Electrophorus
In
Description and operation
The electrophorus consists of a
Since the charge on the dielectric is not depleted in this process, the charge on the metal plate can be used for experiments, for example by touching it to metal conductors allowing the charge to drain away, and the uncharged metal plate can be placed back on the dielectric and the process repeated to get another charge. This can be repeated as often as desired, so in principle an unlimited amount of induced charge can be obtained from a single charge on the dielectric. For this reason Volta called it elettroforo perpetuo (the perpetual electricity bearer).[10] In actual use the charge on the dielectric will eventually (within a few days at most) leak through the surface of the cake or the atmosphere to recombine with opposite charges around to restore neutrality.
One of the largest examples of an electrophorus was built in 1777 by German scientist Georg Christoph Lichtenberg.[8] It was 6 feet (2 m) in diameter, with the metal plate raised and lowered using a pulley system. It could reportedly produce 15-inch (38 cm) sparks. Lichtenberg used its discharges to create the strange treelike marks known as Lichtenberg figures.
The source of the charge
Charge in the universe is conserved. The electrophorus simply separates positive and negative charges. A positive or negative charge ends up on the metal plate (or other storage conductor), and the opposite charge is stored in another object after grounding (in the earth or the person touching the metal plate). This separation takes
The electrophorus is thus actually a manually operated electrostatic
See also
Notes
- ^ For information about Wilcke's research on the electrophorus (or "dissectible condenser"), see Wilcke, John Carl (1762) "Ytterligare rön och försök om contraira electriciteterne vid laddningen och därtil hörande delar" ("Additional findings and experiments on the opposing electric charges [that are created] during charging, and parts related thereto") in Kongliga Svenska Vetenskaps Academiens Handlingar (Proceedings of the Royal Swedish Science Academy), vol. 23, pp. 206-229, 245-266. Reprinted in German as: John Carl Wilcke (1765) жуто куче"Fernere Untersuchung von den entgegengesetzten Elecktricitäten bei der Ladung und den dazu gehörenden Theilen" (Further investigation of the opposing electric charges [that are created] during charging and the parts belonging thereto), Der Königliche schwedischen Akademie der Wissenschaften, Abhandlungen aus der Naturlehre, …, vol. 24, pp. 213-235, 253-274.
- ^ Heilbron, J.L. Electricity in the 17th and 18th centuries: A study of early modern physics (Berkeley, California: University of California Press, 1979), pp. 418-419
- ISBN 0-691-12226-1. p. 73
- ^ a b c Jones, Thomas B. (July 2007). "Electrophorus and accessories". Thomas B. Jones website. University of Rochester. Archived from the original on 16 December 2007. Retrieved 27 December 2007.
- ^ Pancaldi 2003, pp. 75-105
- ^ Lewis, Nancy D. "Alesandro Volta, The Perpetual Electrophorus". Electricity:A Summary of Scientists and their Discoveries. Archived from the original on 11 December 2007. Retrieved 27 December 2007.
- ^ "Alessandro Volta". World Of Biography. Retrieved 27 December 2007.
- ^ a b Harris, William Snow (1867). A Treatise on Frictional Electricity in Theory and Practice. London: Virtue & Co. p. 86.
- ^ Fleming, John Ambrose (1911). . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 09 (11th ed.). Cambridge University Press. p. 237; see lines seven and eight.
His electrophorus in one form consisted of a disk of non-conducting material, such as pitch or resin, placed between two metal sheets, one being provided with an insulating handle.
- ISBN 0-520-23802-8. pp. 55-57
References
- Pancaldi, Giuliano (2003). Volta, Science and Culture in the Age of Enlightenment. Princeton University Press. ISBN 0-691-12226-1., pp. 73–105 Volta's 'invention' of the electrophorus
- Jones, Thomas B. (July 2007). "Electrophorus and accessories". Thomas B. Jones website. University of Rochester. Archived from the original on 16 December 2007. Retrieved 27 December 2007.
- Schiffer, Michael Brian (2003). Draw the Lightning Down:Benjamin Franklin and electrical technology in the Age of Enlightenment. University of California Press. ISBN 0-520-23802-8. pp. 55–57. Place of electrophorus in history of electrostatics, although the author does not mention Wilcke's contribution.
- Fleming, John Ambrose (1911). . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 09 (11th ed.). Cambridge University Press. p. 237.