Transcript Electromagnetism - Smyrna Middle School

Electromagnetism
Kevin Bracken
Smyrna Middle
6-3
2007
Magnets and Magnetism
• Can stick to each other.
• Can stick to some types of metals.
• Can stick to other objects without actually
touching the object.
Properties of magnets
• Discovered more than 2,000 years ago.
• Found in Magnesia, so the Greeks called it
Magnetite.
• Today any material that attracts iron or
materials containing iron is called a
magnet.
• All have two poles, exert forces and are
surrounded by a magnetic field.
Magnetic Poles
• The parts of the magnet where the
magnetic field is strongest.
• On a bar magnet, the poles are on each
end.
• Always occurs in pairs.
• The pole that points north is called the
north pole.
• The pole that points south is called the
south pole.
Magnetic Forces
• The force of repulsion or attraction
between the poles of a magnet is called
the magnetic force.
• Like poles repel. (Push away)
• Opposite poles attract. (Come together)
Magnetic Fields
• The field lines can be drawn from the north
pole to the south pole of a magnetic.
• The closer the field lines the stronger the
field.
What Makes Materials Magnetic
• It depends on the atoms.
• If the atoms in a domain are all lined up
the material is magnetic.
• Iron, nickel, and cobalt are all magnetic.
Losing Alignment
• Dropping
• Hitting it too hard
• Heating
Making Magnets
• Aligning domains can cause an object to
become magnetized.
• You can do this by taking a magnet and
rubbing it in one direction over and over
again on an object.
Domains
The photo on the left shows what happens to the field lines when domains
are not aligned, the photo on the right shows a magnet with its domains
aligned.
Half a Magnet?
If you cut a magnet in half you end up with
two smaller magnets, each with a north
and south pole.
This is because of those tiny domains inside
every magnet.
Types of Magnets
• Ferromagnets
– Nickel, Cobalt, and Iron
Magnetite is a naturally occurring
Ferromagnet.
Electromagnets- have an iron core and has
an electric current.
Temporary and Permanent
• Temporary easy magnetize, and easy to
lose magnetism.
• Permanent- difficult to magnetize and
difficult to lose magnetism.
– Alnico-made from
• Nickel, Cobalt, Aluminum
Earth as Magnet
• Earth’s solid inner core is surrounded by a
fluid outer core.
• This flow of metals creates an electric field
and acts like a bar magnet.
• This helps to create the northern lights.
Magnetism from Electricity
• Maglev trains have been created that use
magnets and electricity to move.
The Discovery of Electromagnetism
• Hans Christian Oersted (1820).
• Held a compass near a wire carrying an
electric current.
– This threw off the orientation of the compass
needle.
– When he reversed the current the magnetic
field reversed.
Take a break
• …..to be continued tomorrow…..
Using Electromagnetism
• You can increase the strength of the magnetic
field by adding a current carrying wire.
• Solenoids
– Coil of wire that produces a magnetic field when
carrying an electric current.
• Electromagnets
– Magnet consisting of a solenoid wrapped around an
iron core.
• Heavy Lifting
– Electromagnets can be turned off and on.
Ways to Increase the Strength of
an Electromagnet
• Increase the number of loops
in the solenoid.
• Add or increase the size of the
iron core.
• Increasing the current in the
wire.
Uses (Applications) of
Electromagnetism
•
•
•
•
Doorbells
Electric Motors
Galvanometers
Lifting Heavy Objects
Electricity From Magnetism
• Faraday wrapped a current carrying wire
around half of an iron ring and wrapped
the other side with a wire connected to a
galvanometer.
• The only activity he recorded was at hookup and disconnection.
• Electric current was produced in the
second wire only when the magnetic field
was changing.
Some of Faraday’s Set-Ups
What Faraday Learned
• Adding more coils increased
the electric current.
• Moving the magnet faster
produces a greater electric
current as well.
Applications of Electromagnetic
Induction
• Generators
– Often used as back-up power.
– The coil of wire is turned.
– Produces alternating or AC current.
• Generating Electrical Energy
– Huge magnets are turned to create the power.
– Used by nuclear, hydroelectric, and fossil fuel plants.
• Transformers
– Used to step-up (increase) or step-down (decrease)
voltage.
How Electricity Gets to Your Home