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Q & A: magnets

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Most recent answer: 03/04/2009
Q:
I have a few questions about magnets. 1. How strong could you make a permanent magnet that was made out of iron that was 6 x 12 x 2 in.? (What i mean is, what is the max weight that a magnet could pull 1 inch away from the object it is trying to pull?) 2. If you were to have 2 permanent magnets facing opposite poles that were atracted to eachother? (for ex. +##- +##- ) Would these two magnets stay magnetized almost indefinitely?
- Paul (age 17)
San Saba, Tx, USA
A:
Let me answer #2 first.

If you have two permanent magnets facing the way you’ve shown, with the north pole of one pressed against the south pole of the other, together they just make one big permanent magnet. If they were good permanent magnets to begin with, their little magnetic domains will stay lined up "almost indefinitely". That won’t change in the combined magnet.

Your question is a good one, because if you forcibly lined up the magnets the other way (north touching north) the forces between them would pushing the domains toward changing their directions. Then the magnets wouldn’t last quite as long.

On your first question, the answer depends on exactly how strong the permanent magnet is, and the shape and magnetic properties of the thing it’s being used to pick up. Of course, even if you told me those things the precise calculation would be hard. Using a rough estimate of how strong a standard magnet is, however, I’d guess you could pick up about four pounds. Maybe it would be two pound or eight pounds- why not try the experiment?

Mike W.

(published on 10/22/2007)

Follow-Up #1: magnet dangers

Q:
in theory, if i had two giant magnets placed at opposite polarities, twenty feet apart, could the attraction be strong enough to injure a person caught in medio?
- joseph e.shannon (age 82+)
dittmer, mo usa
A:
It sure could. There have been serious injuries caused when magnetizable things (say steel chairs) got sucked in to the big magnets of MRI machines.

Mike W.

(published on 03/04/2009)

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