VAN DE GRAAFF GENERATOR, ITS PRINCIPLE,CONSTRUCTION AND WORKING.

V a N      d E     G r A a F f     G E n E r a T O r

A Van de Graaff  generator is a device designed to create static electricity and make it available for experimentation.
  
                      The American physicist Dr. Robert Jemison Van de Graaff invented the Van de Graaff generator in 1931. The device
has the ability produce extremely high voltages as high as 20 million volts. Van de Graaff invented the generator to supply the high energy needed  for early particle accelerators. these accelerators are known as atom smashers because they accelerate the sub-atomic particles to very high speeds and then "smashed" them into the target atoms. The resulting collisions created other subatomic particles and high energy radiation such as X-rays. The ability to create these high-energy collisions in the foundation of particle and nuclear physics.


PRINCIPLE:

The Van de Graaff generator works on the following two principles.

1. Discharging action of sharp points i.e., electric discharge takes place in air or gases readily at pointed conductors.
2. If the charged conductor is brought into internal contact with a hollow conductor , all of its charge transfers to the surface of the hollow conductor  no matter how high the potential of the latter may be.

CONSTRUCTION:

M- a large spherical conducting shell is supported at a height several meters from the ground on an insulator column.

B- an insulating belt wound around two pulleys P1 and P2, this belt is moving continuously by a driven motor at constant speed.

C1,C2- sharply pointed combs close to the belt near its bottom and top, C1 has given 10kV by a high-tension battery (HT) and termed as spray comb and C2 is connected to spherical shell and termed as collector comb.

WORKING:

The high electric field at the pointed end comb C1 ionises the air near them. The +ve charges in air are repelled and got deposited on the belt through a corona discharge. The charges are carried upto C2. A similar corona discharge takes place at C2 and the charges are finally transferred to the shell M. The charge spread over uniformly on the outer surface of M raising its potential to few million volts.