In a conductor like copper, the free electrons of the metal move very slowly under the effect of an electric field, as they are constantly slowed down by Brownian collisions with the ions of the crystal lattice and the impurities of the metal. Their average drift velocity is about 0.07 mm/s, comparable to that of a snail. Yet, when an electric field is applied to the end of the wire, the electromagnetic disturbance propagates almost at the speed of light, about 300,000 km/s.
Electricity does not consist of making electrons travel from one end of the wire to the other. When an electric field is applied, all the electrons in the conductor react at the speed of light, transmitting the disturbance instantaneously on a macroscopic scale.
One can imagine the electrons as reacting locally and almost instantaneously to the applied field, somewhat like a row of dominoes where the wave propagates very quickly, while each domino only moves a very short distance. In this way, the collective wave travels through the conductor almost at the speed of light from one end to the other, while the electrons themselves drift extremely slowly, at a speed comparable to that of a snail, traveling only a few millimeters per second.
| Phenomenon | Typical value | Comment |
|---|---|---|
| Drift velocity of electrons | ~ 0.07 mm/s | Extremely slow, due to frequent and disordered collisions in the crystal lattice |
| Propagation of the electric field | ~ 3 × 108 m/s | Almost instantaneous, like an electromagnetic wave that propagates rapidly through the wire, long before the electrons themselves move |
| Average thermal velocity of electrons | ~ 105 m/s | Brownian motion, does not contribute to the net current |
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