Materials which allow flow of current through them are called conductors. They contain free electrons which are donated by the atoms to the material as a whole and are able to move around freely inside the material.
These electrons come from the outermost orbit of atoms as they are very loosely bound to the atom.
The electrostatic behaviour of an insulated charged conductor or a conductor placed in an electric field can be summarized as follows.
(a) The electric field in the interior of the conductor is zero everywhere.
(b) The electric field immediately outside the surface of the conductor is perpendicular to the surface.
(c) Any excess charge given to a conductor remains on the outer surface.
(d) All points on and within the surface of the conductor are at the same potential.
It follows that there is no difference between the electrostatic behaviour of a solid conductor and a hollow conductor of the same shape and size.
ELECTROSTATIC SHIELDING
If there is a cavity of any shape inside a conductor, the field there will be strictly zero. This property is called electrostatic shielding because any thing placed inside the cavity will be completely shielded from external fields.
Examples : In a thunderstorm accompanied by lightning, it is safer to be inside a car, rather than near a tree
or on the open ground.
CONDUCTOR HAVING SHARP POINTS (ACTION OF POINTS)
Another interesting result is that the charge density and the electric field tend to be relatively high on sharp points and low on plane regions of a conducting surface. This can be attributed to the fact that charge density is proportional to radius of curvature.
Glow discharges from sharp points during thunderstorms are due to this reason. The lightning rod, which has sharp points, is thus able to neutralize charged clouds and prevent lightning strokes.
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