Classification Of Materials In Terms Of Conductivity

CLASSIFICATION OF MATERIALS IN TERMS OF CONDUCTIVITY:

On the basis of the conductivity, the materials can be classified into the following categories.

(i) In certain materials, the outermost electrons of atoms/molecules are loosely bound. These electrons are almost free to move throughout the body of the material.

These are called free electrons. These free electrons participate in electrical conduction, therefore these are also called conduction electrons.  Due to their presence in large number, the materials have large value of conductivity. These materials are called conductors, e.g. copper, silver, etc.

(ii) Some materials have very low value of electrical conductivity. In these materials, the electrons are tightly bound to their respective atoms or molecules.  These materials are called insulators or dielectrics, e.g. glass, rubber, etc.

(iii) In one class of materials, the conductivity is greater than insulators but less than that of conductors.  These type of materials are called semiconductors. e.g. silicon, germanium etc.

Superconductivity

The resistivity of certain materials suddenly becomes zero below a certain temperature.  This phenomenon is called superconductivity and the material showing such behaviour is called superconductor.  Above the critical temperature TC (at which such transition occurs), the resistivity of the metal follows the trend of a normal metal as shown in graph A.

Graph (A)