An analysis of the magnetic pull force which arises between the poles of an electromagnet
Overview
Key facts
For an electromagnet characterized by the area , the magnetic flux density , and the relative magnetic permeability , the magnetic pull force is:
where is the magnetic permeability of free space.
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Constants
Consider an electromagnet of area and magnetic flux density , and also imagine a displacement of as highlighted in Figure 1.
Figure 1
We know that the energy stored in a magnetic field of no magnetic saturation is given by:
where is the volume, the magnetic permeability of free space, and the relative magnetic permeability (for a more detailed discussion on the energy stored in a magnetic field see Stored Energy ).
Thus, the change in energy stored following the displacement will be:
Consider the electromagnet diagramed in Figure E1, characterised by the lengths , , and , and the area . Given that a current of passes through a coil with turns and relative magnetic permeability of , find the total magnetic pull force.
Figure E1
Workings
We know that the total magnetic reluctance of a magnetic circuit of length , cross-sectional area , and relative magnetic permeability , with an air gap of length , is given by: