Question

Explain the construction and working of Van-de-Graff generator. State its uses.

Answer 1

Van-de-Graff generator: It is a machine which produces electricity of about ${10}^7$ or more potential difference.
(a) Construction: It consists of a large metallic sphere $S$ mounted on high insulating support $PP$ about $15$ on high. An endless insulating belt made up of rubber or silk passes over the pulleys $P_1$ and $P_2$. A machine rotates $P_1$, $C_1$ and $C_2$ are two metallic combs called spray comb and collecting comb respectively. $C_1$ is connected to the positive terminal of a high tension battery while $C_2$ is connected to $S$. To prevent the leakage of charge the generator is put inside the large enclosed filled with gas at $15$ atmospheric pressure. This iron enclosure is connected to earth.
(b) Working: The comb $C_1$ is connected to the positive terminal of the battery, therefore the surface density of the point becomes very high which causes wind charges on the belt. The collecting comb $C_2$ is induced negative charge and outer surface of sphere positive charge. The negative charge wind of $C_2$, cancel the positive charge of the belt. Thus, by the repeated actions more and more positive charge is induced on sphere, hence its potential increases to about ${10}^7$ volt or more.
Uses:
(i) To generate high voltage.
(ii) To accelerate $\alpha$ particles, protons and dentrons etc in nuclear disintegration.