# Electromagnetism by ewghwehws

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```									Electromagnetism
Electromagnetism
• 1820, Oersted finds that a current carrying
wire will cause a compass needle to deflect
• Implication: the current carrying wire itself
behaves like a magnet (since it can exert a
force on another magnet… like a permanent
magnet would)
• Let’s use field theory to understand what’s
happening
Magnetic Field for a coil of wire
called a solenoid
Magnetic Field for Solenoid with an
Iron Core
Another interesting application…
electric motors
Electromagnetism (cont’d)
• 1820, Oersted finds that a current carrying
wire will cause a compass needle to
deflect… so there was a discovery waiting
• 1832, Michael Faraday found that a
changing magnetic field could produce an
electric current… electromagnetic induction
• Principle underlying electric generators
Four Stations
1. Build an electromagnet - design & execute an
experiment to test how the number of coils
affects the strength of the electromagnet
2. Build your own telegraph
3. Build an electric motor - try to determine the
number of rpms of it
4. Measure the voltage and current produced by a
hand-crank generator over a 10 second time
period
NOTE: You must create your own data tables for
stations 1 & 4
Contrasting Electric motors and
generators
• Electric motors – convert electrical energy
into mechanical energy… the motion of
electrons into the motion of something else
• Electric generators – convert mechanical
energy into electrical energy… the motion
of something into the motion of electrons
Transformers
Electrical Transmission
Electrical Transmission
• Transformers only work with alternating current.
• Using direct current will create a magnetic field in
the core but it will not be a changing magnetic
field and so no voltage will be induced in the
secondary coil.
• Using a step up transformer to increase the voltage
does not give you something for nothing. As the
voltage goes up, the current goes down by the
same proportion. The power equation shows that
the overall power remains the same.
• P=V x I Power = Voltage x Current
Electrical Transmission (cont’d)
• Power output is always less than the power input because
the changing magnetic field in the core creates currents
(called eddy currents) which heat the core. This heat is
then lost to the environment, it is wasted energy.
• Electricity is first produced at the power plants and then
sent to step-up transformers where low-voltage electricity
is changed to high voltage to facilitate the transfer of
power from the power plant to the customer. Voltage must
be increased so that the electric current has the "push" it
needs to efficiently travel long distances.
• Ohm’s Law V = I R
Electrical Transmission (cont’d)
• From the step-up transformer, transmission lines carry the
high voltage electric current long distances through thick
wires mounted on tall towers that keep the transmission
lines high above the ground. Insulators made of porcelain
or polymers are used to prevent the electricity from leaving
the transmission lines.
• High-voltage transmission lines carry the electric current to
substations where the voltage is lowered so it that can be
distributed locally on smaller power lines known as
distribution lines.
• Distribution line voltage levels are typically 4 kV or 12
kV. These voltages are reduced one last time at smaller
pole-top transformers to utilization voltages, typically 120
and 240 volts, to make the power safe to use in our homes.
Equipment needed
•   Large nails
•   Strong cylindrical magnets
•   Small nails
•   FOSS equipment
• Circuit boards, coils of wire, wire, batteries, switches,
iron pieces, long wires, battery holders
•   Hand-crank generators
•   Voltmeters
•   Ammeters
•   Foil
•   Scissors
•   Galvanometer, coils, wires, switch

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