Explain in detail the construction and working of a Van de Graaff generator.

Explanation

It is a machine which produces large electrostaic potential difference of the order of `10^(7)` V.
Principle:
Electrostatic induction and action of points.
Principle:
(i) It consists of a hollow metallic sphere A mounted on insulating pillars.
(ii) A pulley B is mounted at the centre of the sphere and another pulley C is mounted near the bottom.
(iii) A belt made of silk moves over the pulleys.
(iv) Two comb-shaped conductors D and E are mounted near the pulleys.
(v) The comb D is maintained at a positive potential of the order of `10^(4)` volt.
(vi) The upper comb E is connected to the inner side of the hollow metal sphere.

Working :
(i) Because of the high electric field near the comb D, the air gets ionized.
(ii) The negative charges in air move towards the needles and positive charges are repelled towards the belt due to action of points.
(iii) The +ve charges stick to the belt moves up end reaches near the comb E.
(iv) E acquires negative charge due to electrostatic induction.
(v) The acquired +ve charge is distributed on the outer surface of the sphere.
Thus the machine, continuously transfers the positive charge to the sphere.
(vii) The leakage of charges from the sphere can be reduced by enclosing it in a gas filled steel chamber at a very high pressure.
(viii) The high voltage can be used to accelerate positive ions for the purose of nuclear disintegration.