testing magnets and silver coins
LanceNewmanOCC
Posts: 19,999 ✭✭✭✭✭
just watched someone take a fairly strong magnet and in the air above a peace dollar, move the magnet from side to side and VOILA, the peace dollar DID move while the magnet was.
anyone test this out yet? (thinking about that war nickel thread)
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Was his name David Blaine?
ok. i just tested it on some gorham silver flatware and while my magnets are kinda too strong for the fridge, they are JUST strong enough to get the forks to move when i stack them on their arches. yay
since my magnets are not impressive, i did connect a couple of them top to bottom so they are flatter and longer and then just pushed them to slide under the suspended fork and that worked too.
from what i've gathered/read/watched, 90% silver coins should NOT "stick" to magnets in general because while they react to magnetic fields, as do a lot of things we don't normally think of, it is not magnetic per se.
Silver pushes away from magnets
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Yep, silver and copper, along with some other materials, are diamagnetic...they oppose magnetisim.
"Some of the most common examples of diamagnetic substances are Copper, Zinc, Bismuth, Silver, Gold, Antimony, Marble, Water, Glass, NACL, etc..."
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If you use the Neodymium magnets, the effect of diamagnetics can be seen with a lot of 'non-magnetic' materials. Cheers, RickO
This effect which you're seeing - the silver coin is attracted to the magnet, but only when it is actually moving - is not "diamagnetism" per se - the magnetic repulsion caused by diamagnetism is usually too weak to notice. Rather, what you are seeing here is "eddy current magnetism" - the principle by which when a magnetic field moves relative to a nearby electrically conductive substance, the magnetic field creates an opposing magnetic field in that electrically conductive substance it passes next to. The stronger the field, and the faster the relative motion, the stronger the effect. Electricity generation turbines and electric motors all operate using the same principle.
Silver, being the best electrically conducting substance known, produces stronger eddy current fields than any other substance. So yes, silver coins do "dance around" on a table, when a super-powerful magnet passes above them. And yes, you can (and people have) construct a device that "tests for silver" using eddy current magnetism. Most of the eddy current testers I have seen use gravity to either move a coin past a magnet, or vice versa, and the eddy current effect generated by the silver coin is strong enough to counter gravity and "stop" the falling from taking place; a non-silver coin doesn't generate strong enough eddy currents, and so it keeps falling.
Roman emperor Marcus Aurelius, "Meditations"
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