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VAN DE GRAAFF       GENERATOR                            SUBMITTED BY: Victor Chowdhury                                   ...
INTRODUCTION :   A Van de Graaff generator is an electrostatic generator    which uses a moving belt to accumulate very h...
VAN DE GRAAFF GENERATOR:                 A Van de Graaff                  generator is an              electrostatic machi...
CONSTRUCTION :Van De Graaff Generator consist of   1) hollow metal sphere   2) upper electrode   3) upper roller (metal...
DESCRIPTION : A simple Van de Graaff-generator consists of a belt of silk, or a similar flexible dielectric material, runn...
WORKING PRINCIPLE :    As the belt passes in front of the lower comb, it receives negative     charge that escapes from i...
APPLICATION :   They are used where a very high voltage at very    low current is needed.   The beam of these charged ac...
References:   http://en.wikipedia.org   Zavisa, John M.. "How Van de Graaff    Generators Work". HowStuffWorks.    Retri...
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Ven de graaff generator 745

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As the belt passes in front of the lower comb, it receives negative charge that escapes from its points due to the influence of the electric field around the lower pulley, that ionizes the air at the points. As the belt touches the upper roller (3), it transfers some electrons, leaving the roller with a negative charge (if it is insulated from the terminal), which added to the negative charge in the belt generates enough electric field to ionize the air at the points of the upper comb. Electrons then leak from the belt to the upper comb and to the terminal, leaving the belt positively charged as it returns down and the terminal negatively charged. The sphere shields the upper roller and comb from the electric field generated by charges that accumulate at the outer surface of it, causing the discharge and change of polarity of the belt at the upper roller to occur practically as if the terminal were grounded. As the belt continues to move, a constant charging current travels via the belt, and the sphere continues to accumulate negative charge until the rate that charge is being lost (through leakage and corona discharges) equals the charging current...............The larger the sphere and the farther it is from ground, the higher will be its final potential.

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  1. 1. VAN DE GRAAFF GENERATOR SUBMITTED BY: Victor Chowdhury ROLL: 090190325 Batch: 5th SUBMITTED TO : MR. RIKU CHOWDHURY FACULTY OF SCIENCE, LECTRUR, FSET, USTCENGINERING AND TECHNOLOGY
  2. 2. INTRODUCTION : A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high electrostatically stable voltages on a hollow metal globe on the top of the stand. It was invented in 1929 by American physicist Robert J. Van de Graaff. The potential differences achieved in modern Van de Graaff generators can reach 5 megavolts. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a capacitor and a very large electrical resistance SHORTLY : Its a device that generates static electricity on a moving belt and transfers it to a collector sphere.
  3. 3. VAN DE GRAAFF GENERATOR: A Van de Graaff generator is an electrostatic machine which uses a moving belt to accumulate very high electrostatically stable voltages on a hollow metal globe. The potential differences achieved in modern Van de Graaff generators can reach 5 megavolts.
  4. 4. CONSTRUCTION :Van De Graaff Generator consist of 1) hollow metal sphere 2) upper electrode 3) upper roller (metal) 4) side of the belt with positive charges 5) opposite side of the belt with negative charges 6) lower roller 7) lower electrode (ground) 8) spherical device with negative charges, used to discharge the main sphere 9) spark produced by the difference of potentials
  5. 5. DESCRIPTION : A simple Van de Graaff-generator consists of a belt of silk, or a similar flexible dielectric material, running over two metal pulleys, one of which is surrounded by a hollow metal sphere.[1] Two electrodes, (2) and (7), in the form of comb-shaped rows of sharp metal points, are positioned respectively near to the bottom of the lower pulley and inside the sphere, over the upper pulley. Comb (2) is connected to the sphere, and comb (7) to the ground. A high DC potential (with respect to earth) is applied to roller (6);
  6. 6. WORKING PRINCIPLE :  As the belt passes in front of the lower comb, it receives negative charge that escapes from its points due to the influence of the electric field around the lower pulley, that ionizes the air at the points. As the belt touches the upper roller (3), it transfers some electrons, leaving the roller with a negative charge (if it is insulated from the terminal), which added to the negative charge in the belt generates enough electric field to ionize the air at the points of the upper comb. Electrons then leak from the belt to the upper comb and to the terminal, leaving the belt positively charged as it returns down and the terminal negatively charged. The sphere shields the upper roller and comb from the electric field generated by charges that accumulate at the outer surface of it, causing the discharge and change of polarity of the belt at the upper roller to occur practically as if the terminal were grounded. As the belt continues to move, a constant charging current travels via the belt, and the sphere continues to accumulate negative charge until the rate that charge is being lost (through leakage and corona discharges) equals the charging current...............The larger the sphere and the farther it is from ground, the higher will be its final potential.
  7. 7. APPLICATION : They are used where a very high voltage at very low current is needed. The beam of these charged accelerated particles is used to trigger the nuclear reaction . In medicine, such beams are used to treat cancer. Accelerated particle beams are used to break atoms for various experiments in physics .
  8. 8. References: http://en.wikipedia.org Zavisa, John M.. "How Van de Graaff Generators Work". HowStuffWorks. Retrieved 2007-12-28.
  9. 9. THE END.
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