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| Jessie... |
 Posted: Fri Sep 25, 2009 4:41 am |
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Guest
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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?
Thanks.
Jessie xx |
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| Rich L.... |
| Posted: Sun Sep 27, 2009 9:03 am |
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Guest
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On Sep 25, 9:41 am, Jessie <jessie.taylo... at (no spam) googlemail.com> wrote:
[quote:987737f348]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?
Thanks.
Jessie xx
[/quote:987737f348]
Jessie,
The ferro magnetic material polarizes (becomes magnetized) as a result
of the H field applied to it by the external magnetic field (e.g. the
H field generated by the current in the coil surrounding the iron).
The forces on the ferromagnetic material are the result of the
interaction of the external magnetic field and the magnetic field of
the iron. Beyond saturation, the polarization of the iron does not
increase any more, so the forces will increase proportional to the
applied magnetic field only. Note that this is very different from
the case for fields weaker than the saturating field. In that case,
because the polarization of the iron increases with applied field, the
forces increase with the square of the applied field.
Note also that the forces on a polarizable material (this applies to
both magnetostatics and electrostatics) is very complicated and
depends not just on the strength of the field but also on the gradient
of the fields where the dielectric/ferromagnetic material is located
and also on the shape of the material. A spherical material in a
uniform field will experience no forces at all. Rod shaped material
in a uniform field will experience torques that (for normal
dielectrics and para/ferro magnetic materials) will tend to align them
to the external fields.
Rich L. |
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