Page 31 - Basic Electrical Engineering

conductor as carrier of electricity is to allow electric current to flow with the
minimum of resistances, i.e., the minimum of opposition.
In a material where the outermost orbit of the atoms is completely filled,

the material is called an insulator. Insulators like glass, rubber, mica, plastic,
paper, air, etc. do not conduct electricity very easily. In the atoms of these

materials, the electrons tend to stay in their own orbits. However, insulators
can store electricity and can prevent flow of current through them. Insulating

materials are used as dielectric in capacitors to store electric charge, i.e.,
electricity.

Carbon, silicon, and germanium having atomic numbers of 6, 14, and 32,
respectively, are called semi conducting material. The number of electrons in
the outermost orbit of their atoms is four instead of the maximum of eight.

Thus, in the outermost orbit of a semiconductor material, there are four
vacant positions for electrons. These vacant positions are called holes. In a

material, the atoms are so close together that the electrons in the outermost
orbit or shell behave as if they were orbiting in the outermost shells of two

adjacent atoms producing a binding force between the atoms. In a
semiconductor material the atoms forming a bonding, called covalent

bonding, share their electrons in the outermost orbit, and thereby attain a
stable state. The condition is like an insulator having all the eight positions in
the outermost orbit filled by eight electrons. However, in semiconducting

materials, with increase in temperature it is possible for some of the electrons
to gain sufficient energy to break the covalent bonds and become free

electrons, and cause the flow of current.

1.4 ELECTRIC FIELD AND MAGNETIC FIELD
When charges are separated, a space is created where forces are exerted on

the charges. An electric field is such a space. Depending upon the polarity of
the charges, the force is either attractive or repulsive. Therefore, we can say

that static charges generate an electric field. An electric field influences the
space surrounding it. Electric field strength is determined in terms of the

force exerted on charges. A capacitor is a reservoir of charge. The two
parallel plates of a capacitor, when connected to a voltage source, establishes