11 ms·
How do electrons find the “path of least resistance”? [video]
- sister 3y agoI hope loose your sense of wonder...never settle for path of least resistance... And I hope you still feel small as you stand beside the ocean ..when ever one door closes I hope one more opens I hope you get your fill to eat but always keep that hunger .. ps dance in the reign....challenge has made to the finish line ilevennif I did not pass go. .
- imtringued 3y agoThey take all paths weighted by resistance.
- xracy 3y agoI feel like you just saved me 22m
- version_five 3y agoIt's funny how we used to say "a picture is worth a thousand words", and now a YouTube video is worth about five words.
- GaggiX 3y agoTo be honest the video OP linked is really good at teaching about electricity if you don't know much about it (and create a useful mental model).
- marcosdumay 3y agoFrom the amount of people confused here, I'm doubting this. It is very interesting. But that doesn't make it good at teaching.
- mrguyorama 3y agoHalf of HN would be confused about a ham sandwich while confidently declaring the teacher wrong.
- kccqzy 3y agoThe right picture is worth a thousand words. The wrong 39600 pictures (22 minutes x 60 x 30 fps) are worth a lot fewer words.
- mattigames 3y agoWhat have you done? Now we need to rewrite them all! "The right bird in the hand of worth more than 2 right ones in the bush"
- marcosdumay 3y agoOh, man, if you don't think the difference is important it's because you never had the wrong bird on your hands.
- FridayoLeary 3y agoYou can also say that one forum discussion is worth a dozen blog articles. SEO ruins the internet.
- NotYourLawyer 3y agoNah it’s a good video. Solid change in general.
- NotYourLawyer 3y ago*channel
- deleted 3y ago[deleted]
- KRAKRISMOTT 3y agoWith the path integral being an analogue computer.
- beerandt 3y agoThe same way (well, similar way) water flows through pipes or otherwise. How does water "solve" a maze to an open tap?
- sfifs 3y agoThat's analogy is not really correct. Nor is the one in the video. With electrons, or light for that matter you're dealing with wave particle duality and the appearance of "shortest path" is a result of the particle's wave nature. Prof Morales did a good explanatory series in Ars https://www.google.com/amp/s/arstechnica.com/science/2021/01/the-curious-observers-guide-to-quantum-mechanics/amp/ https://www.google.com/amp/s/arstechnica.com/science/2021/01... Water doesn't actually "solve" a maze either https://youtu.be/81ebWToAnvA https://youtu.be/81ebWToAnvA
- beerandt 3y agoDepends on how you set up the analogy, but sure it's not perfect. And I put "solve" in quotes precisely because it does no such thing. But a water molecule interacting with pressure gradients and waves is about the best eli5 or even eli18 that I've seen, with both particle and wave representations. But maybe that's just because I'm a hydraulics engineer and "get it."
- version_five 3y agoYour analogy is fine for a classical treatment of electricity. At some quantum level I assume it's also wrong for water, but that's irrelevant.
- beerandt 3y agoYea, but we're talking about a 22 min video vs a 2 sentence explainer to grasp the very basics of a concept here. I love to argue the technical stuff as much as anyone, but the underappreciated aspect and skill of any engineering is eyeballing cost/benefit of any expenditure. Be it sizing elements of finite analysis, or sizing an analogy.
- function_seven 3y agoThis begs the question the video is trying to answer. Imagine you have no experience or knowledge of what electricity is or how it works. Then you learn the bare basics. You might have this same question, "how does it 'know' which path has the least resistance?" The pepper demonstration in the video is a good analogy to show how the resistance information of every possible path (or, really, stub) is "back-propagated" to the branching point. No, it's not a perfect description of what is really going on, but I dare say there's no such thing. Just better and better models. If I have a wire that connects from (+) to (-) on a battery, and a dozen wires that branch off of (-) and go nowhere, how does the current "know" not to waste time trying each of those stubs? This video explains that.
- 11101010001100 3y agoit doesn't know. it 'samples' or whatever inadequate word you wish to use.
- ShamelessC 3y ago[flagged]
- Dylan16807 3y ago> This begs the question the video is trying to answer. Imagine you have no experience or knowledge of what electricity is or how it works. Then you learn the bare basics. You might have this same question, "how does it 'know' which path has the least resistance?" You're still saying "path of least resistance" though. A very important part of the answer is that it doesn't find it. All paths carry electricity. So "take all paths" isn't begging the question, it's correcting the question, and "weighted by resistance" isn't begging the question, it's giving a pretty easy answer to anyone that understands the concept of "resistance" in a non-electrical sense that some paths let things through more easily than others. And if you have a bunch of stubs, the electricity does go onto them. It just gets stuck at the end.
- mfringel 3y ago
- hgsgm 3y agoIt's even simpler if you look at parallel resistors by their conductance (more paths), and series resistors by their resistance (steeper path). As usual, more symmetrical math makes the engineering less mysterious.
- markjspivey 3y agoelectrons don’t, electricity does .
- jonny_eh 3y agoThis same youtuber made a video about that: https://www.youtube.com/watch?v=2Vrhk5OjBP8 https://www.youtube.com/watch?v=2Vrhk5OjBP8
- jagrsw 3y agoThe video is interesting, but I suspect, that the author is making some subtle errors at places. Tho I'm not 100% sure, last time I analyzed those subject was at BsC/MsC courses at my uni. E.g. he says something to the tune of electrons take a few ns. running around, and then settle down in the maze. IIRC electron flow in a medium is relatively slow, something on the order of centimeters per second. So it's not electrons which settle some potentials by moving quickly, but the electric potential finds its equilibrium. And it finds its equlibrium by electrons exchanging virtual photons (carries of electromagnetic force)?
- bertil 3y agoThe author has a fascinating video (part of a wider effort of many science YouTubers) that tries to clarify all that. https://www.youtube.com/watch?v=2Vrhk5OjBP8 https://www.youtube.com/watch?v=2Vrhk5OjBP8 I’m actually not sure if that makes his explanation more accurate because it’s informed by that, or more regrettably forced metaphor. But the whole series of videos from different creators is worth watching if you want to understand the whole “electrons are moving” thing.
- dekhn 3y agothe drift speed of electrons in a conductor is, as you say, low, while the fluctuations of the wave travel at near the speed of light, and electrons can be accelerated to near light-speed but I don't think that happens in normal signal transfers.
- Jun8 3y agoHere's a good Physics SE answer that addresses this point. The "electrons move slowly in a wire" is a hypercorrection, similar to "light slows down is glass": https://physics.stackexchange.com/a/13568 https://physics.stackexchange.com/a/13568.
- pishpash 3y agoParent didn't say electrons move slowly. Parent said electron flow is slow which is true. The article tries to say that in that average there are fast-moving parts and slow-moving parts. Fine.
- Animats 3y agoSummary: "It's like a whole bunch of stagnant lakes connected to the same river".
- bitL 3y agoCan you solve arbitrary traveling salesman problem with that? There is only a polynomial number of required laser cuts (n nodes, n * (n-1) edges) and the source can be next to sink with a fake 0 edge between them.
- ljlolel 3y agoSeems doable. Or better do a problem that is NP-Complete or in a highly parallelizable class. Essentially an analog computer. Some of the reason people want quantum or DNA computers to exploit physical mechanisms beyond stacks of binary gates.
- pishpash 3y agoA (classical) analog computer is not a quantum computer and various conjectures on complexity say that they should all be efficiently (polynomial-time) simulated by a probabilistic Turing machine.
- teraflop 3y agoNo, it would give you the approximate shortest (least resistance) path between the source and sink, which is very different from the traveling salesman problem (which requires finding the shortest path that touches every node). I say "approximate" because, as has been discussed in this thread, the current actually follows every possible path to some extent, weighted by their resistance. So when there multiple branching paths with similar costs, they will have similar current flow, and the current along each path is not constant. So in general it can be difficult to find the exact minimum resistance path just by measuring the current.
- px43 3y agoOr.. use non-conductive coated wire to wire up every possible path, with all the wires connected at a start and finish point, and then see which wire gets hot first. It's not going to save you any time, since wiring up every path is basically the same as brute forcing every path anyway, but it would work.
- 3y ago
- strstr 3y agoNothing in this video is super groundbreaking if you’ve taken a typical physics class that includes some E&M. That said, the demonstrations are pretty compelling and well executed. I particularly liked the use of an IR camera to visualize the resistive power loss in the maze. Super cool.
- irrational 3y agoWell, I never took a physics course, with or without E&M (whatever that means), so I appreciated it.
- consilient 3y ago> E&M (whatever that means) electricity and magnetism
- throwaway8503 3y ago'electricite du magnetisme' would be a nice quadruple-entendre in French 1) electricity of magnetism => electrical side of the electromagnetic force leads to 2) electricity from magnetism => generating electricity from a magnetic force leads to 3) edm => electronic dance music leads to 4) excitement from attraction => the feeling of excitement ('electric' metaphor for excitement) from meeting someone you're attracted to ('magnetic' metaphor for attraction between two people)
- photochemsyn 3y agoGravity is the driving force behing the flow of water in this example, and a static electromagnetic field (in a DC circuit at least) is the driving force behind the flow of electrons. The water can do work on physical object (waterwheels, etc), and the electrons can do work on electrical loads (lightbulbs, etc.). However the static electromagnetic field in the DC circuit propagates through the material at near light-speed once the battery switch is thrown, which is a bit different. I suppose if you could throw a switch and turn gravity on or off it would be a closer analogy, i.e. the idea would be to fill the (sealed) maze with water in a zero-g environment (it would fill everywhere equally, comparable to the electons in the conductor with the power off), then turn on the gravity (or the pressure differential for the pipe version) and see what happened.
- derefr 3y ago> suppose if you could throw a switch and turn gravity on or off it would be a closer analogy I mean, you could, insofar as you can mechanically control the height difference between the start and end of the maze. I think the real problem with the analogy was just that the hydrodynamic version wasn't a circuit in the sense that the electrical version was. The water just falls out of the system, so of course you can't control the pressure difference :) The exit of the hydrodynamic version should have been a (sealed) pipe that flows into an (open) buffer-chamber thatis after the maze; from which a pump operating on a control system then brings pumps water back to the (open) buffer-chamber that sits before the maze. Additionally, said pump's speed should be determined by the water-level imbalance between the two buffer-chambers, such that it's always trying to bring the two chambers into water-pressure equilibrium. (This pump is then a proper hydrodynamic analogue of a generator: two terminals with a constant height [voltage] differential between them, that pumps faster or slower [= varies current] to maintain the same potential difference in the system, whether the system is loaded or unloaded.) Then "turning off gravity" would just mean moving everything (the input buffer, maze, output buffer, and pump) from being in a vertically descending sequence (where the pump would be doing constant work to maintain the potential difference despite the "load"), to being on a flat plane (where everything would reach potential equilibrium, and the pump would then turn off.) And you could then represent AC flow, by just alternatingly raising and lowering the two chambers, and using a bidirectional pump.
- shagie 3y agoThis reminds me of the Shannon switching game ( https://en.wikipedia.org/wiki/Shannon_switching_game https://en.wikipedia.org/wiki/Shannon_switching_game ) > Two players take turns coloring the edges of an arbitrary graph. One player has the goal of connecting two distinguished vertices by a path of edges of their color. The other player aims to prevent this by using their color instead (or, equivalently, by erasing edges). The game is commonly played on a rectangular grid; this special case of the game was independently invented by American mathematician David Gale in the late 1950s and is known as Gale or Bridg-It. That game, if modeled as an electrical circuit of resistors has the property that the best play is the one with the most voltage across it. https://boardgamegeek.com/boardgame/123102/bird-cage https://boardgamegeek.com/boardgame/123102/bird-cage > The game's original incarnation was as a machine built by the game's designer, noted engineer Claude Shannon. The machine would choose its' move by measuring electrical resistance between its' sides of the square and would reportedly win "almost always" when making the first move.
- segfaultbuserr 3y agoI vaguely remember reading about an impedance matching game, but I can't find it anymore. The goal of the game was moving the projectile to the correct location, and that projectile follows the same kind of curve produced by a reactive load on the Smith chart.
- kuon 3y agoWhat is "cool", (or a challenge if you design PCB like I do), is that this is not true for alternating current. For example, if you have a track that does a L on top side, and copper plane on bottom side, with an alternating signal, the return path will follow the L and not go back in a straight line. Those links have some explanations: https://resources.altium.com/p/what-return-current-path-pcb https://resources.altium.com/p/what-return-current-path-pcb https://www.nwengineeringllc.com/article/how-to-design-your-pcb-return-current-path.php https://www.nwengineeringllc.com/article/how-to-design-your-... https://electronics.stackexchange.com/questions/360472/real-current-return-path https://electronics.stackexchange.com/questions/360472/real-...
- codetiger 3y agoMy understanding about electronics basics is taking a hit, after reading this piece of info.
- __MatrixMan__ 3y ago> With time-varying signals, the return current follows the path of least reactance, which is also the path of least impedance. This means the return current path in your PCB is determined entirely by the impedance of the circuit that carries the return current. I was also a bit surprised by this. But I do recall doing equations regarding capacitive and inductive reactance. In both cases there is a frequency-dependent effect which alters the shape of the waveform. It being frequency dependent, it disappears in the presence of DC (inductors becoming irrelevant and capacitors becoming nonconductive). So I can kind of see it. But not enough to turn it into a return-path-is-suprising type example.
- nine_k 3y agoThere's electric field created by the L-shaped conductor a millimeter away. No wonder that it affects electrons in the larger conductor. School physics teaches us that metals are perfect conductors of electric field, so the field in the large conductor should be the same across it, and not follow the L shape. But it's only true for a stationary situation, basically DC. At higher frequencies the fact that the conductor (every part if it!) has some capacitance and inductance starts to play a major role in how a fast-changing signal propagates over it. Both the capacitance and the inductance of the part of the large conductor under the L-shaped conductor on the other side are affected by the L-shaped conductor. These considerations could help see the result as "more intuitive".
- steve76 3y ago[dead]
- low_tech_punk 3y agoGreat use of analog computer! Makes me think this Veritasium espisode: https://www.youtube.com/watch?v=GVsUOuSjvcg https://www.youtube.com/watch?v=GVsUOuSjvcg
- lucas_membrane 3y agoNot all the electrons follow the path of least resistance. The currents in parallel paths are in inverse proportion to the resistances of the respective branches.
- dcow 3y agoYeah. I mean neat video but the title baited me a bit. I thought maybe there was some unintuitive insight or interesting physical phenomenon happening that allowed electrons to solve a computationally hard problem better than the naive brute force, but it’s just 100 level physics.
- mrguyorama 3y agoHe notes this in the video and demonstrates it with two more mazes that have multiple solutions.
- jbverschoor 3y agoThe final experiment at the end was cool. It really is exactly like water
- Etrnl_President 3y agoThis also applies to economics.