The effective speed at which electrons travel through a conductor, is much smaller

than often assumed. It is in the order of a millimeter per second. An electric current of

ten ampere for instance, represents an electron displacement of about 6 x 10^19

electrons per second at which the symbol ^ stands for "to the power of". 10^19 is a

short notation for a one with nineteen zeros or 10 billion billion. This seems to be a lot

of electrons but a copper wire with a cross-cut of one square millimeter and a length

of one meter contains about 10^23 copper atoms, as much as the number of tennis

balls that would fit into the moon. When we assume that one atom of copper

participating in the conduction, provides no more than one free electron, the effective

drift velocity of the electric charge through the wire would be about (6 x 10^19)/(

10^23) meter/second or 0,6 mm/second. What ìs fast however, is the propagation of

a current change. For copper this propagation speed is about 250.000 km/sec so a

change in current travels around the globe in about 160 milliseconds. This explains

why we can make a fixed wire phone call towards the other side of the earth with only

a small notable delay while it would take an individual electron about 1000 years to

reach the other side of the globe.