Conductors and Insulators
Idealized point charges and constant electric fields may
be exciting, but, you may ask, what about the real world? Well,
in some materials, such as copper, platinum, and most other metals,
the electrons are only loosely bound to the nucleus and are quite
free to flow, while in others, such as wood and rubber, the electrons
are quite tightly bound to the nucleus and cannot flow. We call
the first sort of materials conductors and the second insulators.
The behavior of materials in between these extremes, called semiconductors,
is more complicated. Such materials, like silicon and germanium,
are the basis of all computer chips.
In a conductor, vast numbers of electrons can flow freely.
If a number of electrons are transmitted to a conductor, they will
quickly distribute themselves across the conductor so that the forces
between them cancel each other out. As a result, the electric field
within a conductor will be zero. For instance, in the case of a
metal sphere, electrons will distribute themselves evenly so that
there is a charge on the surface of the sphere, not within the sphere.