Some questions on magnetic fields in matter

[springo]

Hey,

So I have a few questions because I don't understand some of the theory behind magnetism in matter.

First, I have studied electric fields in matter and it seems logical that dielectrics get attracted to regions with higher field, because they're polarized and this creates the usual electric force. However, I don't understand why diamagnetics are repelled and paramagnetics and especially ferromagnetics are attracted.

Secondly, in a magnetic circuit with an air gap, for instance a torus with a segment missing, are the two ends of the torus attracted to each other?

Finally, in a magnetic circuit, such as the one mentioned in the previous question, if you wanted to calculate the magnetic field created by the leaks in the air gap, how could you do it?

Thanks a lot for your help.

PS: This is more of a coursework thread so I didn't use the template because it was not covenient.

 

[springo]

Bump for help :)