Van De Graaff Generator

Introduction to Van de Graaff generator:

Let us learn about the van de Graaff generator. Van de graaff generator produces a continuous supply of charge on a large metal dome when a rubber belt is driven by an electric motor or by hand which is show in the figure. For example pens and combs made of certain plastics become charged when rubbed on your sleeve and can then attract scraps of paper.

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Positive and Negative Charge:


When a strip of polythene is rubbed with a cloth it becomes c harged. If it is hung up ans another rubbed polythene strip is brought near, repulsion occurs. Attraction occurs when a rubbed strip of cellulose acetate approaches.

This shows there are two kinds of electric charge. That on cellulose acetate is taken as positive (+) and that on polythene is negative (-). The force between electric charges decreases as their separation increases.


Demonstrations:


Let us see the demonstration of Van de Graaff generator. In our figure a, sparks jump between the dome and the discharging sphere. Electrons flow round a complete path from the dome. In part b why does the ‘hair’ stand on end? In part c the ‘windmill’ revolves due to the reaction that arises from the ‘electric wind’ caused by the action at points effect, explained above for the lightning conductor.Is this topic Average Speed Formula hard for you? Watch out for my coming posts.



Action:

Let us see the action of Van de Graaff generator. Initially a positive charge is produced on the motor-driven Perspex roller due to it rubbing the belt. This induces a negative charge on the ‘comb’ of metal points P, in figure a, which are sprayed off by ‘action at points’ on to the outside of the belt and carried upwards. A positive charge is then induced in the comb of metal points Q and negative charge is repelled to the dome. This concept will clearly explained you to know about the Van de graaff generator.