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6 Magnet Station Magnetic property of iron A magnetized iron bar has its power concentrated at two ends, its poles; they are known as its north (N) and south (S) poles, because if the bar is hung by its middle from a string, its N end tends to point northwards and its S end southwards. The N end will repel the N end of another magnet, S will repel S, but N and S attract each other. The region where this is observed is loosely called a magnetic field. Either pole can also attract iron objects such as pins and paper clips. That is because under the influence of a nearby magnet, each pin or paper clip becomes itself a temporary magnet, with its poles arranged in a way appropriate to magnetic attraction. Fundamental nature of magnetism is not associated with iron magnets but with electric currents The magnetic force is basically a force between electric currents. Bend copper wires into circles with constant separation (figure below): --Two circular currents in the same direction attract each other. --Two circular currents in opposite directions repel each other. Replace each circle with a coil of 10, 100 or more turns, carrying the same current: the attraction or repulsion increase by an appropriate factor. In fact, each coil acts very much like a magnet with magnetic poles at each end (an "electromagnet"). Ampere guessed that each atom of iron contained a circulating current, turning it into a small magnet, and that in an iron magnet all these atomic magnets were lined up in the same direction, allowing their magnetic forces to add up. Magnetism is light Today electromagnetic fields (and other types of field as well) are a cornerstone of physics. Their basic equations, derived by Maxwell, suggested that they could undergo wave motion, spreading with the speed of light, and Maxwell correctly guessed that this actually was light and that light was in fact an electromagnetic wave. Heinrich Hertz in Germany, soon afterwards, produced such waves by electrical means, in the first laboratory demonstration of radio waves. Nowadays a wide variety of such waves is known, from radio (very long waves, relatively low frequency) to microwaves, infra-red, visible light, ultra-violet, x-rays and gamma rays (very short waves, extremely high frequency).