Friday, October 26, 2007

Do You Have a Magnetic Personality?

This one was once in Scientific American.

You are in a room where there are no metal objects except for two iron rods. Only one of them is a magnet.

How can you identify the magnet? There are several possibilities. What's your solution?


  1. break it in half and see which one has magnetic properties with itself

  2. I don't think I could break 2 iron rods. Unless they're very thin!

  3. I think the easiest way would have to do with the orientation. The magnetic field of the magnetized rod would have a dipole pattern, so if you put the rods in a T-pattern on the ground, and then exchanged their positions, you should be able to tell.

    | ----

    If the rod on the right were the magnet, the rods would attract, but otherwise they would not. If the rod on the right is the magnet, it would tend to polarize the left rod in the left-right direction, and all those little magnetic dipoles would be drawn to the magnet. If the left rod is the magnet, it will not polarize the right rod because of the weakness of the field at that angle in a dipole pattern.

    I really like the compass idea, assuming you have a string or something to hang it with, but this idea should work with nothing but the two rods.

  4. Nice job Abe. lil lesley is also right, too. If you have a string (or something like that), you can hang the bars and see which one reorients itself.


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