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Magnetism
Magnetic Force
Definition of Magnetic Field
Cross Products
Bar Magnets
Horseshoe Magnets
The Earth’s Magnetic Field
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Magnetism
Magnetic Force
Definition of Magnetic Field
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Magnetism
Magnetic Force
Properties of a magnetic field
Definition of a Magnetic Field
A magnetic field is a set of vectors found everywhere in
space. These vectors describe the interaction between
moving charges and other moving charges.
What magnetic fields are not …
1.
2.
3.
4.
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They are not themselves charges.
They are not electric (or any other) fields.
They are not contained in charges.
They are not forces.
Magnetism
Magnetic Force
Magnetic fields are caused by the movement of charge.
Magnetic fields also put forces on moving charges.
Magnetic fields are in addition to electric fields.
Magnetism is NOT the same as electricity.
Magnetic objects have North and South poles.
For every North pole there is an attached South pole.
You can’t have one without the other.
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Magnetism
Magnetic Force
Cross Products
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Magnetism
Magnetic Force

B

A 
C
1. Point the fingers of your
right hand in the direction
of the vector A.
2. Curl your fingers toward
the direction of the vector
B.
3. The cross-product vector
C is given by the direction
of your thumb.
This movie is availabale as a separate file.
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Magnetism
Magnetic Force
Bar Magnets
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Magnetism
Magnetic Force
N
S
N
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Bar Magnets get
their magnetism
from spinning
electrons. The
spin axis of these
electrons align.
This is called
Ferromagnetism
Magnetism
Magnetic Force
The direction of the
magnetic field vector at
any point in space is
easily found by using a
smaller magnet. This
smaller magnet we call a
compass.
N
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S
Magnetism
Magnetic Force
If we draw the field lines
that correspond to these
field vectors, they would
look like this.
N
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S
Magnetism
Magnetic Force
Horseshoe Magnets
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Magnetism
Magnetic Force
If we draw the field lines
of a bar magnet, they
look like this.
N
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S
Magnetism
Magnetic Force
The Earth’s Magnetic Field
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Magnetism
Magnetic Force
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Magnetism
Magnetic Force
The magnetic field of the
earth is stretched by the
solar wind.
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