4 ms·
> you can have an electromagnetic wave traversing the wire at some proportion of the speed of light, while the electrons are moving at speeds closer to meters p
by jstanley 3y ago
> you can have an electromagnetic wave traversing the wire at some proportion of the speed of light, while the electrons are moving at speeds closer to meters per second.
This isn't as unintuitive as it sounds though.
In a water pipe you can have a pressure wave reach from one end to the other very quickly, even as the individual water molecules move very slowly.
If water pressure is voltage, water molecules are electrons, and the pipe is the wire, then it's easy to see how a "voltage" can reach the other end of a "wire" without any of the "electrons" having to move very far at all.
- jocaal 3y agoThe problem with this analogy is that pressure waves can only travel in a medium. The pressure wave exists because the particles in the medium bump against eachother to propagate energy so the analogy gives people the impression that electrons are bumping against eachother to propagate energy. Photons are distinct entities that can travel without a medium. See michelson-morley experiment. Electricity is nothing like what we experience on our macro scale. Analogies never convey the full story.
- jstanley 3y ago> the analogy gives people the impression that electrons are bumping against eachother to propogate energy. If this is not approximately how electricity works, why does the current stop flowing when you disconnect the wires, or equivalently when you "connect" them via something that doesn't have free electrons (i.e. an insulator)?
- jocaal 3y agoUnfortunately the explanation to your question is something that takes years of education to understand and even then, most people just come out understanding some parts. The best I can do on an internet forum is tell you that the analogy is wrong, because experiments told us its wrong. My advice is if you want to understand this stuff, do the math! ;)
- jstanley 3y agoThe water analogy makes perfectly good predictions for the kinds of things I do with electricity, so in that respect I find it useful. As any analogy, it is not the same as the thing it is an analogy of, but an analogy can be useful without being complete.
- ben_w 3y agoThere was a whole mess of STEM YouTubers arguing about this last year, e.g.: https://youtu.be/oI_X2cMHNe0?si=-PzCPZ5qNiS9nYFW https://youtu.be/oI_X2cMHNe0?si=-PzCPZ5qNiS9nYFW TL;DW: the power is transferred by the electric fields, it's the electric fields which move the electrons, if there's a break in the circuit the electrons necessarily accumulate in the places that minimise the electric fields.
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- roelschroeven 3y agoThe analogy does not completely explain the actual behavior of electrical current, that's true. But what's more important, and what it does clearly show, is that a fast wave can exist without fast movement of the particles involved.
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