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Q & A: magnet questions

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Most recent answer: 09/18/2018
Q:
My daughter is working on a science fair project, and needs to consult with an expert on magnets. We would appreciate any help you can give us. To the department of physics I am look in for help on my science fair project. I had a few questions about magnets. Here are my questions:What causes a megnets strength to change?Is it possible to make a magnet stronger?Are the north and south sides of a magnet of the same strength?What is the best way to test a magnets strength.Thank you for whatever help you can offer.
- Jenny (age 42)
Omaha, NE, USA
A:

1. Lots of things can change the strength of a magnet. They'll generally get weaker if heated. They usually get weaker if they are struck hard with a hammer or something. Sometimes they'll get a little stronger when cooled.

How do these work? Some work by scrambling the orientation of the little magnetic domains that have to be lined up to maximize the strength. Some (heating) also weaken the strength of the individual domains by scrambling up he directions of the individual magnetic moments of the electrons in them.

2. You may be able to make a magnet a little stronger by heating it and cooling it in the field of a very strong electromagnet. That's not very practical at home. 

3. If the shape of the bar or horseshoe magnet is symmetrical, the N and S ends are the same strength. If one is wider than the other, its magnetic fieldis weaker but more spread out. There are other forms of magnets with more complicated pole patterns. For example, there are donut-shaped magnets where the fields just go around a loop, without any poles.

4. There are many ways to test a magnet's strength. Commercial Gaussmeters, whichoften use the effect of magnetic fields on the direction of current flow, are one easy way. For something cheap at home, you can try seeing how long a chain of paperclips the magnet will hold up.

Mike W.


(published on 09/18/2018)

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