Tube Magnet's Magnetic Field: Effects and Questions

[healey.cj]

Hey,

How does a Tube Magnet's magnetic field differ from that of a normal bar magnet?
What effect does the cylinderical shape and the hole through the center have on the the magnetic field.

Also, i was wondering: If you were to put a long iron rod (round) through the center of a tube magnet and held the rod, what would the magnet do? Would it simply stick to the iron or would the competing magnetic forces 'balance' the magnet so that it would center itself around the rod with an equal gap between the magnet and the rod?

------o==o------- (magnetic tube with the rod through it. You'd hold the ends of the rod)

?

Thanks everyone who answers!
Chris :-)

 

[Danger]

I have no idea, but that's one very cool question. I can't wait to see what the experts come up with.

 

[Hootenanny]

What you are referring to there is known as a Halbach cylinder. It is possible to have a number of field orientations, depending on how the cylinder is magnetised. It is possible to have a zero field inside the cylinder with all the field outside. Or all the field concentrated inside the bored and non outside. Obviously we are ignoring end effects here. One application of these cylinders are in brush less motors, but if you Google I'm sure you can find much more information.

 

[healey.cj]

http://en.wikipedia.org/wiki/Halbach_cylinder

Thats the wikipedia site i found on it incase anyone is interested. Thanks Hootenanny, i had no idea what they were called...
Chris :-)