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Unformatted text preview: 1/18/2012 1 Lecture 3-1 Electric Field from Charges on Pointed Surfaces Now consider a sharp point . The field lines are much closer together, i.e., the field is much stronger and looks much more like the field of a point charge. E field is always perpendicular to the surface of a charged conductor Lecture 3-2 Demo - Electrostatic Wind The strong electric field at the sharp tip polarizes atmospheric molecules. If a molecule is ionized, the ion will be repelled from the point. The recoil force causes the whirl to spin. Lecture 3-3 The Van de Graaff Generator The Van de Graaff generator works by applying a positive charge to a non-conducting moving belt using a corona discharge The moving belt driven by an electric motor carries the charge up into a hollow metal sphere where the charge is taken from the belt by a pointed contact connected to the metal sphere The charge that builds up on the metal sphere distributes itself uniformly around the outside of the sphere For this particular Van de Graaff generator, a voltage limiter is used to keep the Van de Graaff generator from producing sparks larger than desired The Van de Graaff generator was invented by Robert J. Van de Graaff, an American physicist (1901-1967) Lecture 3-4 Coulombs Law (Review) q 1 q 2 r 1,2 r 2 2 9 / 10 99 . 8 4 1 C m N k = = where is called the permittivity constant....
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- Spring '08