MadSci Network: Physics

Re: Do magnets act differently in a vacuum?

Date: Wed Jan 21 13:32:54 2004
Posted By: Guy Beadie, Staff, Optical sciences, Naval Research Lab
Area of science: Physics
ID: 1073846351.Ph

Wow Ė thatís an interesting question!  Why?  Because it makes me think 
about what a magnet really is and how it works.

The answer your question,

ďDo magnets act differently in a vacuum?Ē


ďNo, they donít.Ē  Of course, that isnít a very helpful answer.

A good answer would explain Ďwhyí a magnet in vacuum behaves the same and, 
if possible, would describe some way that a magnet _does_ change.  Iíll do 
my best to give you such an answer.

A permanent magnet is a magnet because of the way tiny little pieces of it 
behave, together.  In most materials the little pieces (electrons) align 
themselves in all different directions.  In magnets, however, these pieces 
line themselves up like teeth on a comb or bristles on a brush.

Now, each one of the electrons acts like a tiny magnet.  When they donít 
line up, like in most materials, all the little electronic magnets cancel 
each other out.  On the other hand, when they all line up the combined 
effect makes for a big magnet.

This is why a magnet will still be a magnet when you place it in a vacuum: 
removing air from outside the magnet doesnít change the alignment of the 
electrons inside.

So, what might change a magnet if a vacuum wonít?  It would have to be 
something that flips the little electrons inside a magnet.  Turns out, 
magnets interact with other magnets.  You can see that yourself if you get 
a chance to play with two magnets Ė they will pull themselves together or 
push themselves apart, depending on how they line up with one another.  
Since magnets act upon one another, it stands to reason that a really 
strong magnet might change a weaker one.

You can see this effect directly if you have a floppy disk.  Computers are 
moving more and more towards optical CDs for data storage, but itís still 
likely that youíve used floppy disks.  Floppy disks store information 
magnetically: information is stored on the disks as little magnetized 
regions that point either up or down.  Take an empty disk, and save a file 
on it.  After you remove the disk from the drive, put the disk near a 
strong magnet (such as a good refrigerator magnet).  If you now try to 
read the disk, youíll find that the computer no longer recognizes any of 
the information: the strong magnet realigned the weaker magnets that 
provided the fileís information.

Another way to change a magnetís strength is through temperature.  If you 
heat up a magnet, it will become a weaker magnet.  If you cool one down, 
it will become a stronger magnet.  Thatís because heating something up 
causes all the little pieces in the material to shake a lot.  If all the 
little magnets are shaking in different directions, then theyíll no longer 
add up to make a big magnetic field.  If they get too hot, each one will 
actually spin all over the place, completely wiping out the magnet.  On 
the other hand, if you cool the magnet down, the little magnets that were 
spinning around lock back into alignment with one another and eventually 
settle down to a very ordered, very magnetic state.

Unfortunately, it isnít likely that youíll be able to test this yourself.  
Most of the effects arenít noticeable unless the magnets are _really_ hot 
or _really_ cold, so it isnít practical to check them out in a normal 
household setting.

Hope this answers your question,

-	Guy

PS  Here are some web resources for finding out more about magnetism.  I 
should point out that I had a very hard time finding good sites that 
explain magnetism for non-scientists.

One reason for that, I think, is that even the smartest scientists in the 
world still cannot explain why the little, electron magnets behave the way 
they do.  So if youíre struggling with the concepts of magnetism donít 
fret: some of the smartest people in the world are too!

Here is also a site which provides little web videos for educational 
purposes.  Their magnetism video is quite good, but the download process 
can be slow, and Iíve had occasional trouble with connection:

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2003. All rights reserved.