Transcript Slide 1

Electricity…
prior to 18th-century people
experienced static electricity and
naturally occurring electricity
(lightening) but didn’t understand it.
In 1663 a device similar to the Van de Graph
generator seen in lab was created.
Magnetism…
was 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.
► The
Chinese used a
compass around 200 B.C to
align buildings for best
harmony.
http://www.grand-illusions.com/compass.htm
► 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.
www.aaei.org
Electricity
► Non-static
electricity is the movement of
negatively charged particles
► Electrons are negatively charged particles
► Unlike charges attract, like charges repel
Electrons orbiting an
atom’s nucleus:
http://earthsci.org/education/teacher/basicgeol/miner/miner.html
Metals have lots of extra electrons roaming about,
so metals are good conductors of electricity.
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
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.
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
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/estatics/u8l3b.html
Electrostatic forces can be stronger
than the force of gravity.
www.wfu.edu/physics
Xerographic Copies use electrostatic
charge to produce & transfer images
►
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►
►
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?id=how-does-a-photocopier-wo
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 Xerox’s revenue
Photocopier Process
http://www.howstuffworks.com/photocopier
1.htm
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.
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
Ben Franklin’s Kite Experiment
Ben Franklin thought the sparks from static
electricity looked a lot like lightning.
A wire was attached to the kite’s
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.
Van De Graph Generator produces
static charge
Franklin’s 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
What is electric
current?
I = charge/time
Negatively charged particles called electrons are moving
through conductors such as wires.
The Physics
Classroom
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).
Ohm’s 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
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.
Ohm publishes the same
result plus a complete theory on
electricity in 1827.
Current
Voltage
► Georg
V = IR
Current in the Nichrome wire
Electrical Energy is converted into light and heat
by passing current through a resistive wire.
Power
P = V I (watts = Joules/sec)
Recall James Joule from
the famous paddle wheel
experiment in the
Thermodynamics section.
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)
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.
Meanwhile….
Luigi Galvani’s conducts experiments
with “animal electricity”
using frogs’ legs
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).
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
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 world’s 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
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.
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
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
Lead Acid Battery Reactions
Pb + SO4²¯ → PbSO4 + 2e- + H+
The reduction potential of this reaction is +0.356 Volts.
PbO2 + SO4²¯ + 4 H+ + 2e- → PbSO4 + H2O
The 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
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.
Current in wire
Compass
http://www.gcse.com
Electromagnets in Industrial Applications
istockphoto
http://www.storchmagnetics.com
Michael Faraday
Faraday was a self-taught scientist
fascinated with science.
In 1831 he showed the reverse of Oersted’s
experiment: That electricity is created in a
wire when the wire is moved through a
magnetic field. This is called
Electromagnetic Induction
www.physics.uiowa.edu
Faraday’s 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
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
Steam Powered Generators
By the 1850’s 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).
http://sol.sci.uop.edu
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.
DC makes an attempt…
In the 1880’s there were a few DC power
stations in England
Nikola Tesla invented the
Generator/Dynamo in 1880’s
Current alternates
http://www.physchem.co.za
AC wins by the 1890’s
AC power stations that
generate power at 10,000 volts
are built. The voltage is
stepped down using
transformers.
This is similar to today’s
technology.
Oregon Historical Society
http://www.energymanagertraining.com
Power Grid is based on AC voltage
This allows stepping up and stepping
down of voltage using transformers.
http://www.windows.ucar.edu
Maxwell’s Equations
James Clerk Maxwell took Faraday’s 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.
From the Generator we get the Motor
The current direction in the wires changes with every half Wikipedia
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.
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
Heinrich Hertz demonstrates
in 1888 the existence of
electromagnetic radiation
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
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
A non-turbine Generator
(Micro Wind Generator)
http://link.brightcove.com/services/player/bcpid1214137061?bctid=1233395616
And where did this idea come from?
http://www.youtube.com/watch?v=ASd0t3n8Bnc
Text Sources
► The
Sciences- 5e, Trefil and Hazen
► A History of Great Inventions, James Dyson
► Internet