When I magnetize water by circular magnets of strength 0.8 T, how long will the magnetism be present in the water? I mean, how many days will it be in the water?
closed as off-topic by Aaron Stevens, user191954, JMac, John Rennie, GiorgioP Feb 28 at 21:04
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The quantity you're asking for is called the "relaxation time" and is useful when performing NMR. There are many tables for this sort of thing, but just going off of Wikipedia, the atomic nuclei for water should lose their magnetization in about 1 second. The electrons, which are much more exposed, lose their magnetization even faster than that.