Van de Graaff Generator - PowerPoint PPT Presentation

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Van de Graaff Generator

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Van de Graaff Generator
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Van de Graaff Generator

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  1. Van de Graaff Generator 8 9 6 5 4 Schematic view 7 3 2 1 • A Van de Graaff generator is made by a belt of a flexible dielectric 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. Document Title/Description

  2. History • 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 Document Title/Description

  3. Recent Developments • Tandem Van de Graaffaccelerator • Contains one or more Van de Graaff generators. • Negatively charged ions are accelerated through a potential difference then stripped of electrons and accelerated again. • Pelletron • Belt is replaced by a chain of short conductive rods connected by insulating links. • Air-ionizing electrodes are replaced by a grounded roller and inductive charging electrode. • Can be operated at much higher velocity than a belt, so both the voltage and currents attainable are higher than a conventional Van de Graaff machine. The largest VDG generator, on display at the Boston Museum of Science Document Title/Description