1.3 Conductors and Insulators

    A metal rod held in hand and rubbed with wool will not show any sign of being charged. However, if a metal rod held with a wooden or plastic handle is rubbed, it shows signs of charging. Why? Some substances readily allow passage of electrons throught them, others do not. Those which allow electrons to pass through them easily are called conductors. They have electric charges( Electrons) that are comparatively free to move inside the material. Metals, human and animal bodies and earth are conduction. Most of the non-metals like glass,porcelain, plastic,nylon,wood etc. Offer high resistance to the passage of electricity through them. They are called insulators. Most substances fall into one the two classes stated above.
              When charge is transferred to a conductor, it readily gets distributed over the entire surface of the conductor. In contrast, if some charge is put on an insulator, it stays at the sample place. When we bring a negatively charged body in contact with the earth, all the excess charge on the body disappears by a momentary flow of electrons to the group through the connecting conductor( such as our body).  If a positively charged body is connected to the earth, electrons flow from the earth to the body. This process of sharing the charges with the earth is called grounding or earthing. Everything provides a safety measure for electrical circuits and appliances.