TABLE OF CONTENTS In this chapter, we shall use Maxwell's equations to investigate the interaction of dielectric and magnetic media with quasi-static electric and magnetic fields.
The terrestrial environment is characterized by dielectric media ( e.g., air, water) which are, for the most part, electrically neutral, since they are made up of neutral atoms and molecules. However, if these atoms and molecules are placed in an external electric field then they tend to polarize: i.e., their positively and negatively charged components displace with respect to one another. Suppose that if a given neutral molecule is placed in an external electric field E then the center of charge of its constituent electrons, whose total charge is (say) q, displaces by d with respect to the center of charge of its constituent atomic nuclii. The dipole moment of the molecule is defined as p = q d. If a dielectric medium is made up of N such molecules per unit volume then the electric polarization, P, of the medium (i.e., the dipole moment per unit volume) is given by P = N p. More generally,
where ? p i ? is the average dipole moment of the ith type of molecule making up the medium, and N i the average number of such molecules per unit volume, in the vicinity of point r.
Now, we saw previously, in Exercise 3.4, that the scalar electric potential field generated by an...
