What is Van de Graaff generator?
It is a device which is used to built a potential difference of few millions of volts and this potential difference is required is to carry out the Nuclear Reactions i.e. the major application of this generator. It was invented in 1929 by American physicist Robert J. Van de Graaff. The potential differences achieved in modern Van de Graaff generators can reach 5 megavolts.
Working Principle of Van de graaff Generator:
It is based on the principle that the inner points of a conductor are always at high potential.so, when the charge is given to the inner points it immediately flow to the outer surface. thus the charge from high potential to low potential either by conduction or by induction.
Construction of van de graaff Generator:
These are the major construction parts for the making of this generator.
1) The Hollow metal sphere which are at the lower potential.
2) The Upper electrodes.
3) Upper metal roller with conveyor belt.
4) Side of belt having positive charge.
5) The Opposite side of conveyor belt having negative charge.
6) Lower metal roller.
7) Lower grounded electrode.
8) Spherical device having negative charge
9) Spark produced by the potential difference between two spheres.
Working of Van de Graaff generator:
From a high tension source the charge transfer to conveyor belt and the belt is moving charge reaches to the point 2 and the point 2 of the belt is connected to the outer metallic sphere.As the point 2 the high potential point. So,therefore the charge goes to the outer shell. This process is repeated many times till large amount of charge reaches to the outer surface of the shell.
AS V is directly proportional to Q so therefore a potential difference of few million of volts is developed at surface of the outer shell and same potential is developed at the inside points also. and the potential difference is given by
where r is the radius of the shell.