Magnetic forces act upon magnetic objects or charged particles moving through a magnetic field. They are affected by the strength of the magnetic field, the total charge of a particle, and its speed and direction. Permanent magnets have their molecular structures aligned during formation so that they will attract certain types of metals. Magnetic forces are exploited when electricity is converted to mechanical rotation, and vice versa.
The medium through which these forces are transmitted is the magnetic field. A magnetic field is created with a permanent magnet or an electric current. Since an electric current is a stream of moving charge carriers, such as electrons, it can be analyzed by considering only one particle. Thus, a single electron moving through space will create a magnetic field.
One common application of magnetic forces is the refrigerator magnet, which is a permanent magnet. Permanent magnets are subjected to a strong magnetic field when they are manufactured. In this process, their internal crystalline structures are aligned such that they remain magnetized. A permanent magnet will attract ferromagnetic materials such as iron. Ferromagnetism is only one source of magnetic forces, but it is the one commonly associated with magnetism in everyday situations.
Permanent magnets also exert magnetic forces on other magnets. This is when the magnets’ poles become important. Unlike electric field lines, magnetic field lines always circle around and form a closed loop. In other words, magnets always have two distinct poles, conventionally called a north and south pole. The same poles of two different magnets will repel, while opposite poles will attract.
Another situation where magnetic forces will arise involves two neighboring electric currents traveling at right angles to each other. These currents will produce their own magnetic fields, but they will be in different orientations, leading to forces between the two currents. The more current there is, the stronger the forces will be.
The interaction between magnets and an electric current is the basis of both the electric generator and the electric motor. For a generator, mechanical motion produced by a power plant or engine spins a component with magnets on it. The changing magnetic field will induce an electric current in the other part of the generator. When the device is used as a motor, it is the electric current that is supplied. The same magnetic forces will produce a mechanical torque to spin the other side of the motor.