Van de graff generator is an electrostatic generator first designed in 1931. it is capable of producing potential difference of about 6 to 10 million volts. Such a high voltage is made use of to accelerate charged particles to carry out nuclear reactions.
Principle
If a charged coductor is brought into internal contact with a hollow counductor, all of its charge gets transferred to the hollow conductor, irrespective of its own potential
Construction
It consists of a spherical metal shell mounted on an insulating stand ( glass, plastic ) above the ground.
A long narrow belt of an insulating material like rubber (or silk ) is wound around two pulleys p1 and p2.
Pulley p1 is at the center of the spherical shell and p2 is at the ground level. The belt is made to rotate with the help of a motor.
Working
Positive charges are sprayed to the belt by a brush b2 near the bottom. This brush made of copper collects electrons from the rubber while it is rubbed. (copper being more electro negative than rubber), thus leaving out positive charges on the belt. b2 is earthed using a wire. The electrons thus collected in the brush b2, flows to ground.
The positive charges are carried up along the rubber belt. The collecting brush b1 on top transferes these charges
from the belt to the inner portion of the spherical shell. The charges are "Switched" to the outer sufrace of the shell instantily.
As the belt continues to rotate, more and more positive charges gets collected on the shell, which rises its potential to a high value.
Video by http://www.youtube.com/user/CarletonPhysics
Physics lab demo 3
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