Transcript Exploring Electrical Technology

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
► Lodestone:
also known as magnetite, is a
magnetic oxide of a common metal that has
magnetic properties
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)
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
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)
Origins:
Early Understanding of Magnetism
► Promoted
by Petrus Peregrinus de Mericourt
 Background and occupation:
 Published Epistola de magnete
 Concepts he contributed
►The
identity of magnetic poles…
►That magnetic poles remain distinct…
►The observation that unlike poles…
►That a strong magnet can _____ the polarity of a
weak one (try on a nail and sense with a compass)
Origins:
Early Understanding of Magnetism
► Christopher
Columbus:
discovered declination
► By
1550, Robert Norman (English) had
described the magnetic dip (inclination):
Summary
► Magnetism
and Electricity originally discovered as
________ phenomena with special powers
► Lodestone became the basis of a magnetic
compass to facilitate _________
► Peregrinus promoted understanding of _________
► Experienced navigators discovered two non-ideal
aspects of compass performance: