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ELECTROMAGNETIC FORCE

An electromagnetic force is a force that acts on a conductor when current flows in the conductor within a magnetic field. It is utilised to operate starter and wiper motors, and the pointers of ammeters, voltmeters, etc.

DIRECTION OF ELECTROMAGNETIC FORCE

Let’s assume the N and S poles of a magnet are placed near other, and a conductor is put between them, as shown. Then current is applied to the conductor.


The following can be said about the magnetic flux created in this case: There are a smaller number of magnetic lines of force above the conductor since the direction of the magnetic fluxes created by the magnet and the direction of those created by current oppose each other. In contrast, there are a larger number of magnetic lines of force under the conductor as their directions coincide.
Since magnetic lines of force act similarly to stretched rubber bands in many ways, the magnetic lines of force attempt to become straight. This tendency is stronger under the conductor than above it. Therefore, a force is generated that tends to push the conductor upward. This force (F) is called an electromagnetic force.
The direction of an electromagnetic force can be determined from Fleming’s left-hand rule.

STRENGTH OF ELECTROMAGNETIC FORCE

Strength F of an electromagnetic force varies in proportion to density B of the magnetic flux (the number of magnetic lines of force per unit area), current flowing l in the conductor, and length L of the conductor, as expressed below:
F = B x I x L
In other words, an electromagnetic force is greater when there is a stronger magnetic field, when more current flows in the conductor, or when the length of the conductor within the magnetic field is greater.


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