Question

Van de Graff generator is used to:
A.)Store electrical energy
B.)Build up high voltage of few million volts
C.)Decelerate charged particle like electrons
D.)Both (a) and (b) are correct.

Answer 1

Hint- To produce high voltages of an order of a few million volts, the Van de Graff generator is used. This results in large electrical fields being generated for experimental purposes.

Complete step-by-step answer:
Principle - A Van de Graff generator is a traveling belt generator that accumulates electrical charge on a hollow metal globe on an insulating column, generating incredibly high potential. At low current it produces very high direct voltage (DC) electricity.

The charge on the roller is much more concentrated than the charge on the belt and because of this concentration of charge the roller’s electric field is much stronger than the belt’s at the location of the roller and lower electrode.

As we know that the metals are good conductors of electricity and positive ions easily surround them. Now the brush assembly has wire tips that are charged positively as the electrons have shifted away from the tips, into the motor housing contact. If an atom is stripped of its electrons, the fourth state of matter is called plasma. Therefore we have free electrons and positive charged air molecules between the roller and the brush. The electrons repel from the roller and bind to the tips of the electron less brush thus attracting the positive atoms to the negatively charged roller. The positively charged atomic nuclei from the air molecules are attempting to push into the roller that is negatively charged, but the belt is in the way. And now the belt is "coated" with the positive charge which it takes away from the roller afterwards.

The Van de Graaff generator will continue to charge the belt, as long as there is air between the lower roller and brush assembly.

From the above it is clear that the van de Graff generator is used to build up high voltages of few million volts.
Hence the correct option is B.

Note- Van de Graff generators on a small scale are used for exhibitions in science centres or projects. On a bigger scale van de Graff generators are enclosed in vacuum or inert gas chambers so that the high voltage produced does not ionize nearby gas atoms. Such generators produce more than 10 megavolts. And thus at this potential electrons can be made to accelerate at high speed. Such setups are used to produce x-rays, and used in medicine science and also to preserve food. Proton generators are used in nuclear physics.