. E LECTROSTATICS OF C ONDUCTORS Conductors and insulators were described briefly in Chapter . Conductors contain mobile charge carriers. In metallic conductors, these charge carriers are electrons.
In a metal, the outer (valence) electrons part away from their atoms and are free to move. These electrons are free within the metal but not free to leave the metal. The free electrons form a kind of ‘gas’; they collide with each other and with the ions, and move randomly in different directions. In an external electric field, they drift against the direction of the field.
The positive ions made up of the nuclei and the bound electrons remain held in their fixed positions. In electrolytic conductors, the charge carriers are both positive and negative ions; but the situation in this case is more involved – the movement of the charge carriers is affected both by the external electric field as also by the so-called chemical forces (see Chapter ). We shall restrict our discussion to metallic solid conductors. Let us note important results regarding electrostatics of conductors.
. Inside a conductor, electrostatic field is zero Consider a conductor, neutral or charged. There may also be an external electrostatic field. In the static situation, when there is no current inside or on the surface of the conductor, the electric field is zero everywhere inside the conductor.
This fact can be taken as the defining property of a conductor. A conductor has free electrons. As long as electric field is not zero, the free charge carriers would experience force and drift. In the static situation, the free charges have so distributed themselves that the electric field is zero everywhere inside.
Electrostatic field is zero inside a conductor . . At the surface of a charged conductor, electrostatic field must be normal to the surface at every point If E were not normal to the surface, it would have some non-zero component along the surface. Free charges on the surface of the conductor would then experience force and move.
In the static situation, therefore, E should have no tangential component. Thus electrostatic