Magnetism

Magnetism, name for a force that occurs naturally in certain substances and can be transferred to or induced in others. The basic properties of magnetism are its complementary forces of attraction and repulsion and its capacity to align itself on a roughly north-south axis. These properties occur naturally in magnetite and, in the form of the lodestone, were observed and exploited to some degree in ancient times. The force of magnetism is dipolar, on a north-south axis, corresponding approximately to the north and south magnetic poles of the earth. In a magnet, unlike poles attract; like poles repel. And if it is divided, the parts of a magnet will also be dipolar. It was early discovered that magnetism not only attracts iron, but can be transferred to iron. Metals which can be readily magnetized are called ferromagnetic and, besides iron and steel, include nickel and cobalt. A magnet, then, is anything that has the properties of magnetism.

Magnetism also exhibits a field. The shape of a magnetic field and its lines of force can be seen by sprinkling iron filings over a sheet of paper placed on top of a magnet. In the 19th century, scientists made discoveries about the relationship between magnetism and electricity. It was found that the forces between magnetic dipoles are identical to those between electrical dipoles and that electric currents generate a magnetic field. Further research revealed that it is possible to generate an electric current in a conductor by changing the magnetic fields around it, a phenomenon known as electromagnetism. This interrelation between electrical charge and magnetic force is present in matter on the atomic level as well. And the earth itself has a magnetic field which scientists hypothesize is generated and maintained by large electric currents caused by movement in the planet's liquid core.