Transcript magnetic field. - labsanywhere.net

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Lodestones
Bar magnet
Audio tape and magnet
Iron shavings in Lucite
Old CRT
Coil, power supply, & compass
Motor
Paint stick, magnet, and electromagnet
DC Ammeter, coil, magnet
Two coils, DC Ammeter, power supply
relay
Buzzer
Transformer
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
An auspicious moment in 1820…
Hans Christian Oersted, a Danish Physics
professor, was demonstrating electricity when he
noticed that whenever his battery was connected
to a loop of wire, a nearby compass needle would
twitch!!!
His experiment showed that current in a wire has
a magnetic field around it.
Oersted discovered that electricity produces a
magnetic field.
http://www.gcse.com
Oersted discovered that electricity produces a magnetic field.
Electromagnets in Industrial Applications
istockphoto
http://www.storchmagnetics.com
► Static
electric charge
produces an electric
field.
► Moving
electric charge
produces a magnetic
field.
All magnetism arises from moving charge
A Permanent Magnet is made from a
material that has many atoms that act like
tiny bar magnets, where all the atomic
magnets are lined up producing bulk
magnetism.
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Permanent Magnet
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Magnets
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 line up within the crystal structure,
forming a permanent magnet.
Magnets attract materials that have unpaired
electrons.
Howstuffworks
Electromagnets used in Tape Players
The electromagnet
consists of an iron core
wrapped with wire, as
shown in the figure.
During recording, the
audio signal is sent
through the coil of wire
to create a magnetic
field.
A – Tape
HowStuffWorks
This field magnetizes the
magnetic oxide on the
tape.
Sea floor as a magnetic tape
Earth’s outer core is
liquid. The earth’s
magnetic field
reverses itself
periodically. The
rocks at oceanic
spreading centers
have atomic magnets
that are aligned with
what the earth’s
polarity was at the
time the rock
solidified.
CRT coils “steers” electron beam
The motor is a
rotating loop of
wire with current in
it that spins in the
presence of a
magnetic field.
The Commutator
has two rotating
contacts with a gap
in the middle.
The brushes allow
the contacts to
slide while still
making electrical
contact.
The current
changes direction
every 180o
The Motor
The Speaker
Michael Faraday
Faraday was a self-taught scientist.
In 1831 he showed that electricity is
created from a changing magnetic
field.
Electromagnetic Induction
www.physics.uiowa.edu
The Generator
This generator delivers continuous
AC 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.
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 using transformers, 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 invents the AC Motor
www.sciencemuseum.org.uk
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 produces an electric
field.
4. Moving electrical charge (current) produces a
magnetic field.
Maxwell predicts
Electromagnetic
Radiation
An electromagnetic wave exists when the changing magnetic field
causes an electric field which then causes another magnetic field,
and so on forever.
These oscillating fields together form an electromagnetic wave.
An electromagnetic wave will travel at 186,000 miles/sec. and
continue on forever until absorbed.
Wikipedia.com
Heinrich Hertz demonstrates
in 1888 the existence of
electromagnetic radiation
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
Sources
► The
Sciences- 5e, Trefil and Hazen
► A History of Great Inventions, James Dyson
► http://www.physclips.unsw.edu.au/jw/electr
icmotors.html