Magnetism
Force
• Attractions exist between some metals
• Force is most concentrated at the ends of
the metal object
• Ends are called Poles (North and South)
• N pole points north when magnet hangs
free
• Opposite poles attract and similar poles
repel
Magnetic Fields
• Area around magnet that the force acts
• Can be represented with field lines much
like electric field lines
• Closer lines; stronger field
• Lines point in direction that a N-pole test
would point (toward South)
Earth As A Magnet
• Earth acts as if it has a large bar magnet
imbedded within it
magnetic pole
geographic pole
S
N
geographic pole
magnetic pole
Earth’s Magnet
• Magnetism of the earth does not line up
with the axis, so the magnetic pole is not
the same as the geographic pole
• Magnetic declination – amount that the
compass is off from truly pointing North
Magnetic Materials
• Ferromagnetic – any material attracted to a
magnet or that can be magnetized
• Atoms of these materials can be thought of
as tiny magnets
• Groups of atoms in the same area are
called domains
• If all domains line up in the same direction,
the material becomes magnetized
Creating or Destroying
• Dropped or heated, loses magnetism
• If magnet is broken just becomes smaller
magnets
• Created by induction (rub with magnet)
• Induced from earth (point in same direction
as earths magnet and hit it)
Electromagnetism
• Similarities between magnetism and
electricity:
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–
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Two types
Likes repel, opp attract
Fields
Can be created by rubbing
Inverse square law
Oersted’s Discovery
• Whenever electrons move through a
conductor, a magnetic field is created in
the region around it
• Field lines are in circles around the
conductor
• As distance from conductor increases, field
gets weaker (lines farther apart)
Right Hand Rule
• Conductor held in right hand with thumb
pointing in the direction of the current, the
fingers point in the direction of the
magnetic field
Coils
• Magnetic fields around a conductor can be
intensified by bending a wire into a loop
• More loops, greater the intensity
• Solenoind – large # of loops in a coil
• Field within the coil is straight and points
in one direction
Right Hand Rule
• Coil grasped with right hand and fingers
curled in the direction of the current, the
thumb points in the direction of the
magnetic field
• Ends of coils like the poles
• Direction of current reversed, poles
reversed
S
N