Electromagnet
Purpose:
The operation of electromagnets is said about it: shove it into a coil a soft -
into it, the soft iron is magnetized, it transforms itself into a magnet. The field of this
Magnet is added to the coil, so that a total of a stronger field than the result without an iron core.
Deficiencies:
The statement suggests the expectation that the magnetization of iron is greater, the greater the
Permeability μ is. One would therefore expect that the electromagnet has so much stronger field, depending
larger μ. Now this is not the case. Thus, a coil for the electromagnet, it is sufficient that μ
large compared to 1. It makes virtually no difference whether μ equal to 1000 is 10 000 or even 100 000.
Origin:
The electromagnet is easily explained and directly, using the first Maxwell's equation, a
Statement about the magnetic field H makes. Now it has become established throughout magnetic fields
to describe the vector quantity B. This restriction to B is often justified by arguments
which have nothing to look at the physics: B is the real or fundamental field, H other hand, a
secondary or auxiliary variable. Here's a mistake is made, we do not our students to look elsewhere:
We confuse physical size and physical system. The sentence "In the spring depends on a mass"
is not correct, because a physical quantity can not depend on a spring. Likewise, neither
B nor H be the field for B and H are physical quantities, the magnetic field, however, is a physical
System.
The description of the effect of the iron core is now with the size of H is much simpler than with B. For
one can define very easily with H, what is meant by a soft magnetic material: Inside
of such a substance is H = 0 A / m, regardless of how the field is outside / 1 /. (This property is lost,
if the material gets into saturation. There is then no longer soft magnetic.) Second, one can
with H formulate a size that does not change upon insertion of iron core of its value, an invariant
So: the path integral over a path that winds around the current-carrying wires just once. If
Now a part of the path of integration, namely the interior of the iron core, the field H made null
is so, the contribution to the integral on the rest of the way, that is outside of the coil, according
. grow
If the declaration without the magnetic field strength, ie, trying only to the flux density, it has been
firstly, difficult to describe the properties of soft magnetic material, and secondly
one lacks the invariant in the process of pushing the iron core.
Disposal:
For the explanation of phenomena that are related to the magnetization of matter, use the
magnetic field H. If we take H as a measure of what one wants to be understood by a lot or a little box
we can formulate the fact that soft magnetic materials in the interior of H = 0, then: Soft magnetic
Substances can be no magnetic field to penetrate into themselves, - as well as electrical conductors, the
not let electric field in itself. Thus one can now easily understand even the electromagnet:
Moves to one soft-iron into a coil, while holding constant the electrical current, so
the iron core pushes out the magnetic field from the interior of the coil.
/ 1 / Herrmann, F.: Contaminated physics (4), The Hysteresiskurve
Legacy of physics (36)