Chaos, Communication and ConsciousnessModule PH19510

Lecture 4

The Dawn of the Electric Age

Review of Lecture #2

Pre-electronic Communication Pictographs Development of the alphabet Number systems Printing

Transfer of Information Navigation Signalling

CommunicationThe dawn of the electric age The Electric Pioneers First messages by wire Development of telegraphy Samuel Morse and his code

Highly RecommendedElectric Universe David Bodanis £7.99 ISBN

0-349-11766-7

Aventis prize for popular science

How Electrons hold the universe together

Electricity in antiquity

Lightning Ancient Greece Thales (600BC) Rubbed Amber with

fur picked up feathers

Static electricity “Resinous” vs

“Vitreous”

Benjamin Franklin (1706-1790)

Printer, scientist, writer, inventor, activist, statesman

Static electricity +ve and –ve charge 1752 Proved storm

clouds are charged

Luigi Galvani (1737-1798)

1780 Frogs leg Dissimilar

metals Static Bioelectricity

Alessandro Volta (1745-1827)

Lombary, Italy 1800

Voltaic pile Battery

Zinc/Silver Brine/Cardboard Steady current

The Zinc/Silver Cell

Zinc Anode Silver Cathode Zn(s) Zn2+(aq) + 2e-

2H+(aq)+2e- H2 (g)

≈0.75 volts/element

Ag

Zn

+ve

-ve

Cardboard + Brine

1820 – A key year

Link between Electricity & Magnetism HC Ørsted (Denmark) Compass needle

Galvanometer J Schweigger Wind wire around compass Increased sensitivity

Andrè-Marie Ampere (1775-1836)

1820 Formalised EM Theory

1821 Proposed Telegraphy with galvanometers

1 wire per galvanometer

200 ft (60-70m)

Early systems based on galvanometers Schilling 1832 Gauss & Weber 1833 Wheatstone & Cooke

5 Needle Telegraph 1837

Commercial system 1839

William Sturgeon invents the Electromagnet 1825 b. 1783 1825 Electromagnet

Coil of wire on iron Uninsulated wire

Joseph Henry (1797-1878) – Electrical signalling at a distance 1827 Improves

electromagnet Many turns of insulated wire

1830 First signalling Ring bell >1 mile of cable

1837 Electromechanical Relay

The electromechanical relay

Switch held open by spring

Electromagnet Current flows in

electromagnet magnetic field switch actuated Current flows in

switched circuit

Samuel Morse & Alfred Vail

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

“What hath God wrought”

Morse’s apparatus

Paper tape moved by clockwork

Electromagnet pulls ‘pendulum’

Marks embossed on paper tape

Paper Tape Output

Morse Code

Evolved from Vail’s original

Letters & Numbers Punctuation 2 symbols

Dot Dash

Variable length Frequent letters, shortest

codes

Review of Lecture #3

Dawn of the electric age Key technologies

Cells & Batteries Electromagnet Relay

Use of standardised code