Van De Graff Generator:

Concepts:  

1.	Types of charges
Protons (+)ve & electrons (-)ve
2.	Static charge	
A build-up of either type of charge

In the electrostatic machine known as the Van De Graaff 
generator, a motor-driven roller drives a belt of 
insulating material within a column of the machine.  
Positive charge collects on the roller, and an equal amount 
of negative charge collects on the inner side of the belt.  
At the base of the column, where the belt passes the 
sharp points of a charged metal "comb" this positive 
charge attracts negative charges (electrons) from the 
ground. The charged belt moves upward into a large, 
hollow, conducting dome.  Here a conducting wire, 
connected to a comb of sharp points near the top of the 
belt, allows the negative electrons from the charged belt 
to flow to the dome, making the charge on the dome 
negative. Since the dome is a conductor, its excess 
charge resides only on the outside surface.

Experiment:

When a person, insulated from ground, touches the 
conducting surface, charges are transferred to them.  
The person's hair follicles are charged, and since like 
charges repel one another, will stand up.     



Q) Does the surrounding air in any way affect the charge 
buildup on the Van De Graff generator's sphere?

Q) Do you think there is a limit of charge build-up on the 
generator's sphere?

Q) Why is it important for the person touching the 
sphere to be insulated from the ground?