What is the speed of electricity, in the medium of small
copper wires? What is the speed of e-mail?
The speed of a charged particle in copper is very slow: about 0.01 cm/s.
At this rate, it takes about 3 hours for a charge to travel about one
meter. The electric field (signal) travels at the speed of light through
copper. The charge is not carrying the information, per se, but the
information is transmitted by the electric field. It is like a molecule of
water does not travel across the ocean, but the wave does.
Line up five hundred people. Call out, "Forward March!" They people move
at about 1 m/s, but the signal that gave them the marching order was the
speed of sound, or about 330 m/s. This is analogous to your question. The
charge moves very slowly, but the signal is very fast.
---Nathan A. Unterman
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Update: June 2012