Field due to Magnetic Materials

[physiguy]

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

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!

 

[Meir Achuz]

The magnetization of the material affects both fields outside, but B and H are still equal.

 

[physiguy]

So let's say that I have a sphere (radius R) of permeability $\mu$ 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 $H=(1/\mu_0)B-M$?

 

[physiguy]

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."