mmm@weitek.UUCP (Mark Thorson) (08/07/85)
When I took undergrad physics in college, the department had a machine they used to demonstrate Eddy currents. It consisted of a round table on casters, about three feet in diameter and four feet high. It was made by General Electric and looked about forty or fifty years old. The teacher would put an aluminum bowl on it (about two feet in diameter and half a foot deep) and turn the machine on. The machine would hum and buzz, and the bowl would float up about half a foot. Sometimes the demonstrator would put some water in the bowl and force the bowl against the table with a stick. The Eddy currents would become very strong, the bowl would heat up, and the water would boil. What kind of magnetic field was being generated? I was told that the shape of the bowl was important, as well as the fact that the field was moving. I would like to know enough about the field and the bowl that I could build one. Pointers to articles, US patents, etc on this device would be appreciated. Mark Thorson (...!cae780!weitek!mmm)
gwyn@brl-tgr.ARPA (Doug Gwyn <gwyn>) (08/09/85)
I don't know how the eddy current magnet you saw was constructed, but one can be made as follows: --------------------------------------- --------------------------------------- ooooooooooooooooooooooooooooooooooooooo ooooooooooooooooooooooooooooooooooooooo --------------------------------------- --------------------------------------- --------------------------------------- ooooooooooooooooooooooooooooooooooooooo ooooooooooooooooooooooooooooooooooooooo --------------------------------------- --------------------------------------- (This is a cross-section of a cylindrical magnet with its axis of symmetry running horizontally. "o" is the copper wire and "-" is soft iron.) A magnet like this (actual size, using 10-pitch printout) will easily lift a quarter when powered off a hefty AC supply. This is the result of the induced eddy current in the quarter being opposite the main field of the magnet.