Re electron velocity in copper wire:
Although the drift velocity in a wire is small, the thermal velocity of the electrons tends to be quite large. Something of the order of 100,000 meters/sec. So they are buzzing about at random at high speeds, with a small superimposed drift velocity caused by the electric field.
Electric current is essentially a measure of how many charge carriers you can move through a given cross-section of conductor in a given amount of time. This will depend on the size of the cross section, the number of charge carriers, and their velocity. A current of 1 A corresponds to a transfer of 1 Coulomb of charge per second. An electron carries 1.6*10-19C so you need to move 6.3*10^18 electrons/sec. Divide by the density of electrons in a copper wire (about 8.45*10^22 electrons/cm^3) and the cross section of the wire (for AWG 18 this is pi*(1.02mm/2)^2 or 0.008 cm^2) and you get 0.0093 cm/s.
Summary - the net velocity of electrons in copper wire is extremely small. Recall the electrons are not (rpt not) the signal. They are the charge carrier. The signal is an electromagnetic wave the velocity of which is near lightspeed. The electromagnetic wave moves near lightspeed because the wave is comprised of photons, not electrons.
- Your friend and humble scribe
Although the drift velocity in a wire is small, the thermal velocity of the electrons tends to be quite large. Something of the order of 100,000 meters/sec. So they are buzzing about at random at high speeds, with a small superimposed drift velocity caused by the electric field.
Electric current is essentially a measure of how many charge carriers you can move through a given cross-section of conductor in a given amount of time. This will depend on the size of the cross section, the number of charge carriers, and their velocity. A current of 1 A corresponds to a transfer of 1 Coulomb of charge per second. An electron carries 1.6*10-19C so you need to move 6.3*10^18 electrons/sec. Divide by the density of electrons in a copper wire (about 8.45*10^22 electrons/cm^3) and the cross section of the wire (for AWG 18 this is pi*(1.02mm/2)^2 or 0.008 cm^2) and you get 0.0093 cm/s.
Summary - the net velocity of electrons in copper wire is extremely small. Recall the electrons are not (rpt not) the signal. They are the charge carrier. The signal is an electromagnetic wave the velocity of which is near lightspeed. The electromagnetic wave moves near lightspeed because the wave is comprised of photons, not electrons.
- Your friend and humble scribe