what is corona discharge ? how is this principle related to van de graaf generator?
Van de Graaff generator works on the principle of corona discharge, based on 'action at points'. The tip of a pin is highly curved (i.e. radius of curvature is small). If it is charged,
intense electric field arises near the pointed end. A few free electrons are there in air, produced by the ionising radiations. These free electrons are accelerated by the intense electric field at the pointed end. Suppose the charge on the pointed end is positive. Then these positive charges will attract an equal negative charge from air and neutralize the charge on the tip of the pin. At the same time, positive ions are strongly repelled from it, to create the electric wind. This process, by which the charge at the pointed end of a conductor gets discharged is called corona discharge.