24-1 Magnets: permanent & temporary

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Transcript 24-1 Magnets: permanent & temporary

General Properties
Hang the bar magnet from
the thread, observe what
Positions itself in the N-S
directions - magnet is
 Has
two ends – North seeking
and South seeking
 A compass is a small magnet
free to turn
General Properties
Observe what happens when another magnet is
brought to the different sides of the magnet
 The
two N poles repel as the two S poles
 N and S pole attract
All magnets have two singular poles or Monopoles
 When
magnet is broken in half, magnets orient themselves
in a N & S direction
Simple Magnets
Touch a magnet to a piece of metal (iron nail) and
try to pick up paper clips along the nail
Nail has become polarized (temporarily)
Either end of a magnet will attach to a metal
Permanent Magnets
Made of ALNICO V
 Aluminum
– Nickel – Cobalt – and other rare earth
Magnetic Field
Magnets are a long range force
Invisible “lines” surround the magnet
showing the magnetic field
 Number
of magnetic lines is
magnetic flux
 # of lines is proportional to strength
 Concentrated at the poles
 Lines flow out of the N and into the S
in closed loops
Electric currents through a wire create a magnetic
field perpendicular to the current
First Right hand Rule
of current  Thumb
 Direction of magnetic field  Fingers coiled
 Direction
Magnetic Field near a Coil
A wire looped several times to form a coil and a
current is allowed to flow, the field around all the
loops is always in the same direction
 Long
coil wire consisting of many loops
Magnetic Field near a Coil
When there is an electric current in a coil wire, the
field acts like a permanent magnet
Strength of the field is proportional to the current in
the coil
 Increasing
the number of loops increases the strength
Strength can also be increased by adding an iron
rod inside the coil
 Field
will magnetize the rod
Second right hand rule
 Direction
of magnetic field produced by an
 Curl fingers around loops in the direction of the current
 Thumb is the North pole of the magnet
Magnetic Domains
Each electron in an atom acts like a
tiny electromagnet  generally in
three magnetic elements
 Iron,
nickel, & cobalt
Groups of electrons are known as
 Shown
as arrows that are random in
 Once a magnetic field is present, arrows
aligned and become magnetized
Physics and Earth Science
Iron is found in the oceanic rocks as basalt
As ocean floor spreads, magma is released
Overtime, earth’s magnetic field has changed