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Fun with an MRI magnet

By: practiCalfMRIPublished: 6 years ago

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In honor of MRI Safety Week, four simple demonstrations of induced magnetism in non-ferromagnetic objects, and one demonstration of an unlikely magnetic object. Apologies for the awful sound quality, it's a new MRI facility and we don't yet have all the sound-proofing up to eliminate the echoes. And we were in a hurry.

First, a copper ring is accelerated under gravity, inducing a current and an opposing magnetic field in the ring that makes it float down rather than fall. Next, an aluminum ball can be easily placed inside the MRI magnet, but it can't be thrown in! The faster the ball is accelerated the larger the induced field opposing the motion!

Then we move onto tests with money. Non-magnetic coins (a quarter and a nickel) will spin easily outside the high magnetic field region, but the spin is inhibited inside the high field regions, again because of induced magnetism opposing the spinning motion.

And finally, a dollar bill makes an unlikely magnet. But roll it into a tube and it'll get tugged inside the MRI magnet by virtue of the very low amount of ferromagnetic ink it contains. (This experiment works just as well with $5, $10 and $20 bills, but the chances of the note vanishing inside the magnet bore increase with the denomination!)

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