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How can AC provide energy if electrons don't have a net movement? In fact, an electric instrument requires electrons to work, for example in a light bulb the electrons go across it. But in AC circuits electrons don't go inside it, so how can it work?

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  • $\begingroup$ Do you realize how far an electron can travel in 1/60th of a second? $\endgroup$ – Hot Licks May 1 '18 at 0:18
  • $\begingroup$ @HotLicks Not very far inside a wire, due to a small mean free path. $\endgroup$ – probably_someone May 1 '18 at 0:22
  • $\begingroup$ Or see en.wikipedia.org/wiki/Drift_velocity for a typical numerical value... $\endgroup$ – DJohnM May 1 '18 at 0:24
  • $\begingroup$ What do you mean by net movement? A particle oscillating periodically back and forth clearly moves through a distance over one cycle even though the displacement is zero. $\endgroup$ – Alfred Centauri May 1 '18 at 1:13
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    $\begingroup$ How can you do work with a saw if the saw (and your arm) has no net movement? $\endgroup$ – Cort Ammon May 1 '18 at 1:18
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if @probably_someone's anology isn't clear, just consider an old-fashioned tree-felling saw with two handles. it cuts on both the instroke and the outstroke. in the same sense, AC power does work during both the going-positive and going-negative "strokes".

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The key is that there already are electrons inside the light bulb, so all you have to do is push on the electrons that are already there. Since electrons in a wire frequently collide with each other, you can imagine the electrons in the wire as behaving like water in a tank. In order to push the water in the middle back and forth, all you need to do is push and pull on the side of the tank.

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An electron inside the filament of a light bulb moves and gains kinetic energy from the local (oscillating) electric field and then collides with and gives energy to the ions in the lattice.

This transfer of energy happens whether of not the "mean" position of the electron changes during this process.

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