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Most sources claim that the speed of electricity in a wire (or signal/information speed) is the EM wave propagation speed of the metal.

What about tangled wires? Am I correct in assuming that for the signal to pass a sharp turn in a wire, electrons need to accumulate there to make the "signal pass"? As electrons travel very slowly compared to the EM wave propagation, surely this adds a lot of delay to the signal?

Edit: made some pictures. In the initial moment, when connecting the wire, there's electric field at point 1, but none at points 2 and 3. When electrons accumulate on the first turn, there will be electric field in point 2 and so on. Is this understanding correct? Or is it more to do with EM waves somehow reflecting through the wire and no electron accumulation?

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    $\begingroup$ I am not sure what "sources" you have been using - the velocity of an EM wave in a wire is a function of the dielectric constant of the medium surrounding the wire. From wikipedia "In electrical cables, the velocity factor mainly depends on the insulating material (see table below)." $\endgroup$
    – Floris
    Commented Jul 19, 2016 at 17:30
  • $\begingroup$ The "signal" on a cable is not carried by the electrons but by the fields surrounding the cable. If you want the cable to actually contain the signal, rather than act as an antenna, then the fields have to stay close to it, which requires that the current return path be close (otherwise there will be an extended electromagnetic field). This leads to either twisted pair or coaxial cable designs. Those you can coil up without significant changes in their properties (sharp bends are excluded), but a single wire would only act like an antenna in your scenario. $\endgroup$
    – CuriousOne
    Commented Jul 19, 2016 at 19:10
  • $\begingroup$ Deleted the incorrect statement and made two figures $\endgroup$
    – eimrek
    Commented Jul 19, 2016 at 20:25

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You are confusing the drift velocity of the electrons (which is < 1 mm/sec) with their Fermi velocity (which is $1.57\cdot 10^6 ~\rm{m/s}$ for copper) - source. If any "bunching up" of electrons were to happen, it would very quickly resolve itself.

As was pointed out in the comments, the "signal" that travels in an electrical wire is essentially carried in the EM field (wave) surrounding the wire - and this propagates at the "speed of light" (in the medium surrounding the wire). Any change in electron distribution will immediately change the forces on nearby charge carriers. There is absolutely no effect of "electron inertia" in conventional conductors.

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  • $\begingroup$ Okay, so if the electric field propagated behind the turns by "bunching" of electrons, the speed order would be Fermi speed. (which is still ~100 times less than the speed of light and would slow down the signal, right?) But you're also saying that the signal does not travel behind the turn by bunching, but by somehow the EM wave reflects from the conductor-insulator surface. Can you elaborate, how exactly does the EM wave get around the turn? $\endgroup$
    – eimrek
    Commented Jul 20, 2016 at 10:30

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