Transcript document

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”
How good was this early theory? Import to life? Consider also II Peter 3:5.
 Intrigued by 2 mysterious phenomenon
►That
magnetite attracts iron
►That rubbed amber attracts a light dry object
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)
Why might he have been one of the first to notice this phenomenon?
► 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
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