Transcript magnetism ppt

Magnetism
Section 1
Section 1: Magnets and Magnetic Fields
Preview
• Key Ideas
• Bellringer
• Magnets
• Magnetic Fields
• Earth’s Magnetic Field
Magnetism
Section 1
Key Ideas
〉What happens when the poles of two magnets
are brought close together?
〉What causes a magnet to attract or repel
another magnet?
〉How is Earth’s magnetic field oriented?
Magnetism
Section 1
Bellringer
1. Most of us use magnets in our daily life without
thinking about it. Name five places that you use
magnets.
2. If you had two bar magnets and you touched the end
of one bar magnet to the end of the other bar magnet,
what are the two possible outcomes? If you rotated
one of the bar magnets 180°, what are the two
possible outcomes?
3. Explain why a compass is a useful tool for navigation.
Magnetism
Section 1
Bellringer, continued
4. On Earth, there is the magnetic N pole and the
geographic North Pole. According to the picture
above, are they located at the same geographic
location? Where do you think the magnetic S pole
is located?
Magnetism
Section 1
Magnets
〉What happens when the poles of two magnets
are brought close together?
〉Two like poles repel each other. Two unlike
poles attract each other.
• magnetic pole: one of two points, such as the ends of
a magnet, that have opposing magnetic qualities
– All magnets have at least one pair of poles, a north
pole and a south pole.
– It is impossible to isolate a magnet’s south pole from
the magnet’s north pole.
Magnetism
Section 1
Visual Concept: Magnetic Poles
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Magnetism
Section 1
Magnets, continued
• Some materials can be made into permanent magnets.
• A magnetized piece of iron is called a “permanent”
magnet, but its magnetism can be weakened or
even removed.
• Iron is a soft magnetic material.
• It is easily magnetized.
• It tends to lose its magnetic properties easily.
• Cobalt is a hard magnetic material.
• It more difficult to magnetize.
• Once magnetized, it doesn’t lose its magnetism
easily.
Magnetism
Section 1
Visual Concept: Magnetic Materials
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Magnetism
Section 1
Magnetic Fields
〉What causes a magnet to attract or repel
another magnet?
〉Magnets repel or attract each other because
of the interaction of their magnetic fields.
• magnetic field: a region where a magnetic force can
be detected
Magnetism
Section 1
Magnetic Fields, continued
• Magnets are sources of magnetic fields.
• Moving charges create magnetic fields.
• magnetic domains: groups of atoms that all line up
the same way and form small, magnetized regions
within a material
• Magnetic field lines are used to represent a magnetic
field.
– Field lines always form closed loops.
• The magnetic field gets weaker with distance from
the magnet.
Magnetism
Section 1
Magnetic Fields, continued
• Magnetic field lines that are
close together indicate a
strong magnetic field.
• Field lines that are farther
apart indicate a weaker field.
• Magnetic field lines begin at
the north pole of a magnet and
end at the south pole of the
magnet.
Magnetism
Section 1
Visual Concept: Magnetic Field
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Magnetism
Section 1
Magnetic Fields, continued
• Compasses align with Earth’s magnetic field.
– The compass points in the direction that lies along
the magnetic field line at a given point.
– By convention, the pole of a magnet that points
north is painted red.
Magnetism
Section 1
Earth’s Magnetic Field
〉How is Earth’s magnetic field oriented?
〉Earth’s magnetic field lines run from
geographic south to geographic north.
• The pole in Antarctica is a magnetic north pole.
• The pole in northern Canada is a magnetic south pole.
Magnetism
Section 1
Earth’s Magnetic Field, continued
• Earth’s magnetic field has both direction and strength.
• The source of Earth’s magnetism is not yet fully
understood.
– The iron in the core is too hot to retain any
magnetic properties.
– The circulation of ions or electrons in the liquid
layer of Earth’s core may be the source of the
magnetism.
• The sun also has a magnetic field and ejects charged
particles into space.
Magnetism
Section 1
Visual Concept: Earth’s Magnetic Field
Click the button below to watch the Visual Concept.