Van de Graaff Generator 8 9 Schematic view 6 5 Proton Neutron Electron 4 7 3 2 1 • A Van de Graaff generator is made by a belt of a flexible insulating material, running over two rollers (wheels), one of which is surrounded by a hollow metal ball. 1.Power Supply that pulls off electrons. 2, 4. Rollers. 3. Positively charged belt (lost some electrons) • Metal comb that drops electrons from the ball onto the belt. • Metal ball that gives up electrons to the belt, then it is charged! • Negatively charged belt (gained some electrons from the ball). 8. Grounding wand, it can give or take electrons to make everything even again. • Discharge: A spark, a flow of electrons through the air. • The bigger the ball, and farther from the ground it is lets you build more charge up on it.
Van de Graaff Information • The fundamental idea of friction machine as high voltage supply traces back to 17th Century. • Generator invented to supply the high energy needed for early particle accelerators. • The first model was demonstrated in October 1929, using a silk ribbon bought at a five and dime store as the charge transport belt. • Originally used as a research tool in early atom-smashing and high energy X-ray experiments. 1931, Robert J. Van de Graaff (left) poses with his electrostatic generator and Karl T. Compton, MIT president The largest VDG generator, on display at the Boston Museum of Science