Comments by "Lepi Doptera" (@lepidoptera9337) on "Is Veritasium Wrong About Electricity?" video.

  1. Folks, you can easily simulate this with a circuit simulation program like LTSpice. When you do, you will learn that electricity does not flow inside wires. The energy flows in the electromagnetic field outside the wires, hence the potential change at the switch will immediately start propagating along the wires at the effective speed of light along the transmission line formed by the two parallel wires, hence anything that has to do with the speed of light in vacuum is already ruled out by the existence of a dielectric between them (which is needed to keep them separated). Look up the theory of a transmission line pulser and you will have your correct answer.
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  2.  @pauladamson9459  Because in that case the electrical energy is flowing into the wire instead of along it. If wires get hot, then we aren't using them correctly. The proper use of conductors is as boundary conditions for electromagnetic fields. An ideal conductor will keep the electric and magnetic components of the em field outside of its volume. In a non-ideal conductor the field can penetrate into the conductor but it is exponentially dampened. This is called skin effect and the skin depth goes with the inverse of the square root of the frequency. For DC currents the skin depth is infinite, which means that the field has penetrated the conductor completely. In that case the Poynting vector (cross product between electric and magnetic field) is non-zero inside the conductor and some or all of the electrical energy gets deposited inside the conductor.
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  3. Yes, and the entire shebang used to be available as a commercial product that was called "cable pulser". I used to have one. They are great at making flat-top pulses in the ns-range.
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  4.  @LiveType  At 300,000 km length the lightbulb will never turn on because you don't have unobtainium as conductor. That doesn't mean that there is no signal. Of course there is... a lightbulb is just not the right detector. You are basically asking "What happens when I demonstrate my failed physics/EE education?". If you put that on the internet, I will give you the obvious answer: "You will become a troll.".
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  5.  @LiveType  Yes, you do misunderstand what is going on just as much as Veritasium does. This is a simple transmission line problem with, if you want, a mismatched load. So, basically, instead of trying to understand the real physics of it, you are merely debugging/defending a bad electrical engineering design. :-)
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  6.  @motivationmonster596  People misunderstand physics. Physics treats nature like an onion, with many layers. We can use different approximations for different layers of phenomena. Classical electrons are fine for many applications, so are quasi-static fields. And then there are some things for which they don't work. That's when we deploy Maxwell's equations, quantum mechanics and quantum field theory. If you want to build LHC, then you have to understand the latter. If all you want to do is to explain water electrolysis in 10th grade, or so, then none of that complexity is necessary. Or, as my first theory professor remarked at the beginning of his first lecture: "Ladies and gentlemen! Pay attention. Physics is the art of the approximation. If you can't deal with that notion, then there is the door. Take the path across the campus to the philosophy department. That's where they will teach you to think in absolutes. We will have none of that here.". Everybody laughed, nobody left.
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  7.  @LiveType  What was the question? Are Veritasium and you trolling? Yes. :-)
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  8. Yes, it so good that you can buy these under the name "cable pulser" commercially. I had a very old one a long time ago. I think it used a mercury switch. It made extremely clean sub-ns risetime pulses. Pulse length was controlled by attaching your own transmission line externally. If you wanted longer pulses, you just put a longer cable on. :-)
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  9.  @pauladamson9459  You are welcome.
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  10.  @Neehize  Yes, it is. The impedance of the cable is in the range of maybe 150-200Ohms. The load is maybe 1Ohm. That means the actually interesting physics (pulse propagation along a transmission line) is hidden from the casual observer. What does that tell you? It tells you that Veritasium is not good at either physics or electrical engineering. :-)
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  11.  @marijnvangeest  We don't need any electrons to make electrical energy flow. That's why we have wireless communications. That's what light does. It's the physical vacuum that transfers the energy. What the electrons do is to "tell" the physical vacuum where it should transfer the energy to. They form the boundary conditions for the energy flow. That a few electrons are flowing along the wire is just a side effect. In the case of AC they aren't even doing that. See transformers... there is no physical connection between the primary and the secondary coils.
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  12.  @motivationmonster596  You mean your WIFI doesn't work? How do you think those antennas were designed? Using angel wings and dragon feathers? :-)
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  13. That's not how electrical engineers understand electricity. :-)
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  14. It's never l/c. This is a transmission line problem. What really happens is that there is an instantaneous current flow that is V/Z_tl, where Z_tl is the transmission line impedance of roughly100-200Ohm. That will, of course, not light up a 1Ohm light bulb, but it is still the zeroth order effect. As the electric field spreads along the transmission line, the Ohmic and skin effect losses will increase until, after only a few kilometers, these losses effectively take up all of the energy that we are pumping into the line. It is entirely irrelevant how long this thing goes on after that initial lossy section.
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  15. Please look up skin effect.
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  16.  @sanjinred  Can you show me the experiment that demonstrates causality breaking? :-)
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  17. Actually, it's more like tens of um/s. Since we are dealing with AC voltages of 50/60Hz, the electrons never move further than a few um, at most. Neither do they have to. That's not their job. Their job is to confine the electromagnetic fields to the immediate volume around the wires.
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  18.  @FelonyVideos  Exactly. Six orders of magnitude are nothing between friends. It's just the difference between a stick of dynamite and a small nuclear weapon. I would have gotten a bit crabby if you had been wrong by nine orders... nobody likes a guy with a thermonuclear bomb. :-)
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  19.  @FelonyVideos  I am just making fun of what happens in physics when the exponential is wrong by a "few" units. Happens to all of us with mostly comical effect. A professor of mine used to say that you will be forgiven for being wrong by an order of magnitude. It's factors of 2 and pi that are unforgivable because then you got your calculation wrong for sure. We had lively discussions about how insecure Einstein must have felt when 8pi dropped out in general relativity. :-)
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  20. You are a genius. A YouTuber who wants to make money... who would have thunk? :-)
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  21.  @motivationmonster596  It takes more than two thoughts to understand Maxwell's equations at work, I am afraid. Sorry to say, but the cable-load impedance mismatch is about as bad as the science-YouTube mismatch in this case. :-)
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  22.  @josephchristopher6603  Exactly.
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  23.  @motivationmonster596  Electromagnetism isn't easy. It is not intuitive IMHO, not even for a classical field theory. It is certainly far too complex for high school science, but we still want people to have some understanding of electricity, which means that we have to reduce the physical reality to concepts like electrons flowing in wires. That, by the way, is not wrong, if we are interested in things like electrolysis. There we really have to count moles of electrons moving in wires. It's also not entirely wrong for static electric and magnetic fields. When it comes to dynamic fields, however, the motion of charge carriers becomes a secondary phenomenon and the motion of electromagnetic fields is best explained in the context of special relativity... which, of course, is beyond the high school level for sure.
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  24.  @motivationmonster596  Not as many as you think. A visit to a good science library should correct any false ideas about how much we actually know. There is reading material there for hundreds of lifetimes. :-)
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  25.  @motivationmonster596  You are correct, I don't need science to answer the question "Chocolate or vanilla?".
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  26.  @2adamast  Yes, you are living in the world of middle school science. In the world of PhD level physics all energy flows through the vacuum and electrons in metals are merely boundary conditions that determine what those fields look like. Look, physics can be complicated and electromagnetism is where things are transitioning from classical physics (stuff moves) to field theory (energy gets transferred by configurations of the physical vacuum). It's nobody's fault that we can't teach this properly at the middle school or even at the high school level. It's conceptually and mathematically simply too involved. It is actually so complex that even many EEs who are tasked with developing high speed electronic circuits are having difficulties with it.
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  27.  @2adamast  I don't remember saying anything else. Neither will a cable pulser. Having said that, your "event horizon" argument, while valid, gives you only a limit and it's not a precise estimate because of the dielectrics, which slow things down. It doesn't tell you anything about waveforms, either. Transmission line theory does.
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  28.  @marijnvangeest  I believe I said that we don't need moving charges for energy flow, not that either the classical theory or the quantum theory is complete without them. Both theory and experiment support that notion. What moving charges do here (and that is their only function in energy transmission) is to direct the energy to where we want it. Trust me, your power company would be more than glad to get away without having to lay thousands of kilometers of very expensive wires to get the energy to you, especially since they cause losses. As you can see in the night sky, the physical vacuum is (in a sense) completely lossless for electromagnetic radiation. It gets to us all the way from the end (i.e. the beginning) of the cosmos. :-)
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  29. @Bob Indeed. The LTSpice documentation for the transmission line will tell you that. :-)
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  30.  @indio007  Sure kid, and the Earth is flat, too. :-)
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  31. So did Veritasium. He made follow up video. Twice the YouTube income for him for trolling you with a poorly made video first and then the correction later. :-)
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  32.  @georgelionon9050  Should be on his page, no?
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  33. Energy transfer here happens at the speed of light. Most of the people here simply don't know how to analyze what both physicists and EEs call a transmission line circuit.
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  34.  @creepiona5460  You mean a plumber? OK. :-)
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  35.  @creepiona5460  Water flows in hollow pipes. Electrons have to squeeze through the lattice of a solid. That's approx. like water having to flow through sand. It does... very, very slowly. I suggest you stick to plumbing.
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  36. Except that you can not treat two parallel wires as an inductance. You have to treat them as a transmission line, instead.
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  37. I don't know why your reply doesn't show, but I agree. It's a times scale separation problem. For low frequencies the shorted transmission line acts like an inductance. For short timescales it acts like a capacitor formed by a tiny stretch of it. Between those two extremes we have to analyze it as a transmission line. And technically it's also an antenna, so a small part of the energy will be radiated to free space. That alone makes it impossible to analyze this system with any kind of closed form formula. We can only assume reasonable approximations of its behavior for certain time and frequency ranges. It's one of those problems that are easily misrepresented by the way they are being asked. There are no easy answers here. One has to go through Maxwell's equations in one form or another.
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  38. That coupling impedance is approx. 100-200Ohm (one can make it lower, but not much higher than that). That's not "incredibly small". It causes tons of problems in electronics design.
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  39.  @bobwhite137  I know it is tempting to calculate capacitance only, but this is a transmission line problem.
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  40.  @bobwhite137  A transmission line is neither a near nor a far field problem. It has two dimensions, one being the distance between the conductors and the other being the length, with the length greatly exceeding the distance.
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  41.  @bobwhite137  The thing is 300,000km long. It doesn't matter much what happens on the first meter.
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  42.  @bobwhite137  But that's not what you want to know. :-)
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  43.  @bobwhite137  If a question contains a 300,000km long structure, it's not about the behavior of the first meter of it. :-)
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  44.  @bobwhite137  Sorry to say, but you were done with your first post.
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  45.  @bobwhite137  I thought you were done? What happened? :-)
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  46. Only logarithmically, if I remember the formulas for transmission lines correctly. It's difficult to make transmission lines much over 200Ohm (the impedance of the vacuum is only 377Ohm) and getting below a few ten Ohm leads to very small gaps between linear conductors. If we want much lower impedances (for ground/power plane decoupling on PCBs) then we have to sandwich multiple layers together with thin dielectrics. At multi-GHz frequencies even that fails because the effective "circle of influence" at that frequency is an inch or less. There is an entire class of high speed PCB consultant who does nothing else than to solve this problem for people who don't understand it and who can't make high speed boards.
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  47. Yes, understanding of physics. :-)
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  48.  @passivehouseaustralia4406  Yes, that's just enough to be dangerous. Not enough to be rational. :-)
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  49.  @passivehouseaustralia4406  From one PhD in physics to another non-PhD... yes. :-)
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  50.  @passivehouseaustralia4406  Experimental high energy physics is about as real as it gets, I am afraid. I did it in the deep sea, under rock and in space, in the Northern and the Southern Hemisphere. I am sure your "real world" experience was equally rewarding. :-)
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  51.  @passivehouseaustralia4406  Yeah, that sounds good, except that it's total bullshit. That's not how Einstein got to relativity and the modern derivation is about a dozen lines of high school algebra without any need for deep thoughts about light because special relativity has absolutely nothing to do with light. :-)
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  52.  @passivehouseaustralia4406  It seems that you don't know that Galileo wrote pretty much the same thing 400 years earlier, or so. :-)
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  53.  @passivehouseaustralia4406  Science is not a series of quotes. It's a series of facts and their rational, quantitative explanation. You need to try harder. :-)
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  54.  @passivehouseaustralia4406  That all physics is relative was known experimentally at Newton's time (as I said, even Galileo gave you the correct experiments that are equivalent to Einstein's elevator) half a century before Newton, or so. It's really not my problem that you don't know the history of science and that you come to the entirely wrong conclusions about Einstein's work. :-)
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  55.  @LiveType  I take the apology and move on. :-)
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  56.  @IamGrimalkin Let me know when you are done building that 1 light year long superconducting wire. :-)
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  57.  @IamGrimalkin  Let me know when you are done building a 1 light second long superconducting cable, kid. I can sense, though, that the goal post is moving at FTL here. :-)
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  58.  @IamGrimalkin  Let me know when you got a 1m long superconducting wire working at home. :-)
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  59.  @IamGrimalkin  So, you didn't. :-)
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  60. All the electric eels in the Amazon are laughing at you, right now.
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  61.  @williamhall2691  You are right. As a physics PhD it is me who doesn't understand, not you. ;-)
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  62. Yes, you can easily calculate the total energy of the system. For a typical wire pair (distance five times wire diameter) the capacitance is on the order of 12pF/m. For 300e6m that's 3600e-12*e6=3e-3F or 3600uF. At 12 V the total stored energy is then on the order of (12V^2)*3.3e-3/2 = 0.26J. Pretty negligible for something involving a light bulb. But that's the fault of the 12V light bulb and the once-on/once-off scenario, not the fault of the transmission line. At higher frequencies and voltages they can transport enormous amounts of power.
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  63. The wires constrain where the power can flow. In free space it would have to have a dipole pattern all the way to infinity. The wires restrict it to a much smaller volume.
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  64. You are correct. The transmission line has an impedance of several tens to several hundred Ohm, depending on geometry and dielectrics. A typical light bulb has an impedance of a few Ohm, tops (could be tenths of an Ohm), i.e. it is mismatched and therefor not sensitive enough to detect what is actually going on.
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  65. You can get such a shock. The magnetic field just has to change fast enough and it has to be strong enough. The field coils of a modern MRI machine are strong enough and they are switching rapidly enough to produce induced electric fields that can be felt. If they were just a tad stronger, getting an MRI scan would quickly become a very painful affair. It simply takes high powered equipment to get to the required voltages. A small battery and a piece of wire won't do. One could probably do it with a car battery and an old transformer, if the windings are reconfigured just right. Alternatively one could try to spin a strong rare earth magnet at several thousand rpm (possibly 10,000 or more... not an easy thing to do safely, flying magnet pieces definitely hurt, even without induction).
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  66. You will have to take a few serious physics classes on the subject, I am afraid. That moving charges transport the energy is easily falsified by the sun. There are no moving charges between the sun and us, and, yet, the sun deposits enormous amounts of energy on Earth's surface.
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  67.  @camilojcastillo  And by "serious physics classes" you mean "none". OK. Say, what's the drift velocity of electrons in copper? :-)
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  68.  @camilojcastillo  If electrons were moving like a chain, then the propagation velocity of electricity would be limited by the equivalent of the speed of sound in the electron gas, which would be far from the speed of light. I don't have anything against you, either, but I would advise you to take some serious physics classes. :-)
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  69.  @camilojcastillo  Yes, that's the speed of the electromagnetic wave around the conductor. The electrons are not doing any of that. That is what they would have taught you in a serious physics class. :-) And, no, you will never see a water wave moving fast. It can't even move nearly as fast as the speed of sound is in water. That's good news for people who like to be at the beach, by the way. You don't want to be hit by water at 1500m/s. That would ruin your day... and all following days, too. :-)
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  70.  @camilojcastillo  Did you take a serious physics class, yet? :-)
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  71.  @camilojcastillo  Sounds like you are in good company. Now go and take a serious physics class. :-)
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  72. OK, "electronics engineer", that makes two wrong people right now, you and Veritasium. :-)
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  73. The entire lightbulb thing is just a distraction. The simple fact is that this is a fairly straight forward transmission line problem and physicists and EEs who can't solve this are simply incompetent. That applies to famous YouTubers. :-)
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  74. Well, voltages and resistance are important if you are talking about foolish stuff like light bulbs in that video. Veritasium simply messed up in presenting the topic poorly. He may have wanted to say one thing, but ended up saying another.
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  75.  @davewalkerden  That may be as it is, but all we are looking at here is a more or less trivial long transmission line problem. One can discuss this without any befuddlement and that is what he should have done. He didn't. He made just another bad physics video. The internet is full of them. It's a perfectly normal day.
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  76. How is that supposed to work? Your metal strip is not grounded. The current has nowhere to flow.
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  77.  @ricomajestic  With two holes in it that wires go through? That's not a Faraday cage.
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  78.  @ricomajestic  No, they don't. But if you drill a hole and you run a conductor through, then it's not a Faraday cage, anymore. :-)
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  79. What are your science teachers lying about with regards to drift velocity of electrons? It is, indeed, tiny. It just happens that energy is not being transported by the electrons. That is the actual misconception that even older EEs who are not familiar with electromagnetic fields and antenna theory are working with.
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  80.  @joinedupjon  You have still not shown any evidence that teachers are deceiving their students about the drift velocity of electrons in conductors. That electrons are moving in conductors is correct, at least if we accept that we are dealing with semi-classical electrons rather than proper quantum field theoretical ones (which we simply can't teach to anybody who didn't go trough at least three years of theoretical physics at the university level beforehand). But that's where high school has to leave it. The explanation using Maxwell's equations and full electromagnetic theory is usually second or third semester theoretical physics in university (I think I did QM before I did EM, but that depends on when professors are giving the classes at a particular physics department).
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  81.  @joinedupjon  The kids were 13? That doesn't sound like high school science. In my high school this was taught properly in 11th or 12th grade.
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  82.  @joinedupjon  Why does it not make sense? You only need the full dynamic fields approach if you want to talk about energy flow at or near the speed of light. Neither static electric or magnetic fields or even quasi-static (magnetic induction) require deep insight at that level. I am not aware of any school system that does full Maxwell equations in high school. That's university level.
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  83. It is not the magnetic field but the electromagnetic field. The energy flow is given by the Poynting vector, which is the cross product of electric and magnetic field vectors. Since the electric field points (mostly) radially away from the wire and the magnetic field is circular around the wire, the Poynting vector is (mostly) parallel to the wire. There is a small component that points into the wire... that's the heating due to Ohmic losses.
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  84. A large wire loop acts mostly like an inductor and in this case the inductance would be hundreds of Henry, if I am not mistaken. Together with the 1Ohm impedance of a typical low voltage light bulb that's an RL circuit with hundreds of seconds of time constant.
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  85. Magnetic fields changing in time are causing an electric field (just not a field that is the gradient of a scalar potential). That electric field causes charges to move, which is... a current.
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  86.  @ricomajestic  Not along the transmission line.
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  87.  @ricomajestic  As long as the transmission line is charging, there is a voltage "front" running at a fraction of the speed of light along it. It's only after it's fully charged that the voltage doesn't change and the electric and magnetic fields are constant. Having said that, even in that configuration the Poynting vector is still parallel to the wires.
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  88. It doesn't matter to his income on YouTube. :-)
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  89. And what makes you believe that QED breaks causality? :-)
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  90.  @sanjinred  So you don't know quantum mechanics. OK. But why announce it publicly on the internet? :-)
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  91.  @sanjinred  I am feeling good about that every day on the internet. You will see two major sources of bullshit on the internet: everything relating to physics and everything relating to the bible. I am playing both angles. I am, after all, a Catholic atheist physicist. :-)
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  92. Of course a measurable current flows. What in the world are you talking about? :-)
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  93.  @FelonyVideos  Since electrons are not even objects, I am perfectly happy either way. Cue the endless bullshit about the electron double slit. :-)
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  94. You can easily build this yourself with a fast mechanical switch (typically a mercury wetted reed relay is being used) and a few yards of RG-58. You need a fast oscilloscope to see what happens, though.
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  95. It's a bit complicated. The transmission line formed by the wires has an impedance of between 100 and 200 Ohm, the bulb has an impedance of roughly 1 Ohm, so the signal that propagates near the speed of light along the transmission line won't do much to light up the bulb. Replace it with a 100Ohm resistor and you got yourself a cable pulser. The resistance of the copper in the wires and the skin effect cause an exponential loss with length, so the last 299,990 km of the wire loop do not even matter. There will be no DC current left to light the bulb. :-)
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