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 mysterious repulsive and attractive forces of certain materials included 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:

Origins of E & M: Chinese ► Chinese: probably 1 st to use lodestone for navigation 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” ( 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 1 st practical application of magnet ► Apparently 1 st invented by Chinese ► Origin uncertain: China, Italy or Arabia ► 1 st 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