Download Magnetism- a force of attraction or repulsion due to the arrangement

Magnetism- a force of
attraction or repulsion due to
the arrangement of electrons.
Mag Lev vid
Why are some materials magnetic?
Iron, nickel and cobalt are
magnetic because the
electrons in the material
have the same axial and
orbital spin, creating a net
electrical force.
Cancellation of this effect
occurs in most materials
since the electron
movement is random in
most matter.
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Magnetic Domains- a microscopic
magnetic region composed of a group of
atoms whose magnetic fields are aligned in
a common direction.
There are NO Magnetic Monopoles…
No matter how many
times a bar magnet
is cut in half,
there is always a
north and south
pole, even in the
smallest piece.
Magnets-like poles repel
opposite poles attracts
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All magnets have north & south poles.
North poles attracts South poles,
South poles attract North poles.
North poles repel North poles,
South poles repel South poles.
In general, magnetic fields
originate on North poles and
terminate on South poles.
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Compass
Needles are
Tiny Magnets
Compass needles are
just small magnets
which twist into
alignment with the
Earth’s magnetic field
The Earth’s magnetic field is caused by the
movement of charged particles in the core.
Earth’s magnetic reversals
Magnetic Fields are defined as a
region in which a magnetic force
Magnetic
can be detected.
Fields
Magnetized
Iron filings line up around
bar magnet.
This shows the
the magnetic field.
shape
Like all field forces, greater
distance from the magnet
reduces the field strength
by an inverse square.
of
Just as an electric charge is surrounded
by an electric field, the same charge is also
surrounded by a magnetic field if
1) it is moving and/or
2) if the electron spins are aligned.
Moving Charges, like current in a
wire, creates Magnetic Fields.
Proof: Compasses (bar magnets)
line up in circles around a
wire carrying current.
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Magnetic Field Patterns around a
Current Carrying Wire
What is an Electromagnet?
An electromagnet is a type of magnet
in which the magnetic field is
produced by the flow of current
through a wire wrapped around an
iron core.
The iron is temporarily magnetized
when there is a current.
Electromagnets are widely used as
components of other electrical devices,
such as motors, generators, relays and
speakers.
Making an
Electromagnet
How can we increase the strength
of an Electromagnet?
Electro
magnet
1.Increase number of turns of wire
2. Increase the current and/or
voltage
3. Use more iron in the core
On the flip side, an electric current can be
created in a wire by changing the magnetic
field.
video
Electric current can be
produced in a looped
wire simply by moving a
wire near a magnet or
via versa.
Rapidly changing the
magnetic field induces a
change in the electric
field causing electrons
to move (current is
produced).
The voltmeter reflects the amount of current produced
by the oscillating magnetic field inside the loop.
Electromagnetic Induction
What happens to the
current produced if the
magnetic flux is
Current is
increased?
increased
What will be the ammeter reading if the
coil number is increased to eight?
2 loops = 1 A
4 loops = 2 A
6 loops = 3 A
8 loops = 4 A
2x coils = 2x I
Magnetic Fields exert force on moving
charges and on current-carrying
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conductor.
A wire carrying currentI has charges moving in
it. Therefore, if a current-carrying conductor is
in an external magnetic field, it experiences a
force.
Electric Motors: Convert electrical
energy into mechanical.
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Here’s how: Current creates magnetic field, which interact
with secondary magnetic field (usually a stationary magnet),
causing motion due to the attraction and repulsion between
the two changing fields.
Motor explained
video
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Computers, cell phones, credit
cards and other devices that
store information in the
orientation of magnetic domains
should never be brought near
electric motors.
Since the motor produces a magnetic field, it can
interact with the stored data, causing devices that
store information to lose it.
Never put a magnet near a TV or
computer screen!
Older screens form images by firing a steam of
electrons which negatively charges the screen. The
magnet will deflect the electrons, thus distorting the
image, often permanently.
Opposite of a motor is a generator,
which uses electromagnetic induction to
convert mechanical energy to
electrical energy.
applet
Coils Rotating in a
Magnetic Field Induce
a Current
Video
Step-down Transformer
A transformer is an electrical device
that takes electricity of one voltage and
changes it into another voltage.
Energy in = Energy out
In this step-up transformer, the number of
turns of the coil are increased, thus increasing
current and therefore, voltage. The greater length
of wire create
greater
resistance
but not
proportionately.
Ultimately, the
power is the
only variable
conserved.