Re: Question about magnetic forces beyond saturation


Salmon Egg wrote:
In article
<d52c8580-26ca-4fa1-b99a-59e938e878c8@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Jessie <jessie.taylor91@xxxxxxxxxxxxxx> wrote:

Hi,

We did not cover magnetism in depth in my Year 12 Physics syllabus,
particularly what happens beyond saturation. Googling around didn't
turn up much but perhaps I am searching for the wrong terms.

Based on my understanding of gravity and electrostatics, if we
increase the field strength of one test mass or charge, the force on
the other test mass or charge increases proportionally; i.e. the
amount of gravitational or electrical potential energy we get from
moving the test mass or charge from infinity to a specified distance
doubles if we double the fixed mass or charge.

If we place a ferromagnetic material in a field sufficiently strong to
just saturate it (say 2 Teslas), and measure the force acting on it to
be F...will this force increase to 2F if the field strength it is in
is increased beyond its saturation point to say 4 Teslas?

What are the typical pull forces of modern short duty resistive and
superconducting electromagnets 1m, 2m, etc away from them?

Do not try to use any understanding of gravity to understand magnetics.
For what you are asking. that is a dead end.

Look up magnetic circuits in a book that covers electrical machinery
such as motors and transformers. That uses saturable ferromagnetic
material.

There are two fields to consider, B and H. In terms of an electric
analogy, H is like an E field applied to a material. The response to the
H field is a B field. The electric analogy is that the displacement D is
the response to the E field.

Does that mean the B-field for a paramagnetic material will be small,
while diamagnetic materials will have negative B-fields?

Are magnetic forces inherently difficult to calculate because even for
a simple case of a ferromagnetic bar in a field produced by a bar
magnet, you are effectively looking at the superposition of four
monopoles as well as non-linear magnetisation of the ferromagnetic
material?

When saturation happens, there is no longer a big response to small
changes in H when applied to the material.

B is what what is measured in teslas. The driving magnetic field is
measured in amperes/meter. These are related by CHANGE in B equals mu
times the CHANGE in H. For a magnetic material, mu os large before
saturation and gets greatly reduced as saturation begins and beyond.

Bill

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