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Exploring Electrical Technology. Origins of Electricity & Magnetism (E & M). Origins of E & M. Before the time of Christ: those who became familiar with the mysterious repulsive and attractive forces of certain materials included Chinese Greeks
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Exploring Electrical Technology Origins of Electricity & Magnetism (E & M)
Origins of E & M • Before the time of Christ: those who became familiar with the mysterious repulsive and attractive forces of certain materials included • Chinese • Greeks • Lodestone: a magnetic oxide of iron (also known as magnetite) naturally available in the earth, for those who stumbled upon it See also: http://www.phy6.org/earthmag/lodeston.htm
Origins of E & M: Chinese • Chinese: probably 1st to use lodestone for navigation • According to Timetables of Science • Chinese Book of the devil valley master contains first known reference to lodestone’s alignment with Earth’s magnetic field; here the lodestone is called a “south-pointer” (310-301 BC) Consider the wisdom of this early choice by the Chinese, in contrast to the later idea of Europeans, given what you learned from your experiment today.
Origins of E & M:Chinese • According to Timetables of Science • In China, by 271 AD, the first form of a compass was probably used for finding south • Tseng Kung Liang’s Wu Ching tsung yao (a compendium of important military techniques) describes the magnetized iron “fish” that floats in water and can be used for finding south; about the same time Chinese began applying the compass for navigation, most likely using the iron “fish” (1084 AD)
Origins of E & M:Definition of some key terms • Magnetic field: invisible lines of force along which a magnetized needle aligns itself if allowed to move freely • Navigation: finding out how to go (plotting a course) to get where one is going (destination) • Compass: in the magnetic version, relies on a pivoted, magnetized needle and Earth’s magnetic field to provide a reference direction for navigation
Origins of E & M:Chinese • Timetables of Science also cites • Chinese scientist Shen Kuo’s Dream Pool essays that contain the first known reference to the use of a magnetic compass for navigation • Chu Yu’s Pingchow table talk that contains the first mention in Chinese literature of a compass used for seagoing navigation • What about the geography of China might have made Chinese especially interested in the southerly direction?
Origins of E & M:Chinese precede Europeans; Greeks amused • This brief history suggests that Chinese discovered and may have invented the magnetic compass before Europeans. • On the other hand, Greeks intermittently intrigued themselves by mysterious powers of “magical” materials, during early days
Origins of E & M: Greeks • Ancient Greeks noticed both • Static (electric) forces • Magnetic forces • Found lodestone • Mentioned in Greek texts by 800 BC • Claim two possible origins of the word “magnet” • The province of Magnesia where mined (Lucretius) • The shepherd Magnes, its discoverer (Pliny the Elder)
Origins of E & M: Greeks • By around 600 BC, engaging interest emerged among Greeks w/Thales of Miletus • Greek mathematician, astron. & philosopher • Gave an interpretation of matter (~ 575 BC): “water is the basis of all things” • Intrigued by 2 mysterious phenomenon • That magnetite attracts iron • That rubbed amber attracts a light dry object How good was this early theory? Import to life? Consider also II Peter 3:5. Consider the demonstration as an illustration.
Origins of E & M: Greeks • Greeks were on the trail, but not scientifically yet, nor for applications • Rather they remained a bit confused, amused and entertained at best
Origins of E & M: Compass • Probably 1st practical application of magnet • Apparently 1st invented by Chinese • Origin uncertain: China, Italy or Arabia • 1st known Western reference to magnetic compass (~1195 AD) • By Alexander Neckham (b. St. Albans, England 1157) • In De naturis rerum (on natural things) Since this work occurred well before the printing press, how accessible and well distributed do you think this work may have been? Why?
Origins: Early Understanding of Magnetism • Promoted by Petrus Peregrinus de Mericourt • A French crusader and engineer • Published Epistola de magnete(letter on the magnet) • Concepts he contributed • The identity of magnetic poles by Earth analogy • That magnetic poles remain distinct even after a magnet is crushed • The observation that unlike poles attract • That a strong magnet can reverse the polarity of a weak one (try on a nail and sense with a compass)
Origins: Early Understanding of Magnetism • Christopher Columbus: while 1st voyaging to the Americas in 1492, found magnetic compass changes somewhat the direction it points as longitude changes (declination) • By 1550, Robert Norman (English) had described the magnetic dip (inclination): the increased angle of magnetic field lines with respect to horizontal near the poles Why might he have been one of the first to notice this phenomenon?
Summary • Magnetism and Electricity originally discovered as separate phenomena with special powers • Lodestone became the basis of a magnetic compass to facilitate navigation • Peregrenus promoted understanding of magnetism • Experienced navigators discovered non-ideal aspects of compass performance • Declination • Inclination