Mad Teddy's Van de Graaff machines

Mad Teddy's web-pages

Van de Graaff machines


If you've come here by way of my High-voltage projects sub-menu , you will have seen my warnings on electrical safety. If you haven't read this yet, please click on that link and do so before proceeding.

At the time of writing (May 2005), the title of this page is something of a misnomer, if the truth be told. I've currently only got one Van de Graaff machine, made way back in 1967; and that one wasn't a great success. (The sole menu item at the bottom of this page leads to a description of this project; I hope to add more in the not-too-distant future.)

To my way of thinking, Van de Graaff machines are somewhat comic-looking things, in a vaguely alarming kind of way. You may have seen one in school. The standard experiment is to get some student to stand on an insulating platform (the term "plinth" from 1980's computer adventure games springs to mind ), and put one hand on the dome of the device while the teacher switches the motor on. The high-voltage charge which builds up makes the subject's hair stand on end, much to the amusement of the class. Bill Beaty's Van de Graaff page shows him doing this; he has longish hair and the effect is quite spectacular. (Have a look around Bill's site; he's an interesting character and his pages are very informative, as well as being quite amusing.) This site has a Quicktime movie featuring a girl with long hair undergoing a startling transformation caused by one of these machines, to considerable hilarity from onlookers.

Another experiment you can do is to put some breakfast cereal on top of the dome before switching on, as shown in the Quicktime movie on this page. (School cleaners must hate teachers who do silly things like this!)

Dr. Robert J. Van de Graaff (1901-1967) was the inventor of the high-voltage generator which has come to be named after him. From articles I have read and pictures I have seen of the good doctor (like the one on this page ), I gather that he had a playful approach and was a popular lecturer.

For all the fun and games, though, Van de Graaff machines have had an important rôle in physics. The very high voltages which can be generated are valuable for research into nuclear reactions and related matters. Although small machines are usually considered fairly harmless, the big ones can pack a wallop. (Follow the links on that last page mentioned above for an excellent history of these devices, and to see some pictures of the big one built at MIT by Dr. Van de Graaff himself.)

This page is part of a website run by an authority on electrostatic machines of all kinds. He has built twin VDG units rather like Dr. Van de Graaff's own original machine (see the previous link above), although somewhat smaller. There are some interesting links to historical belt-driven predecessors of the modern VDG.

Here are some links to various sites, some giving further historical background, some dealing with how these machines work, and some detailing models built by experimenters:

(The last link above deals with the "triboelectric series", which describes how physical contact between different substances can cause positive or negative charges to be acquired by those substances. This is important with reference to materials used for the belt and the rollers in a Van de Graaff machine; however, it also has applications in other, more general, contexts.)

Don't think that this list is exhaustive! There's lots of stuff on the internet about high-voltage projects in general, and Van de Graaff machines in particular. Use a good search engine, and have a dig around yourself to find plenty more!



My first attempt at a Van de Graaff machine

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