Electricity

1
Electricityprior to 18th-century people
experienced static electricity and naturally
occurring electricity (lightening) but didnt
understand it.
In 1663 a device similar to the Van de Graph
generator seen in lab was created.
2
Magnetismwas used in the 12th century when it
was discovered that an iron-rich magnetic
material would align itself with Polaris (the
north star). This mineral, magnetite, was the
first compass.
3

• The Chinese used a compass around 200 B.C to
  align buildings for best harmony.
• The Chinese are considered the first people to
  use the compass for navigation in the East and
  the Venetians were the first to use it in the
  West.

http//www.grand-illusions.com/compass.htm
www.aaei.org
4
Electricity

• Non-static electricity is the movement of
  negatively charged particles
• Electrons are negatively charged particles
• Unlike charges attract, like charges repel

5

• Electrons orbiting an atoms nucleus

http//earthsci.org/education/teacher/basicgeol/mi
ner/miner.html
Metals have lots of extra electrons roaming
about, so metals are good conductors of
electricity.
6
Electrons want to jump in holes

• Electrons orbit the nucleus of atoms
• Each electron has a charge of -1

• Holes are where electrons are needed to fill
  electron shells

7
What is a electrical conductor?

• A material that allows electrons to flow freely.
  Most metals are good electrical conductors.
  Outer electrons are loosely bound to the metal
  atoms, therefore they can roam freely.
• A material that strongly resists the flow of
  electrons is an insulator. Most non-metals are
  good insulators.

8
Static Charge

• When a bunch of negative particles are separated
  from positive particles (holes), an electrostatic
  force is created.

http//www.tpub.com/neets/book10/39i.htm
9
Electrical forces are much greater than
gravitational forces. Gravity is always an
attractive force, but electrical forces can be
both attractive or repulsive.
http//www.glenbrook.k12.il.us/gbssci/phys/Class/e
statics/u8l3b.html
10
Electrostatic forces can be stronger than the
force of gravity.
www.wfu.edu/physics
11
Xerographic Copies use electrostatic charge to
produce transfer images

• Photoconductor only conducts charge when exposed
  to light.
• A document image is projected onto a rotating
  photoconductor drum. An image identical to the
  original black and white is produced with charged
  particles. The portions that remain charged are
  the black.
• Oppositely charged toner adheres to the charged
  portion of the photoconductor.
• A charged piece of paper makes contact with the
  photoconductor and the toner image is transferred
  to the paper.
• The paper is then heated and the toner is fused
  onto the paper.

http//www.sciam.com/article.cfm?idhow-does-a-pho
tocopier-wo
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Chester Carlson Physicist, Engineer, Patent
Lawyer

• Develops the electrophotography process in 1938
• Acquires patents for the process
• Seeks investors from IBM, RCA, General Electric,
  and the US Army
• Finally in 1944 convinces Haloid Co. that idea
  has commercial viability.
• Process is coined XeroX, and Haloid Co. changes
  its name to Xerox and begins selling copiers in
  1950
• Plain Paper copies come out in 1959 sales surge
  along with Xeroxs revenue

13
Photocopier Process

• http//www.howstuffworks.com/photocopier1.htm

Photocopier Drums are light sensitive. They are
made of semiconductor materials. This
photoconductive material becomes conductive when
in light, but not conductive in the dark. Charge
can leave the drum where light hits the drum.
Charge remains in the areas where light did not
shine.
http//www.howstuffworks.com/photocopier1.htm
14
Leyden Jar

• In 1746 two scientists in Holland experimented
  with a device that could store charge/electrons.
  This was the first capacitor.

By touching the knob with a charged rod, more and
more charge could be stored in the Leyden Jar.
Homemade jar with tin foil. http//www.alaska.net
Wikipedia
15
Ben Franklins Kite Experiment

• Ben Franklin thought the sparks from static
  electricity looked a lot like lightning.

A wire was attached to the kites string with a
key at the end. The key was attached to a Leyden
Jar via a Small wire. It is unlikely Franklin
ever did the legendary experiment because two
people who tried this experiment died.
The installation of Lightening Rods to protect
tall buildings came from Franklin.
16
Van De Graph Generator produces static charge
17
Franklins Static Electric Motor

• Electrons hitch-hike on the thimbles to
  neutralize the side, thus making the rotor spin
  around.

http//f3wm.free.fr/sciences/jefimenko.html
18
What is electric current?I charge/time
The Physics Classroom

• Negatively charged particles called electrons
  are moving through conductors such as wires.
• If the electrons flow at a constant rate and
  always flow in the same direction, we say it is
  DC (direct current).
• If the electrons periodically change direction,
  the current is AC (alternating current).

19
Ohms Law

• V IR
• V voltage is electrical force that causes
  electrons to flow
• I - Current is the flow rate of electrons
• R Resistance to electron flow

20
Henry Cavendish (recall he discovered the
constant G)

• In 1781 Cavendish discovers electrical potential
  across a wire with resistance. He discovers that
  electric current naturally flows from high to low
  potential and the higher the potential the more
  current flows.
• Georg Ohm publishes the same result plus a
  complete theory on electricity in 1827.

V IR
21
Current in the Nichrome wire
Electrical Energy is converted into light and
heat by passing current through a resistive wire.
22
Power
Recall James Joule from the famous paddle wheel
experiment in the Thermodynamics section.

• P V I (watts Joules/sec)
• P Power is the rate of work being done
• (units are watts, horsepower, etc.)
• V Voltage (volts)
• I Current (amps)
• P X time Energy (KWH, BTU, Joules, Calories)

23
To perform work, a continuous flow of charge is
required

• Charge is expressed in Coulombs
• Current ? Coulombs/second
• Amp 1 Coulomb/second

Some kind of device or system was needed to
produce a continuous flow of charge.
24
Luigi Galvanis conducts experiments with animal
electricity using frogs legs
Meanwhile.

• Applying static electricity to dissected frogs
  legs caused the legs to twitch. (c. 1780)
• Galvani later laid frog legs out on brass hooks
  that were hooked onto an iron lattice during a
  thunderstorm. The frog legs continued to twitch
  after the storm.
• Alessandro Volta hypothesized that the twitching
  might be electricity caused by the two different
  metals (brass and iron).

25
Galvani hanging frog legs on brass
hooks. www.hgs.k12.va.us
Two metals causing legs To twitch. www.karisteeves
.net
Luigi Galvani http//itp.nyu.edu
26
Alessandro Volta and the Battery
A battery using copper and zinc, interleaved with
cardboard soaked in brine (a good electrical
conductor). Volta presented in 1800 the worlds
first device that could deliver continuous
current.

Wikipedia
An accomplishment that took 50 years, lots of
experimentation, and luck too.
http//ieee-virtual-museum.org
27

• An electrochemical cell has three main parts
  two dissimilar metals and an electrolyte. The
  electrolyte allows ions and electrons to move
  between the two metals. By creating a closed
  path, electrons will flow and electricity can be
  delivered to a device.

http//sxxz.blogspot.com
28
The Carbon and Zinc dry-cell battery

• First demonstrated in 1866.
• This is a chemical reaction where electrons are
  exchanged between two metals, causing continuous
  current through a load. This is a form of
  chemical energy.

Wikipedia
29
Battery Reactions

• Sulfuric Acid reacts with Zinc, producing
  positive zinc ions and electrons.
• Attaching a load (motor, light bulb, etc.)
  between the zinc and the graphite (carbon) allows
  the electrons to flow to the carbon side where
  the electrons join with H ions.

http//en.wikipedia.org/wiki/Zinc-carbon_battery
30
Lead Acid Battery Reactions

• Pb SO4² ? PbSO4 2e- HThe reduction
  potential of this reaction is 0.356 Volts.
• PbO2 SO4² 4 H 2e- ? PbSO4 H2OThe
  potential of this reaction is 1.685 volts.
• Total voltage created is about 2V.
• Lead Acid batteries provide high current,
• and are rechargeable, making them
• effective for starting cars.

http//sxxz.blogspot.com/2005/03/how-do-batteries-
work.html
31
An auspicious moment in 1820

• Hans Christian Oersted, a Danish Physics
  professor, was demonstrating electricity when he
  noticed that whenever the battery was connected
  such that current flowed in a wire, a nearby
  compass needle would twitch!!!
• Oersted by accident discovered that electricity
  and magnetism are related.
• His experiment showed that current in a wire has
  a magnetic field around it.

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http//www.gcse.com
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(No Transcript)
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Electromagnets in Industrial Applications
istockphoto
http//www.storchmagnetics.com
35
Michael Faraday

• Faraday was a self-taught scientist fascinated
  with science.
• In 1831 he showed the reverse of Oersteds
  experiment That electricity is created in a
  wire when the wire is moved through a magnetic
  field. This is called
• Electromagnetic Induction

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www.physics.uiowa.edu
37
Faradays Generator

• Faraday demonstrated that rotational energy
  could be converted into electrical energy.
• This was the first generator.
• It delivered continuous
• current.

http//www.powerstandards.com
38
Faraday demonstrates the Transformer

• Two coils very close together.
• Current in the first coil, sets up a magnetic
  field. This magnetic field induces current in
  the second coil.
• The transformer allows the stepping up or down
  of current based on the ratio of windings in the
  first coil to the second coil.
• If current goes up, voltage steps down. If
  current steps down, voltage steps up.

Wikipedia
39
Steam Powered Generators

• By the 1850s coal was burned to make steam
  which in turn was used to turn a generator to
  produce continuous current.
• Electricity meant instant, on demand clean power
  (never mind the coal burning in the next
  building).

40
http//sol.sci.uop.edu
41
Thomas Edison was determined to provide
electricity to light homes.

• Edison was convinced that electricity should be
  DC (direct current).
• DC voltage can not be easily stepped up to high
  voltages/low current, therefore it was
  impractical for supplying electricity over long
  distances.

42
DC makes an attempt

• In the 1880s there were a few DC power stations
  in England

43
Nikola Tesla invented the Generator/Dynamo in
1880s
Current alternates
http//www.physchem.co.za
44
AC wins by the 1890s

• AC power stations that generate power at 10,000
  volts are built. The voltage is stepped down
  using transformers.
• This is similar to todays technology.

http//www.energymanagertraining.com
Oregon Historical Society
45
Power Grid is based on AC voltageThis allows
stepping up and stepping down of voltage using
transformers.
http//www.windows.ucar.edu
46
Maxwells Equations

• James Clerk Maxwell took Faradays discoveries
  and put them into equations. The four equations
  state
• 1. Like charges repel, unlike charges attract
• 2. Magnetic fields always have two poles
  (positive and
• negative)
• 3. A moving/changing magnetic field can produce
  current.
• 4. Moving electrical charge (current) can
  produce a
• magnetic field.

47
From the Generator we get the Motor
The current direction in the wires changes with
every half rotation. This electromagnetic has a
constantly changing magnetic field, causing the
coil to continue to realign inside with the
permanent magnet (the stator). This makes the
rotor spin.
Wikipedia
48
Maxwell predicts Electromagnetic Radiation
An electromagnetic wave exists when the changing
magnetic field causes an electric field which
then causes another changing magnetic field, and
so on forever. These oscillating fields
together form an electromagnetic wave. An
electromagnetic wave will travel and continue on
forever until absorbed.
Wikipedia.com
49
Heinrich Hertz demonstrates in 1888 the existence
of electromagnetic radiation
50
Physical Contact does not need to be made to
measure electric or magnetic fields. An electric
field exerts a force on charged objects. A
magnetic field exerts a force on moving
charge. All the magnetic fields we experience
are the result of moving charges. Electromagnets
make magnetic fields with current in wires.
Permanent magnets produce magnetic fields through
the orientation of the electron orbits and spins
of the atoms in the magnet. Arthur Smith
51
Magnets
Since paired electrons spin in opposite
directions, their magnetic fields cancel one
another out. Atoms of ferromagnetic elements, on
the other hand, have several unpaired electrons
that have the same spin. Iron, for example, has
four unpaired electrons with the same spin.
Because they have no opposing fields to cancel
their effects, these electrons have an orbital
magnetic moment. Iron and other ferromagnetic
materials are crystalline. As they cool from a
molten state, groups of atoms with parallel
orbital spin line up within the crystal
structure, forming a permanent magnet. Magnets
attract materials that have unpaired electrons.
Howstuffworks
52
A non-turbine Generator(Micro Wind Generator)
http//link.brightcove.com/services/player/bcpid12
14137061?bctid1233395616
And where did this idea come from?
http//www.youtube.com/watch?vASd0t3n8Bnc
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Text Sources

• The Sciences- 5e, Trefil and Hazen
• A History of Great Inventions, James Dyson
• Internet