The matter on the earth which occupies the
space may be solid, liquid or gaseous. The matter is made up of one or more
elements. Each element is made up of many atoms which are of similar nature.
Now a days, scientists are successful in breaking atoms and studying the
resulting products.
According to
modern electron theory, atom is composed of the three fundamental particles,
which are invisible to bare eyes. These are the neutron, the proton and the
electron. The proton is positively charged while the electron is negatively
charged. Te neutron is electrically neutral i.e. possessing no charge. The mass
of neutron and proton is same which is 1.675 x 10-27 kg while the mass of electron is
9.107 x 10-31 kg. the magnitude of positive charge on proton is same as the magnitude
of negative charge on electron. Under normal conditions, number of protons is
equal to number of electrons hence, the atom as a whole is electrically
neutral. All the protons and neutrons are bound together into a compact
nucleus. Nucleus may be thought as a central sun, about which, the electron
revolve in a particular fashion. The electrons are arranged in different orbits
i.e. levels. The orbits are also called shells.
The orbits are
more or less elliptical. The electrons revolving in various orbits are held by
force of attraction exerted by nucleus. The orbit which is closest to the
nucleus is under tremendous force of attraction while orbit which is farthest
is under very weak force of attraction. Hence, electrons revolving in farthest
orbit are loosely held to the nucleus. Such a shell is called valence shell and
the electrons in this shell are valence electrons. In some atoms, at room
temperature only, these valence electrons gain an additional energy and they
escape from the shell. Such electrons exist in an atom as free electrons. Now,
if such electrons are removed from an atom, it will loose negative charge and
will become positively charged. Such positively charged atom is called anion.
As against this, if excess electrons are added to an atom, it will become
negatively charged. Such negatively charged atom is called cation.
Note : This
total deficiency or addition of excess electrons in an atom is called as its
charge and the atom is said to be charged. The unit of charge is coulomb.
The deficiency
or excess of electrons can be achieved by different methods. One of such methods
is to rub two dissimilar materials against each other. When an ebonite rod is
rubbed on a fur cloth, then the rod extract electrons from fur cloth and
behaves as negatively charged while fur cloth behaves as positively charged.
This charged condition of rod cannot be sensed by eyes or by any sense organs.
But, we can observe the effect of it by simple experiment. Such charged ebonite
rod, when brought near light pieces. This attraction is nothing but the effect
of static charge present on the rod. This the basic principle of the static
electricity.
Such
phenomena due to static charge are governed by some laws called of electrostatics.