Electromagnetic Principles

The connection between electricity and magnetism was made by Oersted, a Danish scientist, in 1820. He had frequently demonstrated the nonexistence of a connection between electricity and magnetism. His usual procedure was to place a current-carrying wire at right angles to, and directly over, a compass needle to show that there was no effect of one on the other. One occasion, at the end of his lecture, he placed the wire parallel to the compass needle and saw the needle move to one side. When he reversed the current in the wire, the needle, to his amazement, deviated in the opposite direction. Thus a great discovery concerning electromagnetism was made quite by accident. There is no actual knowledge as to why some materials have magnetic properties and others have not. The "electron theory" generally is accepted as the best explanation of magnetism. It is also known as the "domain theory." According to the theory, an electron moving in a fixed circular orbit around the proton creates a magnetic field with the north pole on one side of the orbit and a south pole on the other side. It is assumed that the orbiting electron carries a negative charge of electricity, which is the same as electrical current flowing through a conductor. Current flow, then, is from negative to positive. When a number of magnetized orbiting electrons exist in a material, they interact with each other and form "domains," or groups of atoms having the same magnetic polarity. However, these domains are scattered in random patterns throughout and the material is, in effect, demagnetized. Under the influence of a strong external magnetic field, domains become aligned and the total material is magnetized. The strength of its magnetic field depends on the number of domains that are aligned. In magnetic substances, the domains align themselves in parallel planes and in the same direction when placed in a magnetic field. This arrangement of the electron-created magnets produces a strong magnetic effect. If you stroke a piece of hardened steel with a magnet, the piece of steel itself will become a magnet. (Steel railroad tracks laid in a north-to-south direction become magnetized because they lie parallel to the magnetic lines of the earth.) Much stronger magnets and magnetic fields can be produced by electrical means. Placing a piece of steel in any strong magnetic field will cause it to become magnetized. A magnetized field surrounds any conductor carrying an electrical current. The discovery of that fact resulted in the development of much of our electrical equipment. The "field of force" is always at right angles to the conductor. Since the magnetic force is the only force known to attract a compass needle, it is obvious that a flow of electric current produces a magnetic field similar to that produced by a permanent magnet. Not only is the field of force at right angles to the conductor, but the field also forms concentric circles about the conductor. When the current in the conductor increases, the field of force is increased. Doubling the current will double the strength of the field of force.