Field due to Magnetic Materials

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Discussion Overview

The discussion revolves around the behavior of magnetic fields in the presence of magnetic materials, specifically focusing on the relationship between the applied magnetic field (H), the magnetic flux density (B), and the magnetization (M) of materials such as paramagnetic and diamagnetic spheres. Participants explore theoretical implications and practical interpretations of these relationships.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that outside a magnetic material, B and H are essentially the same, proposing that B = 10 Gauss outside the material when H = 10 Oe is applied.
  • Another participant asserts that the magnetization of the material does affect the fields outside, but maintains that B and H remain equal.
  • A different participant questions whether the magnetic field around a sphere of radius R is uniformly 10 Oe, suggesting that the sphere alters this value and inquires about the implications of H = (1/\mu_0)B - M.
  • One participant seeks clarification on whether H in the equation H = (1/\mu)B - M refers to the applied field or the total field, expressing confusion about the practical utility of this equation.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the applied field, the magnetic field, and the effects of magnetization. There is no consensus on how these quantities interact or the implications of the equations presented.

Contextual Notes

Participants highlight potential ambiguities in the definitions of H and B, as well as the role of magnetization in determining the fields outside the material. The discussion reflects uncertainty regarding the application of the equations in practical scenarios.

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Say you have a paramagnetic (or diamagnetic) sphere (or some other shape) and you apply a field of H = 10 Oe. Now, we have [itex]H=(1/\mu)B-M[/itex].

That would indicate that outside of the material, B and H are essentially the same, right? B = 10 Gauss, outside of the material.

But shouldn't the magnetization of the material affect the field outside, as well?

Certainly if these were permanent magnets it would. I would expect that in all cases we would want to integrate M over the volume of our shape, then calculate the field from that dipole moment. But these equations seem to suggest that would be zero. Or am I misunderstanding their terms?

Thanks!
 
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The magnetization of the material affects both fields outside, but B and H are still equal.
 
So let's say that I have a sphere (radius R) of permeability [itex]\mu[/itex] and I apply a field H = 10 Oe. Would it be correct to say that the field around the sphere is not uniformly 10 Oe, because the sphere changes its value? (And also correct that B = H?)

If so, what good is [itex]H=(1/\mu_0)B-M[/itex]?
 
Perhaps my question is not totally clear.

In H=(1/u)B-M, is H the applied field, or the total field, after the contributions of the magnetic material? And if it is the total field, how does this do us any good? I have always heard that H is what you "set on the dial."
 

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