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how does electricity propagate in a conductor?

I have read that in an electrical wire electrons movement is very slow while the energy or charge is very fast. What's the difference anyway?


marked as duplicate by Qmechanic, Manishearth, Emilio Pisanty Dec 11 '12 at 10:36

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    $\begingroup$ I think there's a mistake in your title. Should it be "What's the difference between electron movement and signal movement in electricity?" I ask because "electron movement" and "charge movement" is the same thing in an electrical circuit. $\endgroup$ – John Rennie Sep 25 '12 at 16:03
  • $\begingroup$ @JohnRennie, that's not quite true. Charge movement (electric current) is an abstract current. Electron movement (electron current) is a physical current. Though an electron current is necessarily an electric current, an electric current is not necessarily an electron current. $\endgroup$ – Alfred Centauri Sep 26 '12 at 1:40
  • $\begingroup$ It seems the question(v1) is essentially covered in physics.stackexchange.com/q/17741/2451 and physics.stackexchange.com/q/335/2451 $\endgroup$ – Qmechanic Oct 25 '12 at 19:23

I'm sure this is a duplicate question, but I've searched and haven't found an exact duplicate.

Anyhow, an analogy commonly used is to imagine the electricity flowing in a circuit as water flowing in a water pipe. In this analogy the electrons are the water and the voltage is the water pressure. The battery in the circuit would be represented as a pump.

If you suddenly increase the pressure of the water e.g. by turning the pump on (equivalent to connecting the battery) then the pressure change will flow round the circuit fast. In fact it would move at the speed of sound in water, which is about 1.5 km/sec, even though the water would be moving much more slowly than this.

Going back to the electric circuit, the signals travelling round the circuit are changes in voltage and move at around the speed of light just as the pressure does in a water circuit. However the electrons would be moving far slower than this.

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    $\begingroup$ It was a favorite qualifying exam question at Rutgers. I think that the electrons' drift velocity is just something like 10 centimeters per second, far lower than the near-speed of light for the signal. $\endgroup$ – Luboš Motl Sep 25 '12 at 16:42
  • $\begingroup$ I got asked this question in my interview for a place as an undergraduate at Cambridge. I got the place :-) $\endgroup$ – John Rennie Sep 25 '12 at 17:02
  • $\begingroup$ Good for you! ;-) $\endgroup$ – Luboš Motl Sep 25 '12 at 17:22
  • $\begingroup$ That was 32 years ago, before I give everyone the impression I'm a virile young undergraduate. Yes, they had electricity when I was an undergraduate :-) $\endgroup$ – John Rennie Sep 25 '12 at 17:32
  • $\begingroup$ @JohnRennie Cambridge was top dog then ;) Which college? $\endgroup$ – Physiks lover Sep 25 '12 at 18:19

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