VAN DE GRAAF GENERATOR
Van De Graaff generator: It is an electrostatic generator capable of building a high potential difference in the order of 10⁷ volts.
Principal: The working of Van De Graaff generator is based on the following two electrostatic phenomena:
Discharging action of sharp points ( Corona discharge) that is electric discharge takes place in the air or gas readily at the pointed ends of the conductors.
If the charged conductor is brought into internal contact with a hollow conductor, all of the charge transfer to the hollow conductor, howsoever high the potential of the latter may be.
Construction: Large spherical conductor shell (of a few meters radius) is supported at a height several meters above the ground on the insulating column. A long narrow belt of insulating material, like rubber or Silk, is wound around to pulleys, p1 at ground level and P2 at the center of the cell.
This belt is kept continuously moving by an electric motor attached to the lower pulley P1. Near the bottom and the top of its run, the belt passes closer to two sharply pointed brass column B1 and the B2, pointing towards the belt. The comb B1, called spray comb is given a positive potential of 10-kilo volt with respect to the earth by means of a battery, while the comb B, is called collecting comb is connected to the spherical shell s.
Working: Due to the high electric field at the pointed end of the B1, the air of neighborhood gets ionized and its positive charge repelled or sprayed on the belt, which moves up into the shell S. As it passes close to the comb B2, induces a negatively charged at the pointed ends of B2 and a positive charge on the shell S. The positive charge spreads uniformly the outer surface of the shell S. The high Electric field at the pointed ends of the Comb B2 ionizes there air and repels the negative charge on the belt which neutralize its positive charge. The process continues as more and more positive charge in a given to the shell, its potential continues to rise. In this way, a high potential of six to eight million million volts can be built upon the sphere.
A discharge tube is placed with the upper and inside the hollow sphere and lower Earthed. The ion source is placed at the upper end of the tube. The high potential on the sphere repels the charged particle downward with the large acceleration, where the hit the target at on to bring about the nuclear disintegration.
Use: The high potential difference set up in the Van De Graaff generator is used to accelerate charged particles like the Proton, deuterons, Alpha particles, etc. To high energies of about 10 megavolts, needed for the experiment to prove the small scale structure of matter.
In class 12th board exam there can ask questions on this article for 1, 2, and 5 marks like ex.
Que no 1: Explain the basic principle of van de Graaff generator?
Que no 2: Give the construction and working of Van De Graaf Generator?
Que no 3 : What is Van De Graaf Generator ?