24-1 Magnets: permanent & temporary

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24-1 MAGNETS: PERMANENT
& TEMPORARY
General Properties


Hang the bar magnet from
the thread, observe what
happens…….
Positions itself in the N-S
directions - magnet is
polarized
 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
elements
– 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
Electromagnetism


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
Solenoid
 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
Electromagnet
Strength of the field is proportional to the current in
the coil
 Increasing
the number of loops increases the strength
Electromagnet

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
electromagnet
 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
domains
 Shown
as arrows that are random in
direction
 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

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