The major magnetic field on planet Earth is the one which comprises the North Pole and the South Pole. By hanging a piece of magnetite, a rock with the properties of a magnet, from a string, the rock turns until it points north and south, towards Earth's poles. Based on this fact, both compasses and magnets were created, as well as electromagnets. All compasses and magnets contain, by default, a north pole and a south pole, like magnetite, and like the Earth itself.
Since all magnets, and electromagnets, have poles, it should be remembered that like poles, such as two north poles, repel each other, and unlike poles, such as one north pole and one south pole, attract each other. This is due to something called lines of force. Atoms in a magnet do not cluster, as in other metal objects, but form straight lines, which create poles through the resultant lines of force. The lines of force in any magnet, including electromagnets, radiate from each end of the magnet, and curve outward from the ends, as the lines of force reach for the other end of the magnet, or the opposite pole. The area surrounding the magnet, or electromagnet, which contains this curving line of force radiation, is called the field of force, or a magnetic field. An electromagnet generates an electromagnetic field.
An electromagnet is created by winding insulated copper electrical wiring around a piece of conductive metal, such as soft iron. When electric current passes through the wiring, the soft iron becomes and remains magnetized, as long as the current passes through the wire. This is the basis of the electric motor. Since electricity is created by passing unattached electrons, which are seeking positive charges to which they can attach, along a wire, bombarding the atoms of the soft iron with the negative pulse of the electrons, it temporarily creates lines of force within the soft iron, creating a magnet, or electromagnet.
Electricity can be generated using either direct or alternating current, the form most commonly used. A direct current flows continuously in one direction, while alternating current changes direction. Alternating current change intervals occur with a frequency of cycles per second. When the current changes directions, the poles in the electromagnet change positions. This occurs many times per second. If a magnetic compass were placed near an electromagnetic coil using alternating current, its needle would gradually lose its magnetism, due to being jerked back and forth by the polar changes of the alternating current. In contrast to the natural object of the compass, the electromagnet continues to operate as a magnet, until the moment at which the flow of electricity is stopped. The center of the electromagnet, such as soft iron, then resumes its natural state.
There are two principles of electromagnetism:
1. Electricity in motion produces a magnetic field.
2. A magnetic field in motion across an electrical field produces an electromotive force.
The first principle has been previously discussed. To illustrate the second principle, it is possible to pass the magnetic force generated by one electromagnetic coil to an adjacent coil. This is called electromotive force. The second coil will exhibit the same alternating current polar changes as the first coil, creating the same magnetic field as the first coil.
Principles aside, it is fascinating that electromagnets, electromagnetism, and electromagnetic fields all owe their existence to a little piece of magnetite.