What is difference of conductors insulators and semiconductors.

CONDUCTORS, INSULATORS AND SEMICONDUCTORS.

Any piece of matter of moderate size contains millions and millions of atoms or molecules. Each atom contain a positively charged nucleus and several electrons going round it.

In gases, the atoms or molecules almost do not interact with each other. In solids and liquids, the interaction is comparatively stronger. It turns out that the material may be broadly divided into three categories according to their behaviour when they are placed in an electric field.

(a) Conductors 

In some materials, the outer electrons of each atom or molecule are only weakly bound to it. These electrons are almost free to move throughout the body of the material and are called free electrons. They are also known as conduction electrons. When such a material is placed in an electric field, the free electrons move in a direction opposite to the field . Such materials are called conductors.

(b) Insulators

Another class of materials is called insulators in which all the electrons are tightly bound to their respective atoms or molecules. Effectively, there are no free electrons. When such a material is placed in an electric field, the electrons may slightly shift opposite to the field but they can't leave their parent atoms or molecules and hence can't move through long distances. Such materials are also called dielectrics. 

(c) semiconductors

In semiconductors, the behaviour is like an insulator at the temperature 0 K. But at higher temperatures, a small number of electrons are able to free themselves and they respond to the applied electric field. As the number of free electrons in a semiconductor is much smaller than that in a conductor, its behaviour is in between a conductor and an insulator and hence, the name semiconductor. A freed electron in a semiconductors leaves a vacancy in its normal bound position. These vacancies also help in conduction.