Those substances which allow electricity 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 conductors.
Those substances which do not allow electricity to pass through them easily are called insulators.
Most of the non-metals like glass, porcelain, plastic, nylon, wood offer high resistance to the passage of electricity through them.
Insulators are also called Dielectric. Obviously, dielectric cannot conduct electricity. However, when a electric field is applied, induced charges appear on the surface of the dielectric. Hence we may define dielectric as the insulating material which transmits electric effects without conducting.
When we bring a charged body in contact with the earth, all the excess charge on the body disappears by causing a momentary current to pass to the ground through the connecting conductor (such as our body). This process of sharing the charges with the earth is called grounding or earthing.
Some of these questions which may be asked in your Board Examination 2012-2013
Q1: Give some examples of Insulators?
Q2: Give some examples of Conductor?
Q3: Give some examples of Dielectric?
Q4: What else insulator may be called?
Q5: What are the types of substance found in nature?
Q6: How can we convert an insulator into a dielectric?
Answer these questions in comment box and help your friends