It is the branch of science which deals with the electron flow through a vacuum , gas or semiconductor .
Classification of substances on the basis of conduction of electricity .
Solid
We know that , each substance is composed of atoms . Substances are mainly classified into three categories namely solids , liquids and gases .
In each solid atoms are at a definite positions and the average distance between them is constant .
Depending upon the internal arrangement of atoms , solids are further divided into two groups .
1 . Crystalline Solids
The solid in which the atoms are arranged in a regular order are called the crystalline solids . In other words , we can say that in a crystalline solid . there is periodicity and regularity of its component atoms in all the directions . For example sodium chloride ( common salt ), diamond , Sugar , silver etc are the crystalline solids .
Their atoms are arranged in a definite geometrical shape . They have a definite melting point .
They are anisotropic , i . e ., their physical properties such as thermal Conductivity refractive index etc , are different in different directions .
They are the real solids .
2 . Amorphous Solids
The Solids in which the atoms do not have a definite arrangement are called the amorphous solids . They are also called the glassy solids . For example glass , rubber , plastic , power , etc are the amorphous solids .
Tbey do not have a definite arrangement of its atoms , i e ., they do not have a characteristic geometrical shape .
They do not have a definite melting point .
They are isotropic . i . e ., their physical properties such as conductivity of heat refractive index etc , are same in all the directions .
They are not the real solids .