Electromagnetism: Maxwell Equations, Wave Propagation and Emission

Chapter 3

Conductors and Currents

We have seen that materials may be classified as insulators or conductors, although the distinction is not clear cut, as semiconductors have a conductivity that is intermediary between conductors and insulators. Similar to heat conduction, some materials are better conductors than others. The historic Hall experiment has shown, even before the discovery of the electron, that conduction of metals is due to the motion of negative charges (see section 6.1). Actually, we know that the external electrons in some atoms are weakly bound; this makes them free to move from one atom to the other; these are the free electrons (or conduction electrons). In electrolytic solutions, the molecules are dissociated into two ions of opposite charge and both are free to move and contribute to electric conduction. In this chapter, we analyze the properties of solid conductors in equilibrium and study their conduction properties.

3.1. Conductors in equilibrium

In a body, each charge is subject to the electric field of the other bodies and that of the other charges of the body itself. If the body is a conductor, the free charges move very rapidly under the influence of these fields until they reach a stable electrostatic equilibrium configuration. Besides this orderly motion in a given direction, the particles have a random motion, called thermal agitation, which increases with temperature and which is equally probable in all directions if the temperature of the body ...