Van de Graaff generator by ahmad zahid

THIS PPT WILL GIVE ALL YOU ALMOST ALL BASIC INFORMATION ABOUT VAN DE GRAAFF GENERATOR

1. CENTRAL UNIVERSITY OF KASHMIR DEPARTMENT OF PHYSICS Van de graaff generator PRESENTED BY ZAHID NISAR (1517CUK mr 029)

2. OUTLINE INTRODUCTION INVENTION PRINCIPLE CONSTRUCTION WORKING APPLICATIONS LIMITATIONS VIDEO CLIP FOR VAN DE GRAAFF GENERATOR

3. INTRODUCTION Van De Graff generator is used to generate high potential differences of near about million volts . The high voltages generated by the generator can be used for accelerating subatomic particles to high speeds, making the generator a useful tool for fundamental physics research. SOURCE: INTERNET

4. INVENTION Invented in 1929 by American physicist Robert J. Van de Graff at Princeton University, with help from colleague Nicholas Burke. SOURCE: INTERNET

5. PRINCIPLE Uses two principles of Electrostatics Corona Discharge :- Discharging action of sharp points, i.e., electric discharge takes place in air or gases readily, at pointed conductors. If the charged conductor is brought in to internal contact with a hollow conductor, all of its charge transfers to the surface of the hollow conductor and scatters uniformly over it no matter how high the potential of the latter may be.

6. Hollow metal sphere Upper electrode Upper roller (metal ) Side of the belt with positive charges Opposite side of the belt with negative charges Lower roller Lower electrode (ground ) Spherical device with negative charges, used to discharge the main sphere Spark produced by the difference of potentials. Motor which rotates the lower roller. construction 1 2 3 4 5 6 7 8 9 1

7. 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. WORKING

8. They are used where a very high voltage at very low current is needed. Used to accelerate projectiles like proton, deuteron etc. to carry out different nuclear reactions. In medicine, such beams are used to treat cancer. Used to study collision experiments in physics. APPLICATIONS

9. It produces very low intensity of current as compared to voltage. Maintenance and construction is costly and bulky. For air, a maximum of 3 million volt can be generated as after that air will ionize. It cannot accelerate neutral particles. LIMITATIONS

10. VIDEO CLIP FOR VAN DE GRAAFF GENERATOR SOURCE:YOUTUBE This link gives a video about Van De Graaff Generator that how the generator works –(https :// youtu.be/Xqt2gAalV4Y)