# Magnetization in a rod bent into a torus

1. Oct 19, 2012

### benf.stokes

1. The problem statement, all variables and given/known data

I can't figure out why there is no bound current in the problem 6 (very subtle hint boldfaced) is the pdf below:
http://astronomy.mnstate.edu/cabanela/classes/phys370/homework/ps10.pdf [Broken]

Can anybody give me a hint as to why there should be no bound current
3. The attempt at a solution

I know that the total dipole moment contained in a volume element must be constant. However i can't turn this into a relationship between the new M and the old one

Last edited by a moderator: May 6, 2017
2. Oct 19, 2012

### TSny

See if you can follow the hint. How would the mass density ρ in the bent rod vary with radial distance s? See attached picture. Let point a be a point where the density happens to be the same as the unbent rod (ρo). Can you express the density ρ at an arbitrary point b in terms of the density ρo at a and the radial distances s and so?

If you can figure that out, then you should be able to see how the magnetization M varies with s.

#### Attached Files:

• ###### Bent rod.png
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3. Oct 20, 2012

### benf.stokes

I figured it out due to your help. Thanks :)