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Magnetism
Ch. 12
How does Magnetism Compare to
Electrical Charges?
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Like Charges repel, unlike charges attract
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Like Poles will repel, unlike poles attract
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These forces allow both magnetic poles
and electric charges to “line up” with
opposite forces—kind of like a force pair
How are they different?
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Magnetic Poles always come in pairs (like
heads and tails on a coin)
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Electric charges can come in pairs but they
can also be separated (protons in the
nucleus, electrons outside)
Magnetic Field
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These are regions of magnetic influence
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Areas where objects are pulled by a magnetic
force
Surround an electric field—cannot have one
without the other.
What causes Magnetism?
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It is caused by constant electron motion
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Electron move in 2 ways (just like the Earth)
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They spin on their axis (like a top)
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They revolve around the nucleus
Current Carrying Wire
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Do wires that carry current have a magnetic
field?
You can’t have one without the other
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By definition, one moving charge makes a
magnetic field
Therefore, a whole current of electric
charges will make a larger magnetic field
This magnetic field goes in circles around
the wire (see p. 196)
If the current changes direction the circles
will also change directions
Why are some metals metallic and
some not?
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Depends on magnetic domains (p. 195)
If the atoms are aligned they are magnetic
If they are not aligned they are not
magnetic
If a magnet is dropped on a hard floor, what
will happen?
Electromagnetic Induction
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Anytime you change a magnetic force,
(distance or strength), you induce an
electromagnetic field
-Move a magnet closer or further away
from an electric current
-Or if you change the amount of electric
current, an EM field is produced
What is this? Why?
Earth is a giant magnet
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One end of every magnet will spin to the
north if possible.
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This has been used for over 2,000 years to
help guide travelers.
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A compass is a freely spinning magnet.
William Gilbert
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Responsible for fine-tuning the idea of a
compass in the early 1600s
First to suggest that Earth was a magnet.

Said the Earth has a giant bar magnet
running through its center, and the magnetic
poles were near the geographic poles
North or South Pole
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A compass always points which direction?
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Doesn’t that mean it should be attracting to
it’s opposite pole?
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So what is actually near the geographic
North Pole?
How a compass works
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A compass needle points north because it
is strongly attracted to a magnetic south
pole
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The magnetic poles are not straight up and
down, but rather they are tilted
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See Diagram on Board