# B and H field for a long rod and a disk

As shown in the figure attached.
If both have the magnetization M, what will the B field and H fied for each object look like? why?
I have no hint how to answear this question, can anyone help?

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Usually we speak of magnetization as being inside of some material. That directly relates to the "H field" (or magnetic field inside a medium) by a factor $$\chi$$.

The "B field" then follows directly from that using basic relations; however, can you provide more context? Why do you ask?

It is something related to the concept demagnetization.
For a ellipse, the demagnetizating factor is the same everywhere.

Meir Achuz
Homework Helper
Gold Member
I assume that the picture means that M is constant in the material with the direction shown.
B and H are determined by the boundary conditions at the surfaces and constrained by the relation B-H=4pi M (in gaussian units).
Permeability and susceptibility are meaningless for this case.
For the disk, B=2pi M and H=-2pi M, because the BC at the ends dominates.
For the rod, B=4pi M and H~0 for most of the length, but near the ends the disklike BC dominates.

What dose BC mean?

.
For the disk, B=2pi M and H=-2pi M, because the BC at the ends dominates.
For the rod, B=4pi M and H~0 for most of the length, but near the ends the disklike BC dominates.
What dose BC mean?

Meir Achuz