Download - Magnetism
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MAGNETISMMAGNETISM
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The Earth
Magnetic Poles
North and South
Geographic Poles
North and South
Earth is a giant magnet.
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Magnetic Declination
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InclinometerAn example of an inclinometer showing the Earth’s magnetic inclination
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Compass PointsThe direction of compass points in United States
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Types of Magnets
LOADSTONE
BAR
UCOIL ALNICO
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Natural Magnet
Material is Magnetite or Iron Oxide (Fe2 03)
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Magnets
A very strong magnet can be made with a coil of wire and the flow of an electric current.
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Alnico
An extremely strong Alnico permanent magnet with keeper
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Theory of Magnetism
Molecular and Electron Theories
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Creating Magnets
The picture shows that a screwdriver does not pick up paper clips.
Methods used to create a magnet
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Creating MagnetsStroking using a permanent magnet
However, after stroking the screwdriver with a magnet, the blade itself becomes magnetic and attracts the paper clips.
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Flux
Magnetic lines of force
Strongest at the poles
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Removing Magnetism
Heat is one way to remove magnetism.
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Laws of Magnets
Poles attract or repel
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Like Poles Repel
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Laws of magnets shown by flux lines
Unlike poles attract Like poles repel
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Stray Lines of Force
Controlling stray lines using a keeper
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Magnetic Lines of Force
Notice how the materials are affected
Soft iron is a material that distorts flux
Magnetism will pass through any material
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Electromagnetism
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Electromagnets
A 30-foot diameter electromagnet
used in research for a superconductor
A large electromagnetused to lift scrap metal
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ElectromagnetsThe source of electromagnetism is electricity (current) flowing through a coil of wire.
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Electromagnets
A coil of wire can be made into a magnet by passing an electric current through it.
Without electricity, there is no magnetic force
Electric current applied to a coil creates a magnetic field
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Electromagnetic Strength
Increase the number of coils. Increase the electric current flowing through
the coil. Add an iron core in the center of the coil.
How can an electromagnet be made stronger?
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Electromagnetic Strength
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The left hand rule to determine North Pole
NORTH POLE SOUTH POLE
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Making a Magnet
An example of a very strong magnet
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The magnet is strong enough to lift this 50 pound engine cylinder head.
The coil of wire has been attached to a 12 volt DC power source making an extremely strong magnet.
Making a Magnet
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Saturation
Saturation KneeY- Axis
Increasing
Magnetic
Force
Y
X- Axis Increasing Electric Current
X
Saturation of a magnetic field occurs when an increase of electric current flow does not increase the strength of the magnetic field as shown by the graph. The knee of the curve is the point that saturation occurs.
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MAGNETIC COIL LOSSES
Copper losses - resistance of copper coils.
Hysteresis - magnetic flux inducing a current in the core.
Eddy currents - magnetic polarity of the iron core is rapidly changed by an AC current causing friction and heat between the molecules
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ELECTROMAGNETIC DEVICES
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Electromagnetic Devices
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Electromagnetic Devices
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MAGNETIC TERMS
Flux - Invisible lines of force. Poles - North and South where force is
strongest. Permeability – The ability of a material to
conduct lines of force. Residual Magnetism – The ability of a
material to hold its magnetism for a long time.
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MAGNETIC TERMS
Ferromagnetic Material – A material easy to magnetize. (i.e., Iron Steel, Cobalt, Perm-alloy, and Alnico)
Paramagnetic Material- A material that can be slightly magnetized.
Diamagnetic Material – A material that is very difficult to magnetize.
Magnetic Laws – Simply stated: Like poles repel and unlike poles attract.
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Review
What are the poles of a magnet? Name the magnetic lines of force. List five types of magnets and their two
families. List the laws of magnets. Explain two methods for making a magnet.
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Review
Explain two theories of magnetism. Name five different types of devices that are
associated with electromagnetism? List three magnetic and three nonmagnetic
materials. What will remove magnetic lines of force?