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lec22 - Physics I Class 22 The Magnetic Field Rev 13-Aug-04...

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22-1 Physics I Class 22 The Magnetic Field Rev. 13-Aug-04 GB
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22-2 Magnetism in Ancient Times The ancient Greeks knew that the mineral magnetite , named for the Magnesia region of Asia Minor, attracts small iron objects like nails. Magnetite is also known as lodestone . Ancient Chinese discovered the compass in the year 271 AD (or CE). The Chinese compass seen at the left uses a piece of magnetite shaped like a spoon. The handle of the spoon points south.
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22-3 Peter Peregrinus Peter Peregrinus (Pierre de Maricourt) was a member of the army of the King of Sicily and probably served as an engineer. In 1269 he described everything known about lodestones and how to make instruments using these magnets. He discovered the existence of magnetic poles and was the first to use the word "poles." (Latin polus .) He did experiments referring to how the north and south poles attract or repel. He also described how to make a perpetual motion machine using magnets. People are still trying this (unsuccessfully) today!
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22-4 William Gilbert William Gilbert, 1544-1603 Gilbert published De Magnete (On the Magnet) in 1600. This book became a standard reference on electricity and magnetism in Europe. Gilbert was the first to distinguish the electric force (named for the Greek word for amber) from the magnetic force. Gilbert debunked many folk myths about the curative properties of magnets. Based on his observations of the preferred directions of thin iron needles near spherical lodestones, and the similarity of this phenomenon to the tendency of compass needles to tilt with respect to the horizontal plane as well as point north-south, Gilbert deduced that the earth itself must be a giant magnet.
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