Transcript What is Magnetism?

Chapter 17
Magnetism
What is Magnetism?
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Causes attractive and repulsive forces
Magnetic properties are due to the motion of
electrons
Properties of Magnets
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A permanent magnet is a material that keeps its
magnetic properties.
If a material is magnetic, it has the ability to exert
forces on magnets or other magnetic materials
nearby.
Properties of Magnets
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All magnets have two
opposite magnetic poles,
called the north pole and
south pole.
If a magnet is cut in half,
each half will have its own
north and south poles.
Problem Solving Scenario…
Dear Scientist,
I own a jewelry store and recently I have made a lot of money
using magnets to make earrings, necklaces, and even
bracelets. Unfortunately, I only have one big magnet left, but I
need to make 3 different pieces of magnetic jewelry. Since I
only make money if my jewelry is magnetic, I was wondering if
breaking the big magnet into smaller pieces will damage the
magnet and make it non-magnetic, or if breaking the big
magnet will actually make a few smaller magnets.
Please respond as soon as possible!
Thanks,
Julie Magnets
Properties of Magnets
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Magnetic forces can pass through many materials with
no apparent decrease in strength.
Magnetic Field Lines
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The force points away from the
north pole and towards the south
pole.
Magnetic Fields
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The force from a
magnet gets weaker as
it gets farther away.
Magnetic Field Lines
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A compass needle is a magnet that is free to spin.
A compass needle aligns with the local magnetic field
Earth’s Magnetism
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Studies of earthquake waves reveal that the Earth’s core is
made of hot, dense molten metals.
Huge electric currents flowing in the molten iron produce
the Earth’s magnetic field.
https://www.youtube.com/watch?v=Rv7zT953290&authuser=0
Check In!
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In your notebook, answer the following
questions:
1. Magnets have _____ & _____ poles
 2. Magnetic force is due to the movement of
_______ in an atom
 3. The force of a magnet gets _______ (stronger
or weaker) as you move farther away
 4. Earth’s magnetic field comes from ______ ___
in its core
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Geographic & Magnetic Poles
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Earth’s geographic North Pole is actually a south magnetic
pole
A compass needle’s “north” end is actually attracted to
Earth’s “south” magnetic pole!
Declination and “True North”
Earth’s geographic
north pole and
magnetic south pole
are not located at the
exact same place, so a
compass will not point
directly to the
geographic north pole.
magnetic declination: the difference between the
direction a compass points and the direction of the
geographic north pole
Declination and “True North”
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Magnetic declination is measured in degrees and is
indicated on topographical maps.
Most good compasses contain an adjustable ring with a
degree scale used to compensate for declination.
Magnetic Declination NOW
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0° 16' E ± 0° 24' changing by 0° 4' W per year
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http://www.ngdc.noaa.gov/geomag-web/#declination
Earth’s Magnetism
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Earth’s magnetic field is
losing approximately 7
percent of its strength every
100 years.
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If this trend continues, the
magnetic poles will reverse
sometime in the next 2,000
years.
https://www.youtube.com/watch?v=XXTEWQdu3aE&authuser=0
Quick Recap
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North and South poles attract (come together)
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North-North or South-South repel (push apart)
Magnetism is due to moving electrons
Compasses have a north pole magnet (red)
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Attracts to magnetic south (which is north pole)