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Electric Motors

An electric motor is the reverse of a generator. A current flowing through a coil makes it behave as though it were a magnet with its own north and south poles. These poles attract or repel the poles of fixed ordinary magnets (unlike poles attract, like poles repel) and the combination of these forces rotates the coil. The rotation of the coil will continue indefinitely providing the direction of the current is changed twice every rotation-in fact, whenever the plane of the coil is at right angles to the magnetic field. The device which automatically changes the direction of current flow is called a commutator. A practical motor has a number of coils.

Direct current electric motors are constructed in the same way as dynamos. When they are switched on the electric current flows through the wires around the armature setting up a magnetic field around them. This field interacts with the main field of the rotor causing the wires on one side to be forced down and those on the other side to be forced up. This causes the armature to rotate and drive anything connected to the motor. Alternating current motors are constructed in a slightly different way, but work on the same principle.