B and H field for a long rod and a disk

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Discussion Overview

The discussion revolves around the magnetic fields (B field and H field) associated with a long rod and a disk that have uniform magnetization (M). Participants explore the implications of magnetization on these fields, particularly in the context of boundary conditions and demagnetization effects.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks help in determining the B and H fields for a rod and a disk with uniform magnetization, indicating a lack of understanding of the problem.
  • Another participant notes that magnetization relates to the H field through a factor of susceptibility and suggests that the B field can be derived from this relationship, asking for more context on the original question.
  • A participant introduces the concept of demagnetization and mentions that the demagnetizing factor is uniform for an ellipse.
  • One participant provides specific values for B and H fields for both the disk and rod, stating that boundary conditions at the surfaces are crucial, and mentions that permeability and susceptibility are not applicable in this case.
  • Several participants inquire about the meaning of "BC," which is later clarified as "Boundary Conditions," specifically noting the continuity of B and H at the surfaces.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the interpretation of the problem or the implications of the boundary conditions. There are competing views regarding the significance of the boundary conditions and the applicability of certain concepts.

Contextual Notes

There is uncertainty regarding the assumptions made about the uniformity of magnetization and the specific conditions under which the B and H fields are calculated. The discussion also highlights the dependence on boundary conditions, which may not be fully resolved.

runnerwei
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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?
any reply highly appreciated.
 

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    magnetiszation.png
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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 [tex]\chi[/tex].

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.
 
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?
 
Meir Achuz said:
.
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?
 
Boundary Conditions: B_normal continuous, H_tangential continuous.
 

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