4 ms·

I take your point that Veritasium himself did not analyze the scenario as a transmission line, and he would probably have been clearer if he had done so. Also,

I take your point that Veritasium himself did not analyze the scenario as a transmission line, and he would probably have been clearer if he had done so. Also, in several places here, you say that you took him as saying this or that, and if that is how you (and probably others) saw it, then he could have been clearer by anticipating and explicitly addressing those concerns. In addition, it was probably a mistake to present it as an issue of whether a bulb of the sort he showed would light up, given how many people got distracted by that detail. Therefore, I accept that the video could have been clearer, but I still see no reason at all to accuse Veritasium of being deliberately misleading. On the other hand, the thing about the chain analogy is that it is not "nonsense", as you put it, to point out that it is not the complete picture in general, it is not an "exact" intuition, and, most relevantly here, that it completely fails to explain what happens in this case in the period of interest, prior to the arrival of the reflected wave back to the origin and the establishment of a steady state. Furthermore, one can not get the correct answers - or the correct intuitions, for that matter - from any model that assumes the energy flows only where the charges are moving (this was a roadblock in understanding electromagnetism which was broken by Maxwell introducing the displacement current.) Therefore, Veritasium had good pedagogical reasons for saying that the chain model is not accurate and for introducing the Poynting vector. As I pointed out in my previous post, your previous post consisted of a series of points in which you were saying, in effect, that Veritasium was correct, and if you want to reverse course on that now, I think you owe us an explanation of how the chain model explains what happens in the first second after the switch is turned on.

tsimionescu 5y ago
> As I pointed out in my previous post, your previous post consisted of a series of points in which you were saying, in effect, that Veritasium was correct, and if you want to reverse course on that now, I think you owe us an explanation of how the chain model explains what happens in the first second after the switch is turned on. It depends what level of detail you want to explain. The chain model explains pretty well what happens in the steady state of the circuit, as long as we take the chain links to represent EM waves and not actual electrons. It also suggests that the motor starting to move the chain will cause some amount of motion to happen at the middle point by radiating mechanical waves through the air/ground. This explanation is actually equivalent to the amount of detail that can be gleaned from Veritassium's video - since his explanation also doesn't give (a) any quantitative description nor (b) any idea of what kind of motion/energy is being transmitted. Of course, the chain analogy is nowhere near good enough compared to the transmission line explanation. Apart from the quantitive issue, the biggest weakness is that it predicts some kind of random motion, whereas the actual transmission line model predicts a current in the same direction as the final wore current. A closer mechanical analogy which might actually have the necessary features (though definitely highly dampened) would be using a loud speaker and a water pipe. The loudspeaker will send a mechanical wave through the water pipe which will travel at the speed of sound through water, whereas water molecules will move in the same direction but much slower, similar to the real electron movement. Secondly, the sound waves will also travel through air and quickly reach the mid point of the pipe, and here they should actually cause a smaller sound wave to start traveling through the pipe from that point as well, in the same direction that the final wave will travel. The magnitude of the effect will be much smaller than in the EM case, but the other characteristics should be similar. In fact, this sound-wave-in-water-pipe model would also predict the right phenomenon if you had two close parallel unconnected pipes, and were sending a sound wave through one of them - the sound wave would be transmitted across the gap and through the second pipe as well, even if the source were far away. The chain model might predict something similar here, but at a rate that is below our normal ability to notice, and thus outside our regular intuition.
- mannykannot 5y ago
  > It depends what level of detail you want to explain... To be clear, the issue we are seeking to explain is the first second or so of the thought experiment. [1] > The chain model explains pretty well what happens in the steady state of the circuit, as long as we take the chain links to represent EM waves and not actual electrons. But that isn't the chain model that you are complaining Verisatium is deprecating! You are implicitly agreeing with him by adding the caveat that I have emphasized! > It also suggests that the motor starting to move the chain will cause some amount of motion to happen at the middle point by radiating mechanical waves through the air/ground. This is getting increasingly Rube Goldberg with every iteration! > This explanation is actually equivalent to the amount of detail that can be gleaned from Veritassium's video... This is not an explanation, it is at best an attempt at an analogy. > ...since his explanation also doesn't give (a) any quantitative description nor (b) any idea of what kind of motion/energy is being transmitted. As hand-wavy as his explanation is, it does actually talk about things that can be found in EM theory. On the other hand, while you have hinted at a new, improved chain model that incorporates EM waves, you have not actually rolled it out to explain what happens in that first second in those terms, and I have no idea how your rattling-chains analogy is supposed to get the job done. >[more of the same, but with pipes and loudspeakers!] > In fact, this sound-wave-in-water-pipe model would also predict the right phenomenon if you had two close parallel unconnected pipes, and were sending a sound wave through one of them... It does? Please explain, because I have no idea how you think that can be achieved. In my previous post, I acknowledged your point that Veritasium could have been clearer, but I do not think this is a step in that direction. [1] More generally, wherever the ratio of the characteristic distances to the characteristic times is multiples of c, which is commonplace in RF.
  - tsimionescu 5y ago
    I thought I had explained this in an earlier post as well, but let's go into more detail with the chain analogy. First of all, our experiment looks like this: we have a length of chain inside a tube arranged into a rectangle with 2 short 1m sides and two much longer sides (hundreds of km?). The longer sides of the rectangle are placed top and bottom. At the mid-point of the bottom side we have a motor that can pull the chain. At the midpoint of the other end, we have a piezoelectric generator standing very close to the chain. Once we turn the motor on, it will immediately start moving the chain at the near end, but it will take some long amount of time until the links near the piezoelectric start getting pulled. However, the movement of the links near the motor will create sound waves that will start traveling radially outwards from each point, starting with the position of the motor itself. The piezoelectric generator will start being rattled by these sound waves and producing a very small current after a duration of 1m / speed of sound in connecting medium (equivalent to 1/c s). After length of chain / speed of chain seconds pass (equivalent to 1s), the piezoelectric generator will start being rattled by the movement of the chain links near it as well, which has a much higher value. This experiment models (a) how the engine transmits energy to a distant system regardless of how the chain is moving, and (b) what happens in the initial "1s" before the steady state. If we switched from one-way movement of the chain (DC) to alternative movement (AC), the setup also predicts (c) that the energy keeps flowing from engine to piezoelectric generator, even if the chain links are no longer moving along the whole length of the chain. It also shows that (d) energy is not in the chain links themselves, but in the sound waves they give off. Note that I used a piezoelectric generator as the first thing that came to mind that does useful work while rattling in any direction, but the electrical component is not really important. > > In fact, this sound-wave-in-water-pipe model would also predict the right phenomenon if you had two close parallel unconnected pipes, and were sending a sound wave through one of them... > It does? Please explain, because I have no idea how you think that can be achieved. If a water pipe A is carrying a sound wave, that sound wave will not be confined to the pipe itself, it will also propagate outwards radially from each segment of pipe. If there is another pipe, the sound waves from the original pipe will start vibrating the water in the second pipe, which will in turn cause other molecules of water to start vibrating and thus carrying the sound wave along the second pipe as well. Of course, in practice the effect will be significantly dampened, but it should happen. The one thing that these mechanical wave models are completely incapable of explaining, and the thing that Maxwell was able to, is why and how these effects keep happening with electricity even in a perfect vacuum. Modelling EM waves as mechanical waves actually works pretty well until you remove the medium and they keep propagating.

tsimionescu 5y ago

> As I pointed out in my previous post, your previous post consisted of a series of points in which you were saying, in effect, that Veritasium was correct, and if you want to reverse course on that now, I think you owe us an explanation of how the chain model explains what happens in the first second after the switch is turned on. It depends what level of detail you want to explain. The chain model explains pretty well what happens in the steady state of the circuit, as long as we take the chain links to represent EM waves and not actual electrons. It also suggests that the motor starting to move the chain will cause some amount of motion to happen at the middle point by radiating mechanical waves through the air/ground. This explanation is actually equivalent to the amount of detail that can be gleaned from Veritassium's video - since his explanation also doesn't give (a) any quantitative description nor (b) any idea of what kind of motion/energy is being transmitted. Of course, the chain analogy is nowhere near good enough compared to the transmission line explanation. Apart from the quantitive issue, the biggest weakness is that it predicts some kind of random motion, whereas the actual transmission line model predicts a current in the same direction as the final wore current. A closer mechanical analogy which might actually have the necessary features (though definitely highly dampened) would be using a loud speaker and a water pipe. The loudspeaker will send a mechanical wave through the water pipe which will travel at the speed of sound through water, whereas water molecules will move in the same direction but much slower, similar to the real electron movement. Secondly, the sound waves will also travel through air and quickly reach the mid point of the pipe, and here they should actually cause a smaller sound wave to start traveling through the pipe from that point as well, in the same direction that the final wave will travel. The magnitude of the effect will be much smaller than in the EM case, but the other characteristics should be similar. In fact, this sound-wave-in-water-pipe model would also predict the right phenomenon if you had two close parallel unconnected pipes, and were sending a sound wave through one of them - the sound wave would be transmitted across the gap and through the second pipe as well, even if the source were far away. The chain model might predict something similar here, but at a rate that is below our normal ability to notice, and thus outside our regular intuition.

mannykannot 5y ago
> It depends what level of detail you want to explain... To be clear, the issue we are seeking to explain is the first second or so of the thought experiment. [1] > The chain model explains pretty well what happens in the steady state of the circuit, as long as we take the chain links to represent EM waves and not actual electrons. But that isn't the chain model that you are complaining Verisatium is deprecating! You are implicitly agreeing with him by adding the caveat that I have emphasized! > It also suggests that the motor starting to move the chain will cause some amount of motion to happen at the middle point by radiating mechanical waves through the air/ground. This is getting increasingly Rube Goldberg with every iteration! > This explanation is actually equivalent to the amount of detail that can be gleaned from Veritassium's video... This is not an explanation, it is at best an attempt at an analogy. > ...since his explanation also doesn't give (a) any quantitative description nor (b) any idea of what kind of motion/energy is being transmitted. As hand-wavy as his explanation is, it does actually talk about things that can be found in EM theory. On the other hand, while you have hinted at a new, improved chain model that incorporates EM waves, you have not actually rolled it out to explain what happens in that first second in those terms, and I have no idea how your rattling-chains analogy is supposed to get the job done. >[more of the same, but with pipes and loudspeakers!] > In fact, this sound-wave-in-water-pipe model would also predict the right phenomenon if you had two close parallel unconnected pipes, and were sending a sound wave through one of them... It does? Please explain, because I have no idea how you think that can be achieved. In my previous post, I acknowledged your point that Veritasium could have been clearer, but I do not think this is a step in that direction. [1] More generally, wherever the ratio of the characteristic distances to the characteristic times is multiples of c, which is commonplace in RF.
- tsimionescu 5y ago
  I thought I had explained this in an earlier post as well, but let's go into more detail with the chain analogy. First of all, our experiment looks like this: we have a length of chain inside a tube arranged into a rectangle with 2 short 1m sides and two much longer sides (hundreds of km?). The longer sides of the rectangle are placed top and bottom. At the mid-point of the bottom side we have a motor that can pull the chain. At the midpoint of the other end, we have a piezoelectric generator standing very close to the chain. Once we turn the motor on, it will immediately start moving the chain at the near end, but it will take some long amount of time until the links near the piezoelectric start getting pulled. However, the movement of the links near the motor will create sound waves that will start traveling radially outwards from each point, starting with the position of the motor itself. The piezoelectric generator will start being rattled by these sound waves and producing a very small current after a duration of 1m / speed of sound in connecting medium (equivalent to 1/c s). After length of chain / speed of chain seconds pass (equivalent to 1s), the piezoelectric generator will start being rattled by the movement of the chain links near it as well, which has a much higher value. This experiment models (a) how the engine transmits energy to a distant system regardless of how the chain is moving, and (b) what happens in the initial "1s" before the steady state. If we switched from one-way movement of the chain (DC) to alternative movement (AC), the setup also predicts (c) that the energy keeps flowing from engine to piezoelectric generator, even if the chain links are no longer moving along the whole length of the chain. It also shows that (d) energy is not in the chain links themselves, but in the sound waves they give off. Note that I used a piezoelectric generator as the first thing that came to mind that does useful work while rattling in any direction, but the electrical component is not really important. > > In fact, this sound-wave-in-water-pipe model would also predict the right phenomenon if you had two close parallel unconnected pipes, and were sending a sound wave through one of them... > It does? Please explain, because I have no idea how you think that can be achieved. If a water pipe A is carrying a sound wave, that sound wave will not be confined to the pipe itself, it will also propagate outwards radially from each segment of pipe. If there is another pipe, the sound waves from the original pipe will start vibrating the water in the second pipe, which will in turn cause other molecules of water to start vibrating and thus carrying the sound wave along the second pipe as well. Of course, in practice the effect will be significantly dampened, but it should happen. The one thing that these mechanical wave models are completely incapable of explaining, and the thing that Maxwell was able to, is why and how these effects keep happening with electricity even in a perfect vacuum. Modelling EM waves as mechanical waves actually works pretty well until you remove the medium and they keep propagating.