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Magnetism
The shadow of electricity
Magnetic Force
Magnets apply forces to each other.
Opposite poles attract, like poles repel.
CPS Question
The magnitude of the force between
magnetic poles
A. is the same at all distances.
B. becomes stronger as the poles come closer.
C. becomes weaker as the poles come closer.
Magnetic Field Lines
Conventions as with electric field lines.
direction is
direction of force
on a north pole
strong field
where lines are
close together
Field lines point from North to South pole.
Group Work
1. What happens to a dipole magnet in a
uniform magnetic field?
B
N
S
Naming the poles
N = northseeking
Earth’s north
pole is a south
pole!
Current Creates Magnetism
An electric current creates a magnetic field.
Look, Ma! No poles!
Vector Direction Conventions
Left
Right
Up
Down
In
Out
Poll Question
If a wire in front of you carries a current from
left to right, what is the direction of the
resulting magnetic field where you are?
I
A.
B.
C.
D.
E.
F.
Board Work
An electric current creates a magnetic field
whose lines circle right-handed around it.
Draw lines for the magnetic field created by
a ring of current.
I
Magnetic Field of Current Ring
N
dipole
field
S
Source: Griffith, The Physics of Everyday Phenomena
Solenoid Magnetic Field
N
S
Source: Griffith, The Physics of Everyday Phenomena
Electrons are Magnets!
spin
Electrons are Magnets!
current
Electrons are Magnets!
magnetic
field
Electrons are Magnets!
N
S
magnetic
dipole
Types of Magnets
• Electromagnets
– currents travel through conducting coils
• Permanent Magnets
– materials whose electrons have aligned spins
or orbits
Moving charges create the fields!