Theorie van metaalgeleiding

When an electric field is applied across a conductor, free electrons drift in the direction opposite to the field's direction while colliding with the crystal's ions.

If the applied field were zero, the random motion would, on average, result in zero net drift as the collisions would randomly change their directions. The average time between collisions is called the mean free time.

The electron's acceleration is given by the electric force over the mass. Its velocity at any time is expressed by the initial velocity, the acceleration, and the time.

Averaging both sides over the collisions gives the average velocity. However, since the average drift due to collisions is zero, the drift velocity is given by the product of acceleration and the mean free time.

Using the relationship between the current density and the drift velocity, the current density is related to the electric field, which is Ohm's law.

So, the electrical conductivity is expressed by the number of free electrons per unit volume, the electron's charge and mass, and the mean free time.