says explicitly that it's related to the effect.
This video and electroboom's videos are far more educational, and more importantly don't leave you hanging with a bunch of new questions with no resources provided to answer them.
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.
Also, for such a pedantic video his field lines were wrong.
Well played though that the world thinks he knew his wrongness would spur debate.
Speaks to his earned credibility, but not to his infallibility.
Which was exactly his point— It's called "engagement".
Take 1km of wire, a resistor lightbulb, and a power source. Connect oscilliscope around power source. Flip switch.
For 1 light-speed delay, you actually see current going across the lightbulb! After the speed of light delay, current starts flowing normally as expected. (Why? How? Is this spooky action at a distance?)
You're actually seeing cross-talk between the wires where the build-up of electrons on the high side actually moves electrons on the (spatially) adjacent side of the loop!
Then to really complete the puzzle, sever the end of the wire. You still see the exact same behavior up to the speed-of-light time! (Which, how could you not! You need to wait a speed-of-light delay to _discover_ that the wire was severed, so you MUST see the exact same behavior.)
Therefore if the wire is either intact or broken at the far end, over a 500m distance the first 1.6us of measurement looks exactly the same.
[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.
Yes, very long wires behave like capacitors/antennas and transmit a certain amount of transient power instantly by coupling, but most useful energy is transferred after the speed of light delay, when steady state is achieved.
Nonetheless, by carefully selecting the AC frequency and the physical configuration of the lines, you can create a situation where most energy is transferred nearly instantly by the electromagnetic field and the far ends of the line are more or less irrelevant. So you obtain the Veritasium effect, but it's a very particular arrangement, not the general case.
Physics Explained is great physics channel that doesn't shy away from math, with derivations of many fundamental equations. His most recent one deriving the Chandrasekhar limit on white dwarf stars from relatively basic physics is great!
The Efficient Engineer is a really good one for clear concise explanations of mechanical engineering principles.
Of course if you take it literally - superconducting wires, car battery, 12 V light bulb - then it's very likely that the suggested answer is not even technically correct, because the initial pulse amplitude as seen by the lamp is simply too low to light the bulb up. If you take it less literally and match the "light bulb" impedance more or less to the transmission line impedance (~1 kΩ or so in the experiment with the suggested wire spacing and assuming "reasonably thing" wires), then you're getting much closer to the answer he is suggesting.
This steady state of motion is like "drift current", whereas the initial ripple of couplings clattering together an initiating the motion is like the electric field propagating through the circuit.
Of course, EE's know about drift current, transmission line behavior and other topics.
To get the 1m/c s answer, for your example you would have to add a seismograph to the opposite end of the train track - while the cart at that far end will only start moving once the ripple goes around the whole track, the seismograph will pick up the movement almost instantly, since the movement of the initial cart will send waves through the earth directly, not following the tracks.
For a transmission line i.e. one limited by distributed inductance and capacitance, the standard practice is to drive a powerful transient into one end, which then travels along the wire, switching any receivers along the way, and then absorb it in a termination resistor at the other end so it doesn't bounce back and glitch the receivers on the return trip. Again you have to consider an actual traveling wave; there's no such thing as "instant" on a wire of any length.
"Admiral Grace Hopper Explains the Nanosecond" is a good illustration of this (segment is only 2m):
* https://www.youtube.com/watch?v=9eyFDBPk4Yw
* https://en.wikipedia.org/wiki/Grace_Hopper
Full lecture:
Since glass[1] has an refractive index of roughly 1.5, speed of light in a glass fiber is roughly 2/3 foot per nanosecond, so you actually have 180 bits in transit.
[1]: at least most kinds of glass used in optical fibers and windows, at the wavelenths typically used in optical communications, which tends to be roughly in the range of 800nm to 1500nm
Things like Ohm’s law are great tools for understanding circuits. However, the underlying forces that derive these equations are a bit lower level, and relate to charged particles creating electric fields. Every electron flowing is because there’s a net force on it, coming from an electric field caused by other electrons, protons, or magnetic interactions.
Electric fields are kind of hairy to use directly, and a much more easy-to-use concept is voltage. Voltage abstracts the field concept away, and tells you about how much energy will be expended moving charge around.
Turn a circuit on, what happens isn’t that the whole circuit works in lock step. First some charges near the power source will move, inducing new fields that propagate as a wave.
Bro, if this is your product, it seems fucking cool, dude. Told my buddy and I'm going to request an invitation too.
Anyone care to help me out? Maybe that just isn't much?
You can intuit it by knowing Avogadro's constant is 6e23.
So 1e-5 mol, 1 mol of (atomic) Copper is 63g, so that's 6e-4g of copper. Density of copper is 9g/cm3 so let's say 1e-4 cm3 = 1e-1 mm3 = 0.1 cubic mm of copper.
So one amp in a copper wire is equivalent to 0.1 cubic mm of that wire's electrons flowing out each second. I'd say that's "barely moving".
(very roughly)
Just to validate then, these barely moving electrons will create a field that induces a current on the electrons on the other side of the wire that is 1m away, which would turn on the bulb, that if the lightbulb was an ideal current detector that ignores all other sources of electric fields?
Fortunately Gallifrey Prime has easy returns. ;-)
The long wires act as transmission lines with an easily calculated impedance of ~1 kΩ. When you close the switch, you generate a pulse - a very broadband AC signal - which starts to travel around the circuit. While the pulse is traveling in the line, the line's inputs see the line impedance. So you get the car battery in series with 2x the line impedance in series with the impedance of the light bulb. This directly tells you the amplitude you're going to see near-instantly at the light bulb. Light bulbs are usually low-impedance (e.g. a 10 W, 12 V light has a hot resistance of around 14 Ω), so you're only going to see a tiny pulse on the light bulb. After the pulse has traveled the length of the line and back the impedance seen across the line inputs is the short at the end in series with the conductors resistance of the line itself; in a heavily mismatched setup you're going to see some more reflections going back and forth, this causes the stair-stepped rise over multiple bounces when you do this experiment with "realistic" values.
It's basically a slightly unconventional TDR - time-domain reflectometry - setup.