Transcript Magnetism_and_Electromagnetism_Review

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The two smaller magnets will have their own
north and south poles
You get two separate magnets, NOT a north
“magnet” and a south “magnet”
This is due to the direction of the domains
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On its poles
Magnets have two poles:
A north pole
A south pole
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Electrons
Electrons spin in orbit around the nucleus
A moving electron produces a magnetic field
This movement makes each atom like a tiny
bar magnet
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The magnetic field
This allows magnets to interact without
touching
Magnetic field lines start at one pole and
return to the opposite pole
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A magnetic domain is a cluster of atoms
whose magnetic fields are all lined up the
same way
This makes an object magnetic
If the domains are not lined up, the object
is not magnetic
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Magnets will attract when two OPPOSITE poles
are brought together
North and South
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A ferromagnetic material
Some ferromagnetic materials are:
Iron
Nickel
Cobalt
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By rubbing a ferromagnetic material with one
pole of a strong magnet
By placing a ferromagnetic material in a
strong magnetic field
Attaching a ferromagnetic material to an
electric circuit
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Magnets repel when two LIKE poles are
brought together
North and North
South and South
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The solar wind is a
stream of charged
particles ejected from
the upper atmosphere
of the sun. It mostly
consists of electrons
and protons.
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Particles from the solar wind travel along the
magnetic field lines
If they come close enough to Earth, they
interact with the atmosphere
This causes the bright colors
An aurora is only seen near the poles because
that is the only place where the magnetic
field lines come close to Earth
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The angle between geographic north and
magnetic north
This is different depending on where you are
on Earth
Magnetic declination changes over time
because the magnetic poles move very slowly
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Drop it repeatedly
Strike it hard
Heat it
All of these cause the domains to move in
different directions
This causes the magnet to lose its magnetic
properties
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An electric current
produces a magnetic
field.
Remember that an
electric current is the
flow of electrons.
Remember also that
the movement of
electrons is what
creates a magnetic
field.
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A current carrying coil of wire with many
loops
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Increase the current in the solenoid
Add more loops of wire
Wind the coils of wire closer
Use a stronger ferromagnetic material for the
core
Induced emf
 A current can be produced by
a changing magnetic field
 First shown in an
experiment by Michael
Faraday
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A primary coil is connected
to a battery
A secondary coil is
connected to an ammeter
Electromagnetic Induction
 When a magnet moves toward a
loop of wire, the ammeter shows
the presence of a current (a)
 When the magnet is held
stationary, there is no current
(b)
 When the magnet moves away
from the loop, the ammeter
shows a current in the opposite
direction (c)
 If the loop is moved instead of
the magnet, a current is also
detected
Electromagnetic Induction –
Results of the Experiment
 A current is set up in the circuit as long as there is
relative motion between the magnet and the loop
 The same experimental results are found whether the
loop moves or the magnet moves
 The current is called an induced current because it is
produced by an induced emf
Applications of Faraday’s Law –
Apnea Monitor
 The coil of wire attached
to the chest carries an
alternating current
 An induced emf
produced by the varying
field passes through a
pick up coil
 When breathing stops,
the pattern of induced
voltages stabilizes and
external monitors sound
an alert
Application – Tape Recorder
 A magnetic tape moves past a
recording and playback head
 The tape is a plastic
ribbon coated with
iron oxide or
chromium oxide
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Application – Tape Recorder, cont.
 To record, the sound is
converted to an electrical
signal which passes to an
electromagnet that
magnetizes the tape in a
particular pattern
 To playback, the
magnetized pattern is
converted back into an
induced current driving a
speaker