State the principle of a device that can build up high voltage of th
Answers
Device is Van - de graff generator.
Van de Graff generator is a device used for building up high potential differences of the order of a few million volts.
Such high potential differences are used to accelerate charged particlessuch as electrons, protons, ions, etc.
Principle It is based on the principle that charge given to a hollow conductor is transferred to outer surface and is distributed uniformly over it.
Construction:
It consists of a large spherical conducting shell (S) supported over the insulating pillars. A long narrow belt of insulating material is wound around two pulleysP1andP2.B1andB2are two sharply pointed metal combs.B1is called the spray comb andB2is called the collecting comb.
Working The spray comb is given a positive potential by high tension source. The positive charge gets sprayed on the belt.
As the belt moves and reaches the sphere, a negative charge is induced on the sharp ends of collecting combB2and an equal positive charge is induced on the farther end ofB2.
This positive charge shifts immediately to the outer surface of S. Due to discharging action of sharp points ofB2, the positive charge on the belt is neutralized. The uncharged belt returns down and collects the positive charge from B1, which in turn is collected byB2. This is repeated. Thus, the positive charge on S goes on accumulating. In this way, voltage differences of as much as 6 or 8 million volts (with respect to the ground) can be built up.YES , van de graff generator only be charged up to a limit when electric field around it, is less than the breakdown field of the surrounding air which is equal to 3X 106V/m. The moment the potential of spherical shell exceeds this value, air surround it is ionisedand leakage of charge starts.