Re: magnetism question



muknot@xxxxxxxxx wrote:

Hi I have a question:

Say you have a flux distribution due to a magnet, then you place a
piece of iron beside the magnet and you get a new flux distribution.
The flux density in the iron will be greater than the flux density in
the surrounding air. Why is this? Is it because the magnetization of
the iron creates additional flux in it, thus leading to more flux
density, or is it because the flux from the magnet prefers to travel
through the iron (rather than the surrounding air), thus leading to a
greater flux density or do both these effects contribute to a greater
flux density in the iron? Also if the flux from the magnet prefers to
travel through the iron, what's the reason for this (just saying that
it has higher magnetic permeability isn't much of an explanation)?

Another question I have is if you place a piece of iron in a magnetic
field that saturates it, and then remove a bit of iron (create a pit),
from the surface of your sample, the flux will "leake" out of your
sample. I don't understand why this happens, why doesn't the flux just
continue to travel through the air (where the pit is) with the same
distrubiton it had in the iron  -- why does it have to take up a
greater volume in the air?

The magnetic flux density represents the magnetic field strength at a given location. The field strength is in turn the vector sum of the fields of all of the contributing point sources superpose in space. The magnetic field of a source is in turn due to motion of point charges wrt the frame of reference chosen. The field of a hard magnet is regarded as arising due to electron *spin*, which IMO is a form of motion, but in small closed loops rather than in a macroscopic electron current.

Richard Perry

.

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