Humberto Garza
Mr.Demirturk
Physics
25 February 2014
Origin of Electricity: The Wimshurst Machine
The past three centuries many scientists have been working and making research about static electricity. Everythin start with Thales around 300BC in Greece when he was cleaning his amber, and at that time he discovered that amber rubbed with animal fur attracted light objects. This caused Thales to record his findings, and create a lot of interest and mystery towards static energy. It is important to mention that during that time, magnetism was confused with static energy. With the past of the years, things were changing for the best. In 1660 a German scientist named Otto Von Guericke built the first electric generating machine. In the experiment he showed that electricity could be transmitted by using a wet string to conduct electricity several feet.
In 1752 Benjamin Franklin made his famous experiment about the kite. During an storm, Franklin flew a kite with a stiff wire pointing up that was attached to the top of the kite. He attached a metal key to the other end of stirring and let it hang close to a Leyden Jar. With this experiment Franklin prove to the world that electricity and lighting were the same thing, also proved that pointed rods conduct electricity better than balls. Thanks to this experiment, Franklin create lighting rods and sold them throughout colonial America.
Related with static energy. In 1880 in Britain James Wimshurst create the Wimshurst machine who's major purpose is to generate high voltages. This is the most recent experiment related with static energy. Thanks to James Wimshurst the effects and results of static energy can be prove. Physics teachers and students, still used it to learn more and more about static energy.
The machine still works with just one disk turning, if the other is stopped and kept charged in some way. This idea is the base of the older machines of Holtz Voss and others, that use a rotating disk and a fixed disk with inductor plates. The elegant design of the Wimshurst machine uses the same disks to generate new charges and to induce charges, and keeps all the parts of the disks alternating polarity twice at each turn. This is important to avoid charge buildup at the unused sides of the disks, what in the machines with fixed inductors eventually reduce the induction effect and may cause periodical polarity reversals. The top and bottom of the machine operate at relatively low voltages, due to the opposite charges in the disk sectors at opposite sides. This reduces losses to the supporting structure and allows the upright supports, belts and pulleys to be positioned much closer to the disks than in other machines. At the sides of the machine, the disk sectors are charged with equal polarities, and far from the influence of the other side of the machine. A very high voltage appears, because the same charges generated at the top and bottom of the disks, where there is significant capacitance between oppositely charged sectors, are now widely separated, with low capacitance between them.
In conclusion, The Wimshurst machine is an "influence machine", an electrostatic generator that uses the charges already present on it to generate more charges by electrostatic induction. It does not rely on friction for its operation. Consider that the machine is charged as in the schematic representation, shown (with cylinders instead of disks) with each half of each disk with one polarity, with boundaries at the neutralizing bars. Ignore the charge collectors and the output circuit. The two neutralizer bars are shown floating, but it makes no difference in the operation if they are grounded. At top and bottom, the charges are opposite, and at the sides equal. With any small initial charge unbalance, the machine will quickly fall into this configuration. After this occurs, when a sector touches a neutralizing brush charge is attracted to it, with polarity opposite to the charges at the other disk, due to the influence of the electric field generated by the surrounding sectors. Since there are several sectors inducing charge in just one sector, more charge than is present in each of the opposite sectors is attracted, provided that the disks and sectors are at sufficiently small distance. The effect is that progressively larger charges are attracted to the neutralized sectors as the disks turn, and the voltages at all fixed sector positions grow exponentially. The buildup stops when the charge density on the sector surfaces creates an electric field intense enough to cause breakdown in the air around, usually just before they reach the neutralizing brushes.