Question

plz explain van de graaf's generator in detail

Answer 1

Van de Graaf is an electrostatic device which is used to produce large electrostatic potential difference of the order of 10 power 7 volts.
it is based on action of points and electrostatic induction.
It was devised by Robert j van de Graaf 
it consists of hollow metal sphere mounted on an insulating pillar.
a pulley say B is in the center of the sphere.
another pulley say C is in the bottom of the sphere.
a belt made of silk runs over the two pulleys.
Pulley c is driven by an electric motor
Two comb shaped conductors d and e with many needles are mounted near c and b
d is maintained at 10 power 4 volt by a power supply.
e is connected to the inner surface of the sphere
because of the high voltage at d, air gets ionised
negative charges move towards the needles
positive charges are repelled on the belt. The charges stick to the belt and reach near E
at E due to electrostatic induction the needles acquire negative charge
the sphere acquires positive charge which gets distributed on its outer surface
the descending belt is uncharged
the potential of the sphere keeps increasing until it reaches a maximum value.