Download ph19510 lecture4

Chaos, Communication and
Consciousness
Module PH19510
Lecture 4
The Dawn of the Electric Age
Review of Lecture #2
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Pre-electronic Communication
 Pictographs
 Development
of the alphabet
 Number systems
 Printing
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Transfer of Information
 Navigation
 Signalling
Communication
The dawn of the electric age
The Electric Pioneers
 First messages by wire
 Development of telegraphy
 Samuel Morse and his code
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Highly Recommended
Electric Universe
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David Bodanis
£7.99
ISBN
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0-349-11766-7
Aventis prize for
popular science
How Electrons hold
the universe together
Electricity in antiquity
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Lightning
Ancient Greece
Thales (600BC)
Rubbed Amber with
fur  picked up
feathers
Static electricity
“Resinous” vs
“Vitreous”
Benjamin Franklin (1706-1790)
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Printer, scientist,
writer, inventor,
activist, statesman
Static electricity
+ve and –ve charge
1752 Proved storm
clouds are charged
Luigi Galvani (1737-1798)
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1780 Frogs leg
Dissimilar
metals
Static
Bioelectricity
Alessandro Volta (1745-1827)
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Lombary, Italy
1800
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Voltaic pile
 Battery
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Zinc/Silver
Brine/Cardboard
Steady current
The Zinc/Silver Cell
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Zinc Anode
Silver Cathode
Zn(s)  Zn2+(aq) + 2e2H+(aq)+2e-  H2 (g)
≈0.75 volts/element
+ve
Ag
Cardboard +
Brine
-ve
Zn
1820 – A key year
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Link between Electricity & Magnetism
 HC
Ørsted (Denmark)
 Compass needle
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Galvanometer
J
Schweigger
 Wind wire around compass
 Increased sensitivity
Andrè-Marie Ampere (1775-1836)
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1820 Formalised EM
Theory
1821 Proposed
Telegraphy with
galvanometers
1 wire per
galvanometer
200 ft (60-70m)
Early systems based on
galvanometers
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Schilling 1832
Gauss & Weber 1833
Wheatstone & Cooke
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5 Needle Telegraph
1837
Commercial system
1839
William Sturgeon invents the
Electromagnet 1825
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b. 1783
1825 Electromagnet
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Coil of wire on iron
 Uninsulated wire
Joseph Henry (1797-1878) –
Electrical signalling at a distance
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1827 Improves
electromagnet
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1830 First signalling
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Many turns of insulated wire
Ring bell >1 mile of cable
1837 Electromechanical
Relay
The electromechanical relay
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Switch held open by
spring
Electromagnet
Current flows in
electromagnet
 magnetic field
 switch actuated
Current flows in
switched circuit
Samuel Morse & Alfred Vail
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1838 – First system test
Vail developed signalling code
1843 – U.S. congress funds $30,000 for line
from Washington to Baltimore – 40 miles (65km)
1844 Line operational
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“What hath God wrought”
Morse’s apparatus
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Paper tape moved by
clockwork
Electromagnet pulls
‘pendulum’
Marks embossed on
paper tape
Paper Tape Output
Morse Code
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Evolved from Vail’s
original
Letters & Numbers
Punctuation
2 symbols
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Dot
Dash
Variable length
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Frequent letters, shortest
codes
Review of Lecture #3
Dawn of the electric age
 Key technologies
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 Cells
& Batteries
 Electromagnet
 Relay
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Use of standardised code