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Q & A: Does magnetism travel through all materials?

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Most recent answer: 11/17/2012
Q:
Does magnetism travel through all materials?
- Gabby (age 9)
Blue Bell, PA 19422
A:
There are some materials that magnetic fields can't enter. Most superconductors won't let a magnetic field in more than a tiny distance. So if you want to shield something from magnetic fields, you can put layers of superconductor around it. You have to keep them cold enough to stay superconducting. In our lab we've done that occasionally with thin sheets of lead or niobium. If the field gets too strong, however, it causes loss of the superconductivity. Depending on the type of superconductor, the whole thing may then just quit superconducting and let field in or little tubes of field may go through non-superconducting regions.

There are other materials which attract magnetic fields, sort of pulling the field into the material. Although that's the opposite of how the superconductors act, it can also be used to shield things. If you surround something with one of these "mu-metals" the magnetic field will mostly travel through the shield and not penetrate inside. We've also used this type of shield in my lab.

Some magnetic fields are not steady, but switch direction back and forth. The fields in radio waves, for example, are like that. Sheets of metal can block these "ac" waves. However, fields that change slowly enough go right through ordinary metal.

Most materials, however, don't do much to magnetic fields, which just go right through them.

Mike W.
 

(published on 11/17/2012)

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