Electricity

1
Electricity

• You Light Up My Life!

2
What is Electricity?

• Electricity is one of the two long-range
  fundamental forces of nature the other one being
  gravity.
• Gravitational force between two bodies is
  always attractive and depends on mass (in kg).
  Electric force can be both attractive and
  repulsive and depends on charge (in Coulombs).
  In both cases the force falls with the square of
  the distance apart.
• There are two kinds of electric charge
  positive and negative. Like charges repel and
  unlike charges attract.
• Gravity is a very weak force electric forces
  are trillions of times stronger but most
  materials have the same number of positive and
  negative charges, which cancel out, and so do not
  have any electric activity.

3
Atomic Theory

• All matter in the universe is made up of around
  90 different elements with Hydrogen (H) being
  the lightest (and most common) and Uranium (U)
  the heaviest (there are artificial elements,
  mostly above U in the periodic table).

4
Atomic Theory

• If you keep subdividing an element down, you
  reach the smallest particle that has the chemical
  properties of the element. This particle is
  called an atom (greek átomos meaning
  indivisible).
• Atoms are incredibly small. For instance a you
  could fit around 70 million carbon atoms across
  one of your hairs (0.1mm). One atom weighs 0.000
  000 000 000 000 000 000 02gm (or around 20
  trillion trillion would weigh a gram)!

• Atoms are smaller than the wavelength of light
  and so cannot be seen even with the most powerful
  optical microscope. However, they can be
  visualised by bombarding with electrons. The
  picture to the right shows an array of carbon
  atoms taken with a scanning tunnelling electron
  microscope.

5
Atomic Structure

• The big question of the late Victorian era was
  could an atom be made up of even smaller
  components?
• In 1874, the Irish physicist Johnston Stoney at
  a British Association conference meeting in
  Belfast predicted that there was a basic particle
  of electric charge as a constituent of the atom.
  He called these electrons.
• In 1897 JJ Thompson applied a high voltage
  across electrodes (the positive called the anode
  and the negative the cathode) in a vacuum tube
  generated cathode rays, which seemed consist of
  negatively charged corpuscles. These had the
  predicted unit of charge.

JJ Thompson and one of his cathode ray tubes
6
Atomic Structure

• Further experiments by Earnest Rutherford at
  the University of Manchester showed that the atom
  comprised of a number of electrons together with
  the same number of positively charged protons.
  Each particle carried one of Stoneys fundamental
  charge measured as 1.6 ? 10-19 Coulombs.
  Rutherford predicted that there would also be
  neutral particles in the atom, and neutrons were
  discovered in 1932 by James Chadwick at
  Cambridge.
• A proton weighs in at around 1.6 ? 10-24 gm
  against the lightweight electron which is around
  9 ? 10-38 gm, or 1/1836 of a proton. A neutron
  is only slightly heavier than a proton.

Rutherford left and Chadwick on the right
7
Atomic Structure

• JJ Thompson thought that the atom consisted of
  a mixture of electrons and protons all mixed
  together the plum pudding model (the positive
  and negative charges holding everything
  together). Electrons moved in rings inside this
  blob.
• In 1909 Rutherford and Geiger shot alpha
  particles (negative Helium nuclei) from radium (a
  radioactive element) at very thin gold foil.
  Most went right through but a very few bounced
  back. From this he deduced that the atom was
  mostly empty space.
• If all the space was removed from the human
  population of 6 billion, then the solid remainder
  would be the size of an apple!

8
Atomic Structure Bohr model

• By 1913 Neils Bohr, a Danish physicist,
  developed a model of the atom, where the
  electrons rotated in rings at a great distance
  from the positive nucleus, giving an overall
  neutral atom
• Only certain orbits were allowed (like
  harmonics in a vibrating violin string) and only
  a maximum number of electrons could populate each
  orbit (inner 2, next out 8 etc). These electrons
  were stable, that is they wouldnt spiral into
  the positive nucleus.
• Electrons absorbing energy can make a quantum
  leap to a higher orbit, and conversely moving
  down causes radiation of energy as discrete
  frequencies of electro-magnetic waves (light,
  X-rays etc).

9
Atomic Structure Bohr model

• It is electrons in the outer orbit that
  interact with other elements, and thus give
  chemical properties. Thus elements in the same
  column in the periodic table have similar (not
  identical) properties e.g. Carbon, Germanium,
  Silicon all have four electrons in their outer
  orbit. This orbit can hold a maximum of eight,
  so tend to steal electrons from other atoms e.g.
  a molecule of Carbon Dioxide CO2 shares two
  electrons with two oxygen atoms back and forth.
• The Bohr model is far too simplistic, and by
  the 1920s quantum mechanics painted a much more
  complex and mystical picture of sub-atomic
  physics, but the Bohr model still explains most
  of the phenomena useful in engineering

10
The Discovery of Electricity

• The ancient Greek mathematician Thales wrote in
  around 600bce that rubbing amber (fossilised tree
  resin) with fur etc could cause attraction
  between the two or even cause a spark. The Greek
  for amber is electron.
• Study of magnetism goes back to the observation
  that certain naturally occurring stones attract
  iron.
• There is some evidence that electroplating was
  used in Mesopotamia around 300bce (the Bagdad
  battery).

Attracting feathers with amber
11
Two Thousand Years Later

• Around 1600, William Gilbert, a physician who
  lived in London at the time of Queen Elizabeth I
  and Shakespeare, studied magnetic phenomena and
  demonstrated that the Earth itself was a huge
  magnet. (Magnetism is really due to moving
  charges.)
• He also studied the attraction produced when
  materials were rubbed, and named it the
  "electric" attraction. This is static
  electricity, usually caused when some electrons
  are rubbed off a material into another. In the
  picture below the little girls hair has been
  charged up and the hairs repel.

12
Benjamin Franklin

• In 1752, Franklin proved that lightning and the
  spark from amber were one and the same thing.
  This story is a familiar one, in which Franklin
  fastened an iron spike to a silken kite, which he
  flew during a thunderstorm, while holding the end
  of the kite string by an iron key.When
  lightening flashed, a tiny spark jumped from the
  key to his wrist. The experiment proved
  Franklin's theory, but was extremely dangerous -
  he could easily have been killed.
• Franklin coined the terms positive and negative
  charge, battery and conductor still used today.

13
Galvani and Volta
In 1786, Luigi Galvani, an Italian professor of
medicine, found that when the leg of a dead frog
was touched by a metal knife, the leg twitched
violently. Galvani thought that the muscles of
the frog must contain electricity. By 1792,
another Italian scientist, Alessandro Volta,
disagreed he realized that the main factors in
Galvani's discovery were the two different metals
- the steel knife and the tin plate - upon which
the frog was lying. Volta showed that when
moisture comes between two different metals,
electricity is created. This led him to invent
the first electric battery, the voltaic pile,
which he made from thin sheets of copper and zinc
separated by moist pasteboard.
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Voltacontinued
In this way, a new kind of electricity was
discovered, electricity that flowed steadily like
a current of water instead of discharging itself
in a single spark or shock. Volta showed that
electricity could be made to travel from one
place to another by wire, thereby making an
important contribution to the science of
electricity. The unit of electrical potential,
the Volt, is named after him.
Alessandro Volta and one of his piles (batteries)
15
Andre Marie Ampere
Andre Marie Ampére, 1775 1836, a French
mathematician who devoted himself to the study of
electricity and magnetism, was the first to
explain the electro-dynamic theory. A permanent
memorial to Ampere is the use of his name for the
unit of electric current. http//www.corrosion-do
ctors.org/Biographies/AmperBio.htm
16
Ohm
Georg Simon Ohm, a German mathematician and
physicist, was a college teacher in Cologne when
in 1827 he published, "The Galvanic Circuit
Investigated Mathematically". His theories were
coldly received by German scientists, but his
research was recognized in Britain and he was
awarded the Copley Medal in 1841. His name has
been given to the unit of electrical
resistance. http//www.corrosion-doctors.org/Biogr
aphies/OhmBio.htm
Voltage Current x
ResistanceV IR
17
Michael Faraday
The credit for generating electric current on a
practical scale goes to the famous English
scientist, Michael Faraday (the unofficial patron
saint of Electrical engineering). Faraday was
greatly interested in the invention of the
electromagnet, but his brilliant mind took
earlier experiments still further. If electricity
could produce magnetism, why couldn't magnetism
produce electricity?
18
Faraday.continued
In 1831, Faraday found the solution. Electricity
could be produced through magnetism by motion. He
discovered that when a magnet was moved inside a
coil of copper wire, a tiny electric current
flows through the wire. Of course, by today's
standards, Faraday's electric generator was crude
(and provided only a small electric current), but
he had discovered the first method of generating
electricity by means of motion in a magnetic
field.
19
Faraday . continued
Faraday also realized that magnetic and electric
forces acting at a distance can be conceptualized
as a force field hence electric and magnetic
fields.
Left Magnetic field from a bar magnet
visualized using iron filings (miniature magnets
lining up in the force field). Right Electric
field showing direction of force (on a ve
charge) near a negative charge q.
20
Edison and Swan

• Nearly 40 years went by before a really
  practical DC (Direct Current) generator was built
  by inventor Thomas Edison.
• In 1878 Joseph Swan, a British
  chemist/electrician, invented the incandescent
  filament lamp and within twelve months Edison
  made a similar discovery in America.
• The aggregate capital now actually invested in
  electrical industries, principally electric
  lighting, (electric) railway and power
  distribution, is estimated by the same authority,
  as not less than 275,000,000. Quote from the
  National Electric Light Association in 1889!
  www.edisonian.com/p004b002.htm

21
Edison and Swancontinued

• Swan and Edison later set up a joint company to
  produce the first practical filament lamp. Prior
  to this, electric lighting had been very powerful
  (too powerful for households) but crude arc
  lamps.
• Edison used his DC generator to provide
  electricity to light his laboratory and later to
  illuminate the first New York street to be lit by
  electric lamps, in September 1882. Edison's
  successes were not without controversy, however -
  although he was convinced of the merits of DC for
  generating electricity, other scientists in
  Europe and America recognized that DC brought
  major disadvantages.

Left A lamp used at the historic 1879 New Years
Eve demonstration of the Edison Lighting System
in Menlo Park, New Jersey.
22
Nichola Tesla

• Power is the product of voltage and current (V ?
  I). High voltages in the home are dangerous!
  Thus Edison had to generate and distribute his dc
  power at lowish voltages (110V), but the cables
  had to carry large currents. Losses in the
  cables are proportional to current squared (I2R),
  but the problem with dc is that it is very
  difficult to change the voltage. With ac it is
  easy just use a transformer. However, motors at
  the time would only run on dc.
• Nichola Tesla, a Croatian engineer working for
  Edison, conceived the idea of 2- and 3-phase
  generation (in a dream) and on this basis
  patented a motor running alternating current.
  This removed the chief objection to ac, but
  Edison fought this tooth and nail. With
  Westinghouse, Tesla was instrumental in the
  design and implementation of the Niagara Falls
  hydroelectric scheme, which supplied New York,
  over 20 miles away, with electricity. This
  effectively won the battle of the currents.

23
Nichola Tesla continued
Left Tesla monument at Niagra Falls (Canadian
side), Queen Victoria Park, unveiled on July 9,
2006.  Tesla is standing atop an AC motor. Right
Tesla took out over 700 patents! http//www.teslas
ociety.com/
24
The Information Revolution

• The use of electricity is critically important in
  lighting, heating, and in mechanical
  actuators/motors.
• Equally important is the use of electrons to
  generate, transmit, store and reproduce
  information.
• Information is a measure of change and
  predictability. Consider the two statements
• Tomorrow the sun will rise and darkness will be
  banished.
• Tomorrow an extinct volcano will erupt in
  Belfast.
• Which one carries the most information?
• Because electrons are so light, changes (called
  signals) can be sent along a conductor or
  propagated in space using radio or light waves at
  speeds approaching that of light.

25
The Information Revolution

• Up to the early 1800s the fastest you could send
  information was on horse by land or sailing ship
  by sea. A horseman carrying a message had to
  transport around 500kg of animal over rocks,
  muddy ruts and fallen trees with plenty of food
  for the two mammals.
• With a reliable source of electricity, around
  1830 many experiments were made in sending
  currents along wires to deflect a needle at the
  far end (magnetic field).
• Wires were strung on poles along railway lines to
  signal oncoming trains and synchronise time
  (railway time). In UK by 1838 there was 20km (12
  miles) of line, by 1852 there were 6,000km (4,000
  miles).
• The British system (Wheatstone Cook) used
  multiple wires and five needles to point to each
  letter in turn!

26
The Information Revolution

• Reducing the number of wires and reliability of
  the telegraph was a priority, and the number of
  needles was steadily reduced and various codes
  were used to encode alphanumerics.
• Samuel Morse (portrait Painter) with Alfred Vail
  came up with a code, which relied on each letter
  being coded by a series of dots and dashes. The
  more common letters had a shorter code. .-.. .
  -.-. - .-. .. -.-. .. - -.-- E l e c t
  r i c i t yThese current pulses could
  be used to close a relay switch and thus
  regenerate the signal along the link, and at the
  receiver mark a paper tape or actuate a buzzer.
• In 1844 first government-funded demonstration
  between Baltimore and Washington (37 miles).
  Message sent What has God wrought?

27
The Information Revolution
It is difficult to imagine how strange the
telegraph must have seemed to our great, great
grandparents. People had only the vaguest idea
about the technology involved. One railway
passenger who left her umbrella on the train
asked at the station if it could be found. The
stationmaster said he'd try to use the telegraph
to arrange for its return and wired to the end of
the line to see if it had been found on the
train. Soon, he received a message back that it
had and would be sent back 'down the line'. When
he told the anxious passenger this good news, she
expressed amazement that items such as umbrellas
could be returned using the telegraph! Rather
than disappoint her, the station staff hooked the
returned umbrella over the telegraph wire - as if
it had literally come back 'down the
line'. http//www.connected-earth.com/Galleries/i
ndex.htm
28
The Information Revolution

• Key to building an international communications
  web was undersea cables first across rivers and
  then seas.
• Needs great strength and good insulation
  invention of gutta-percha (rubber) led in 1850 to
  first international submarine telegraph between
  Dover and Cap Gris Nez (France). Four private
  investors each put up 500. Failed after a few
  messages!
• The wonder of the Victorian age (equivalent to
  putting a man on the moon) was the transatlantic
  link. Can you think of any problems laying 1,852
  miles (2,980 km) of cable?
• In 1857 and 1858 the HMS Agamemnon and USS
  Niagara met in mid-Atlantic, spliced the cable
  and sailed back towards their respective
  continents. Queen Victoria sent President
  Buchanan a 98-word message. Took 17 hours!

Authenticated left-over pieces of transatlantic
cable sold
29
The Information Revolution

• In an attempt to increase the signalling rate
  some genius decided to use 2,000 volts and
• It would take 12 years (and an American civil
  war) and seven attempts before a working link was
  established, with an investment of the equivalent
  of billions of pounds.
• The final cable (all 5,000 tonnes) was laid by
  Brunels giant Great Eastern ship from Valentia
  (Dingle Bay) to Hearts Content in Newfoundland.
• Lord Kelvin had invented the mirror galvanometer
  (very sensitive) and this allows a transmission
  rate of up to 20 words per minute with low
  voltages!.
• In 1871 a cable was laid to Australia via
  Singapore.
• By 1902 with the completion of a line from
  British Columbia to New Zealand, telegraph cables
  now circumnavigate the globe.
• The first Telephone (speech) transatlantic cable
  was not laid until 1956!

30
The Information Revolution

31
The Information Revolution

1924
32
The Information Revolution

• The electric telegraph was a digital
  communications network people speak in tones.
• To send sounds down a wire, you need to
• Convert sounds to electric current vibrations
  (that is an analogue to the original air pressure
  variations).
• Transmit these currents to the desired receiver.
• Turn electrical current variations back to
  pressure waves (sounds)
• Many people working at transmitting tones down a
  telegraph wire around 1870s, in order to try and
  send more than one morse-code message at a time ?
  multiplexing.
• Also experiments in teaching deaf people to
  recognise sounds with vibrating membranes.
• Telephone-like instruments 1862 ? 1872, developed
  by Philipp Reis German physics instructor.

• http//atcaonline.com/phone/

33
The Information Revolution

• The invention of the first practical telephone is
  normally attributed to Alexander Graham Bell, a
  Scottish scientist (with a deaf wife) who was
  working in Canada. Patented in 1876. Also
  Edisons carbon microphone.
• Lord Kelvin exhibited Bell's telephone to the
  British Association for the Advancement of
  Science at Glasgow in September. He described it
  as "the greatest by far of all the marvels of the
  electric telegraph". 1877
• Bell demoed to Queen Vic in 1878, with a
  long-distance call to Southampton. What do you
  consider to be the major problem with distance
  connections?
• 1879 first public telephone exchange Eight
  subscribers.
• 1880 first London telephone directory in January
  covered three exchanges and 250 subscribers. By
  April, 7 London exchanges, 16 provincial
  exchanges and 350 subscribers ..
• The first operators were boys, who turned out to
  be impatient and rude when dealing with phone
  customers. Their rudeness made them extinct
  within only a few years, replaced by females who
  were, "calm and gracious

34
The Information Revolution

• Long-distance links require amplification active
  electronic devices.
• In 1904 Ambrose Fleming invents the thermonic
  diode.
• Followed by Lee DeForests triode amplification
  valve (tube) in 1906. A small voltage on a grid
  could control a large current flowing between a
  hot cathode and anode.
• This led to the electronic revolution, with radio
  (wireless), telephone repeaters, audio amplifiers
  and television etc.
• Telephone exchanges were automated during the
  20th century (In Donegal not until late 1980s)
  and the switching technology formed the
  technological basis for the comeback of digital
  networks, such as computers.

35
The Information Revolution

• Although all the theory was known by the end of
  the 2nd World war it took the invention of the
  transistor in 1948 by Bardeen, Brattain and
  Shockley at Bell Laboratories to make it all a
  practical reality. Transistors control electrons
  travelling through a solid, such as silicon.
  Such structures can be made down to a few hundred
  atoms in size (which is where we came in), no
  vacuum, no hot filament. Small size means high
  speed and low energy required to switch.
• Hundreds of millions of these tiny switches can
  be put on wafers of silicon to make up an
  integrated circuit. Imagine a Pentium with 50
  million hot, fragile and limited-life thermionic
  tubes!

36
Electromagnetism

• James Clerk Maxwell (1831 - 1879) developed the
  laws of electromagnetism in the form we know them
  today Maxwells Equations
• Maxwells Equations are to electromagnetism what
  Newtons Laws are to gravity

Note It was Maxwell who realized the light is
electromagnetic in nature
37
What is Electricity?
- "Electricity" means electric charge. Examples
CHARGES OF ELECTRICITY. COULOMBS OF ELECTRICITY.
- "Electricity" refers to the flowing motion of
electric charge. Examples CURRENT ELECTRICITY.
AMPERES OF ELECTRICITY. - "Electricity" means
electrical energy. Examples PRICE OF
ELECTRICITY. KILOWATT-HOURS OF ELECTRICITY. -
"Electricity" refers to the amount of imbalance
between quantities of electrons and protons.
Example STATIC ELECTRICITY. - "Electricity"
is a class of phenomena involving electric
charges. Examples BIOELECTRICITY,
PIEZOELECTRICITY, TRIBOELECTRICITY,
THERMOELECTRICITY, ATMOSPHERIC ELECTRICITY
...ETC.
38
Electricity?

• Electricity is all about electrons, which are the
  fundamental cause of electricity
• Static Electricity - involves electrons that are
  moved from one place to another, usually by
  rubbing or brushing
• Current Electricity - involves the flow of
  electrons in a conductor

39
Electric Charge

• Two kinds positive and negative (terms coined by
  Benjamin Franklin)
• When you rub a glass rod with silk, the charge
  that is left on the glass was called positive. If
  you rub a hard rubber rod with silk, the charge
  left on the rod was called negative.
• Like charges repel while unlike charges attract.

40
On the Move

• Electrons in the outer rings or shells of atoms
  are bound more loosely to the nucleus
• Such electrons tend to break free from the
  nucleus and wander around amongst other nearby
  atoms
• Such electrons are called free electrons

41
Current Conduction

• Such movement of these free electrons creates
  an electric current
• Materials with large numbers of free electrons
  are called electrical conductors. They conduct
  electrical current.
• Movement of the electrons physically from one
  place to another is slow. Transfer of the energy
  from one electron to another happens fast.

42
Conductors and Insulators

• In conductors, electric charges are free to move
  through the material. In insulators, they are
  not.
• In conductors
• The charge carriers are called free electrons
• Only negative charges are free to move
• When isolated atoms are combined to form a metal,
  outer electrons of the atoms do not remain
  attached to individual atoms but become free to
  move throughout the volume of the material

43
Other Types of Conductors

• Electrolytes
• Both negative and positive charges can move
• Semiconductors
• In-between conductors and insulators in their
  ability to conduct electricity
• Conductivity can be greatly enhanced by adding
  small amounts of other elements
• Requires quantum physics to truly understand how
  they work

44
Simple Circuits

• Dont let the name fool you
• Bottom line For electric current to flow, there
  has to be a complete pathway for ita complete
  circuit.

45
Closed and Open Circuits

• Closed Circuit - an unbroken path of
  conductors through which electric current flows
• Open Circuit - a circuit with a break in the
  conductive path, so no current flows

Now, lets play Know Your Electrical Symbols!
46
Know Your Symbols

• Battery or Power Supply
• Resistor
• Capacitor
• Switch
• Conductive Wire

47
Series Circuits

• An electrical circuit with only one path for
  the electrical current to follow

48
Parallel Circuits

• An electrical circuit that provides more than
  one path for the electrical current to follow.

49
Static Electricity
Who hasnt rubbed a balloon on their hair and
stuck it to the wall?

• Buildup of charge (static, not moving)
• in one place.
• Charge can be either positive or negative

50
Beware of Door Knobs That Bite
More apt to happen in dry weatherwhy?