On Fri, 31 Oct 2025 at 21:02, <[email protected]> wrote: > On Fri, 31 Oct 2025, [email protected] wrote:
> > The electrons move actually pretty slowly. It's the electrical field > > what moves quickly. > > Let's assume copper, at a density of 8.9 g/cm^3, and an atomic weight > > of 63.5: 1mm^3 of copper has 6.02*10^23 * 8.9 * 10^-3 * (1/63.5) atoms, > > i.e. 8.44 * 10^19 atoms, each contributing one electron to the > > conduction band (the last lone S1). At 1.6 * 10^-19 C, that makes 13.5C > > of charge available for conduction in each mm^3, which is a friggin' > > lot. > > If you push 1A across a wire with a cross section of 1mm^2, your > > electrons would be moving at 1/13.5 mm/s, i.e. 0.074 mm/s: I can hear > > the snails in my garden yawning :) > > I might have lost an order of magnitude here or there, but the kind > > of result is somewhat consistent with the dim memories I have from a > > former life... > i worked maintenance in a factory so i can't argue with any of that > but please clarify > is this 0.074 mm/s along the length of the conductor > what about moving in other directions > how far does an electron actually travel in one second Hi, there's more explanation here: https://en.wikipedia.org/wiki/Drift_velocity This example is for copper, different conductors have different electron mobilities, see: https://en.wikipedia.org/wiki/Electron_mobility "when an electric field is applied, each electron or hole is accelerated by the electric field. If the electron were in a vacuum, it would be accelerated to ever-increasing velocity (called ballistic transport). However, in a solid, the electron repeatedly scatters off crystal defects, phonons, impurities, etc., so that it loses some energy and changes direction. The final result is that the electron moves with a finite average velocity, called the drift velocity. This net electron motion is usually much slower than the normally occurring random motion." "the same conductivity could come from a small number of electrons with high mobility for each, or a large number of electrons with a small mobility for each" Metals are the latter, so the velocity is slow. In other other materials, for example semiconductors, the velocity is higher: https://en.wikipedia.org/wiki/Electron_mobility#Examples
