lec22 - 22-1Physics IClass 22The Magnetic FieldRev....

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Unformatted text preview: 22-1Physics IClass 22The Magnetic FieldRev. 13-Aug-04 GB22-2Magnetism in Ancient TimesThe ancient Greeks knew that the mineralmagnetite, named for the Magnesia regionof Asia Minor, attracts small iron objectslike nails. Magnetite is also known aslodestone.Ancient Chinese discovered the compassin the year 271 AD (or CE).The Chinese compass seen at the left usesa piece of magnetite shaped like a spoon.The handle of the spoon points south.22-3Peter PeregrinusPeter Peregrinus(Pierre de Maricourt) wasa member of the army of the King of Sicilyand probably served as an engineer. In 1269he described everything known aboutlodestones and how to make instrumentsusing these magnets. He discovered theexistence of magnetic poles and was the firstto use the word "poles." (Latin polus.) Hedid experiments referring to how the northand south poles attract or repel.He also described how to make a perpetual motion machine usingmagnets. People are still trying this (unsuccessfully) today!22-4William GilbertWilliam Gilbert, 1544-1603Gilbert published De Magnete(On the Magnet)in 1600. This book became a standard referenceon electricity and magnetism in Europe. Gilbertwas the first to distinguish the electricforce(named for the Greek word for amber) from themagneticforce. Gilbert debunked many folkmyths about the curative properties of magnets.Based on his observations of the preferred directions of thin ironneedles near spherical lodestones, and the similarity of thisphenomenon to the tendency of compass needles to tilt withrespect to the horizontal plane as well as point north-south,Gilbert deduced that the earth itself must be a giant magnet.22-5...
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This note was uploaded on 12/15/2010 for the course PHYS 0001 taught by Professor Nayak during the Spring '10 term at Rensselaer Polytechnic Institute.

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lec22 - 22-1Physics IClass 22The Magnetic FieldRev....

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