A magnet is a substance that attracts pieces of iron, cobalt, nickel, etc and aligns itself in the north- south direction when suspended freely. The Greeks knew the phenomenon of magnetism, as early as around 800 BC. They discovered that certain stones, now called magnetite (Fe304), attract pieces of iron. The Chinese called it the Lodestone i e. the leading stone. In 1269 Pierre de Maricourt found that magnet has two poles, North Pole and South Pole. Subsequent experiments showed that every magnet, regardless of its shape, has two poles. In 1600 William Gilbert extended these experiments to a variety of materials. Using the fact that a compass needle orients in preferred directions, he suggested that the earth itself is a large permanent magnet. It was Oersted who in 1819 gave the first evidence of the connection between electricity and magnetism. The cause of magnetism is the motion of charges.
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A magstripe on a credit card contains millions of tiny magnetic domains held together by a resin.