Download Module II – Discovering Electrical Phenomena

5.12 MAGNETISM p163
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Magnet = is an object that can
attract another object.
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Contains iron, cobalt and/or nickel
Magnetism = is the phenomena
caused by magnets
History of Magnetism
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Observed by the Greek 600 BC
Put into use by the Chinese
Used by magicians and sailors
Illusions…..
Always, sometimes or never????
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Iron is sometimes magnetic.
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ST
EST
AST
Iron is made up of domains that are like tiny
magnets.
When the iron is not magnetized, the
domains are not aligned. Their magnetic
effects cancel out.
When the iron is magnetized, the domains
line up.
The greater the number of aligned domains,
the stronger the magnet.
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ST
EST
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Magnets will always have a north
and a south pole.
If the magnet breaks, each piece will
have a north and a south.
Categories of Substances
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Three Categories
 Magnetic
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Ferromagnetic
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Non-magnetic
Magnetic
Invisible fields
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Attract or repel
Object that has a field and that can
attract some other objects.
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Example: horseshoe magnet
Ferromagnetic
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Not a magnet
Is attracted by a magnet
Can be magnetized (by a magnet)
Must contain iron, nickel or cobalt
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eg: paper clip or nail
Non-Magnetic
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Is not attracted by a magnet
Example: glass, plastic, or wood
Magnetism
 is a property that makes certain
materials attract or repel.
 Permanent Magnet
 is always magnetic
 creates a magnetic field
 Ferromagnetic
 Attracted by a magnet,
 can become magnetized
 Must contain Iron, Nickel, Cobalt
 Nonmagnetic
 Never attracted by a magnet
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Important Facts about Magnets
Facts:
 All magnets have two
poles, a North (N) and a
South (S). They are
known as dipoles.
 Fields are infinite in size &
3-Dimensional
Repulsion
Important

Similar poles repel &
opposite poles attract.
Attraction
Important
Poles
N attracts South
S attracts North
N repels North
S repels South
Opposites
attract
Likes
repel
Mapping Magnetic Fields
Remember
•the lines
never cross
 Around
a magnet
there are lines of
goes from North to South
force•Always
that
have direction and strength
•Closer the lines, stronger the attraction
(magnetic field).
Compass
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The needle of the compass is
magnetic
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Important
Example #1
Example #2
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North
end
Red Tip of needle is North
Red Tip will always be attracted towards the
South end.
Tip of arrow
Is North
therefore
It is attracted
to South
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Opposites attract (i.e N & S)
Likes Repel (i.e. S & S or N & N)
Magnetic Field
 Arrows always go from north to south
(outside magnet)
 Lines of force never cross
 The closer the lines, the stronger the
field
Compass
 Red portion of compass needle is a
North ended magnet and is always
attracted to the South end(of another
magnet)
Why the Compass Works
Why the Compass Works
Aurora Borealis
NASA – explanation and history of northern lights
http://youtu.be/ZqqTiiCgyUc
Making own compass
http://youtu.be/ZGaQXx5lDWo
Origins of Magnetism of Matter
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Scientists believe
that magnetism
comes from
spinning electrons
around the nucleus
of the atom.
When atoms clump
together they form a
domain.
Origins of Magnetism of Matter
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Similar electron spins
produce a strong
domain, where as
opposite electron
spins cancel one
another out and
produce a weak
domain.
If enough domains
align in the same
direction, this will
create a magnetic
field.
5.13 How to Magnetize an Object
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Bring the ferromagnetic substance in
contact with another magnet.
Bang the ferromagnetic substance
(example: striking a nail repeatedly).
Heat up the substance and cause
the domains to align.
Run electric current through the
ferromagnetic substance.
Please note that all of these
methods can also de-magnetize a
magnet.
Some cool magnet stuff
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How to make a compass
http://youtu.be/pjQU3yClEKU
Ferrofluid
http://youtu.be/HQzEBBmF960
http://youtu.be/1EuyZ5Lml4k
Use the magnet boxes to help you draw the
magnetic fields present in the following situations.