The Speed Of An Electric Current
Electrical currents move through wires at a speed only slightly less than the speed of light. The electrons, however, move from atom to atom more slowly. Their motion is more aptly described as a drift. Extra electrons added at one end of a wire will cause extra electrons to appear at the other end of the wire almost instantly. Individual electrons will not have moved along the length of the wire but the electric field that pushes the charge against charge along the conductor will be felt at the distant end almost immediately. To visualize this, imagine a cardboard mailing tube filled with ping-pong balls. When you insert an extra ball in one end of the tube, an identical ball will emerge from the distant end almost immediately. The original ball will not have traveled the length of the tube, but since all the balls are identical it will seem as if this has happened. This mechanical analogy suggests the way that charge seems to travel through a wire very quickly.
Science EncyclopediaScience & Philosophy: Dysprosium to Electrophoresis - Electrophoretic TheoryElectric Current - The Speed Of An Electric Current, Electric Current And Energy, Electric Current And Magnetism, Alternating Current - Current and the transfer of electric charge, Direct current