Law of Magnetism

The most basic law of magnetism is that like poles repel one another and unlike poles attract each other; this can easily be seen by attempting to place like poles of two magnets together.

Further magnetic effects also exist. If a bar magnet is cut into two pieces, the pieces become individual magnets with opposite poles. Additionally, hammering, heating or twisting of the magnets can demagnetize them, because such handling breaks down the linear arrangement of the molecules. A final law of magnetism refers to retention; a long bar magnet will retain its magnetism longer than a short bar magnet.

Carl Friedrich Gauss (1777-1855), Jean-Baptiste Biot (1774-1862), Felix Savart (1791-1841) and Michael Faraday (1791-1867) each created equations that explained what came to be known as the laws of magnetism. These were later expanded upon by James Clerk Maxwell (1831-1879) to become known as electromagnetism.

What happens inside materials when magnetised is explained by the domain theory of magnetism. All large magnets comprise smaller magnetic regions, or domains. The magnetic character of domains comes from the presence of even smaller units, called dipoles. Atoms are arranged in such a way in most materials that the magnetic orientation of one electron cancels out the orientation of another; however, ferromagnetic substances such as iron are different. The atomic makeup of these substances is such that smaller groups of atoms band together into areas called domains; in these, all the electrons have the same magnetic orientation.