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NEOCLASSICAL THEORY OF INTERACTION 59

= + +

= + + � (2.29)

= + +

A good example of such medium is the ionosphere, the layer of the earth's atmosphere that
contains a varying from point to point high concentration of ions and free electrons and extends
from about 80 to 1000 km above the earth’s surface.
2.2.7 Polarized Conductive Body in Electric Fields
An interesting consequence of the formula (2.28) is that the free charges must leave a
homogeneous
conductive material
very fast under the
influence of external
E-field. Meanwhile,
we know that they
cannot vanish without
traces and thus must
be accumulated
somewhere. Suppose
a) b) that the piece of
conductive material as
Figure 2.2.9 Insulated perfectly conductive sphere situated in a metal sphere is
external uniform electric field : a) separation of charges, b) 3D located in a vacuum

distribution (numerical simulation) and thoroughly
insulated. Evidently,
E-field can move the free electrons inside the sphere to the body boundary only and hold them
there . As such, the infinitesimally thin (in term of macroscopic electrodynamics) layer of
9
charges is formed on the body boundary as shown in Figure 2.2.9 on the example of an insulated
perfectly conductive uncharged sphere situated in the external uniform electric field . We
assumed that the producing charges (not shown in picture) are so far away that they are
unaffected by the presence of sphere. Then these external negative charges (thick minus blue
sign) in compliance to Coulomb’s law exert through E-field repelling force on free electrons in
sphere moving them to the left and towards the external positive charges (thick plus red sign)
as shown in Figure 2.2.9. Since the shortage of electrons on the right surface of sphere means
excess of positive charges there, the external E-field maintains the charges separation on sphere
surface. Figure 2.2.9b illustrates the numerically simulated distribution of surface charges and
fields matching the schematic drawing in Figure 2.2.9a.
Looking back at Figure 2.2.9a and compare it with 2.1.6 we can come to the conclusion that a
small metal sphere creates the induced polarization field P (shown in green) which similar to
polarized molecular dipoles within a natural dielectric. If so, dispersing in periodic lattice-like
shown in Figure 2.2.10 multiple and insulated from each other metal microspheres in a little
weight dielectric matrix like foam we can develop the artificial dielectric materials with a broad
spectrum of relative dielectric constants different from one and even including negative

9 Note that very strong E-field might force electrons to leave the conductive body creating so-called field
electron emission. This effect will be considered in Section 3.3.3 of Chapter 3.