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Q & A: Magnets in liquids

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Most recent answer: 10/22/2007
Q:
can magnets work under ANY liquid?
- christine (age 12)
north america
A:
Permanent magnets, like bar magnets and horseshoe magnets, create magnetic fields regardless of their surroundings. Many common substances (water, wood, most plastics, some metals) have very weak magnetic properties, and the magnetic fields penetrate them nearly unchanged. Some materials affect the magnetic field quite a bit. Iron nails, for instance, draw magnetic field lines towards them, where they travel for a bit, and then come out the other side on their way to the other pole of your magnet. Putting an iron bar across the poles of a horseshoe magnet will weaken the magnetic field far away from the magnet because more of it goes through the iron bar and less to farther places.

Some liquids have similar effects. You can make a liquid consisting of a suspension of small iron filings in a gooey fluid (water won't work -- the iron will just settle out to the bottom). Gooey oil might do the job better. This liquid acts a lot like the iron nail above. If you put a magnet close to the surface of the liquid, a little hill will form on the surface as bits of the liquid are attracted to the magnet, while gravity wants to hold it down. If you immerse the magnet in such a liquid, more of the field lines will want to stay within the liquid than escape, so you might say that the magnet isn't "working as well" (even though it is, it's just the liquid getting in the way of the magnet's field far away). You may have a tough time cleaning this liquid off of your magnet (it's gooey and the magnet likes to stick to it).

Tom

(published on 10/22/2007)

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