Conductors and Insulators:
Conductor: The material which allows the electric current to pass through it is known as a conductor. The best conductor is which offers least resistance to the flow of electric current through it. The conductors have a number of free electrons which get excited on being heated or when the electric current passes through it.
Silver is the best conductor of electricity. Copper and aluminum are also considered good conductors of electricity so they are used to make electric wires.
The resistance of conductors’ increases as the temperature rises so the conductors offer more resistance to electric current at higher temperature.
Insulator: The material which offers resistance to the flow of electric current through it is known as an insulator. In insulators the electron are closely bound to the nucleus so there is no free electron available for excitation.
Examples of such insulators are graphite, glass and mica in which the electrons are very closely bounded to the nucleus.
Insulators lose their insulating power at high temperature.