Conductors. Those substances which allow electric current to pass through them are called conductors e.g. metals, aqueous solution of salts, ionized gases, human body etc. In conductors, there are free electrons which account for their ability to conduct current through them.
Insulators. Those substances which do not allow electric current to pass through them are called insulators e.g. glass, mica, pure water, all gases etc. In insulators, the electrons are strongly bound to their atoms.
Dielectrics. Insulators are also called dielectrics. They do not conduct electricity but on applying electric field, induced charges are produced on their faces. Thus dielectrics may be defined as the insulating materials which transmit electric effect without conducting.
Behaviour of a conductor inside the electric field
When a conductor is placed inside an electric field, the free electrons in the conductor start drifting under the influence of electric field. The free electrons move towards the positive side. As the electrons leave the atom, it makes the atom +vely charged. The atom cannot change its position in the solid, but due to the drift of electrons the positive charges on the atom goes on shifting towards the -ve side. Finally +ve and -ve charges appear on the surface of the conductor which are equal in magnitude and are called induced charges. These induced charges produce their own electric field inside the conductor. The drift of electrons stops, when the internal electric field due to induced charges become equal to external field. Hence net electric field inside the conductor is zero.
