MadSci Network: Physics

Re: how does the Van de Graaff generator produce stadic electricity?

Date: Sun May 23 15:44:30 1999
Posted By: Steven Levin, Research Scientist, Astrophysics, Jet Propulsion Laboratory
Area of science: Physics
ID: 926551257.Ph

Hi Ebere,

You can find all kinds of good stuff about Van de Graaff generators at

and it might be more helpful (certainly more thorough) than my answer.  
There are pictures and diagrams there too.  There's also some information  
intended for teachers at  and 

which you might find interesting too.

Electricity is carried around by extremely tiny particles which have 
"electric  charge".   All ordinary matter (like you and me, and the chair
you're sitting on) is made up of protons, electrons, and neutrons, which 
are so small that you can't see them.  The protons and electrons have 
electric charge, and the protons and neutrons stick together pretty 
strongly, but the electrons can sometimes move around fairly easily. By 
moving a bunch of electrons off of one object and onto another, we can  
build up extra electric charge in one place, and leave electric charge 
"missing" in the other.  That's called "static electricity", and it's what 
a Van de Graaf generator does.  There's a belt (often hidden from view) 
which rubs electrons off of the base and carries them up to the top, where 
a metal sphere collects them. The base usually picks up more electrons from 
whatever it's sitting on, so you don't notice the loss very much, but the 
metal  sphere keeps collecting more and more electrons and pretty soon you 
can see all the interesting effects.

Electrons can move around freely inside some materials (like metals) but 
are stuck wherever they land in other materials (like plastics and wood or  
cloth). The belt is usually made out of plastic or cloth, so when it picks 
up electrons they're stuck until they get up to the metal sphere, and 
escape onto the metal.  Electrons repel each other, so once they get to the 
metal sphere, they all spread out evenly over the sphere.  

There are some really cool pictures at 

and you can learn some more about electricity at


			-Steve Levin  

DISCLAIMER:  Just because I work for JPL/NASA/Caltech doesn't mean  
anything I say is in any way official.  This is just me talking, not NASA,  
JPL, or Caltech.     

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