Download MAGNETIC ATTRACTION

MAGNETIC ATTRACTION
Spring 2008
The Nature of Magnetism
• Magnets are found everywhere…doorbells,
TV’s, computers…
• Magnets were discovered in a region in Greece
called….you guessed it…Magnesia!!!
• They discovered the unusual rock about 2,000
years ago.
The Nature of Magnetism…
• The rock had strange properties…
• It attracted anything that contained iron. This rock is
the mineral we call magnetite.
• Magnetism is defined as the attraction of a magnet to
another object.
• About 1,000 years ago…people discovered that
magnets have another unusual property…
The Nature of Magnetism
• If you swing a rock freely from a
string…one part of the rock always points
in the same direction…toward a specific
star…northern star (also called the
lodestar).
• For this reason…magnetic rocks are
sometimes called lodestones.
Magnetic Poles
• Any magnet has 2 ends – each is a magnetic pole.
• This is the area where the magnetic effect is the
strongest…just like one end of a magnetite rock always
points on direction…
• One pole will always point north and therefore it is called the
north pole. The other is, of course, the south pole.
• The north and south pole are direct opposites.
Attraction...
• What happens when you bring 2 magnets together?
• If you bring the 2 north poles together – they repel or push
away from each other. The same is true for 2 south poles.
• If you bring one north and one south pole together – they
are attracted to each other.
• So…alike poles repel…unlike poles attract.
• Any material that exerts a magnetic attraction is considered
a magnet.
So What’s the Big Deal??
• The Maglev
Train…magnetically
levitating train…
• Runs solely on
magnetism…
• Fast, efficient, and does
NOT harm the
environment…
What happens if???
• What happens if you break a magnet?
• Do you get one south pole and one north pole magnet?
• No…actually… when a magnet is broken in will develop
another pole on that end…so it will always have a north
and a south end.
• If you break them again…the same process would happen.
MAGNETO…
• The character Magneto
from the “X-Men”
comic series has the
ability to create
magnetic fields and use
magnetic force to control
objects.
So, What are Magnetic Fields???
• Magnetic forces are exerted all
around a magnet, but is
strongest at the poles.
• The region of magnetic force
around an object is called the
magnetic field.
• A magnetic field allows
magnets to interact without
actually touching.
Magnetic Fields…
• Magnetic field lines map
out the magnetic field
around an object. These
lines spread out from pole
to pole and curve around
the magnet to return to the
other pole. See the diagram
at left.
Magnetic Properties…
• Depend on the structure of the atoms making up the object.
• A spinning electron (negatively charged) creates a magnetic
field.
• A bar magnet has what is called a magnetic domain. It has
a strong representation and therefore a stronger attraction.
• Materials that have a very strong attraction to a magnet are
said to be ferromagnetic material. These are items made
from iron, nickel, cobalt, samarium, etc.
Creating Magnets…
• You can make a magnet by taking ferromagnetic material
and place it in a magnetic field or rub a magnet against it.
The field has to be relatively strong for this to occur.
• Once the domains line up – your magnet is created.
• This is why you can magnetize a paperclip to pick up other
paperclips.
• Unfortunately, most of theses are only temporary.
Permanent magnets are much more difficult to make and
hold their magnetism indefinitely
Destroying Magnets…
• You can destroy a magnet field by striking the magnet very
hard or dropping it as well.
• This knocks the domains out of alignment.
• Heating a magnet will also destroy the magnetism. Above a
certain temperature, materials lose their ferromagnetism
properties altogether.
Compass…
• Defined as a device that has a magnetized needle than can
spin freely.
• The needle usually points north.
• This occurs because the Earth acts like a giant magnet.
Earth has an enormous magnetic field surrounding it – just
like a huge bar magnet.
• A scientist named Gilbert believed the center of the Earth
contained magnetic rocks…unfortunately, he was wrong,
but it was a great start.
More on Compasses…
• Scientists now know that the
magnetism is partially caused by the
circulation of molten material made
from iron and nickel.
• The simple fact that Earth has a
magnetic field explains why a
compass actually works.
• The magnetized needle aligns its
domain with that of the Earth –
therefore pointing North.
Magnetosphere…
• Earth’s magnetic field extends
into space.
• Electrically charged particles
affect Earth’s magnetic field.
• The Van Allen Belts are
located about 1,000-25,000
km above the Earth’s surface.
• In this particular region,
electrons and protons move at
very high speeds.
Magnetosphere…
• Solar Winds from the sun also
carry electrically charged particles to
Earth.
• The region where Solar Winds
shape Earth’s magnetic fields is
called the magnetosphere.
• This is a continual process as Earth
rotates on it’s axis.
• When the particles move too close to
Earth’s surface, we see the Aurora
Borealis or Northern Lights in the
sky. (called the Southern Lights in
the Southern hemisphere…)
Earth’s Magnetic Field…
• Earth’s magnetic directionality has changed throughout
history.
• From time to time…the poles will switch due to the magnetic
field created by the Earth.
• The last time the poles switched was about 780,000 years
ago.
• Scientists are perplexed as to why this occurs, but believe it
has something to do with the change in flow of the magnetic
molten material at Earth’s core.
It’s Electric!
• Electrons carry a negative charge.
Protons carry a positive charge.
• When these charges flow through a
wire or other object the create an
electric current.
• Electric currents are defined as the
flow of a charge through a material.
• The amount of charge that passes
through the wire in a unit of time is
measured in amperes (an amp).
It’s Electric!
• An electric current produces a
magnetic field.
• The direction of the current
determines the direction of the
magnetic field.
• If the current reverses, so does
the field.
Electric Circuits…
• Electric currents do not
automatically flow through
wires.
• Current only flows through
electric circuits.
• An electric circuit is a complete
path through which electric
charges can flow.
• All electrical devices contain
electric currents.
Electric Circuits…
• All circuits have the same basic
features.
• A circuit has to have a source of
electrical energy.
• Next, circuits have devices that are
run by electrical energy…like a
light bulb converts electrical energy
to electromagnetic energy (it gives
off light) and thermal energy (it
gives off heat).
• Lastly, electric circuits are connected
by conducting wires and a switch.
Conductors…
• Electric currents do not flow through
all objects.
• Electric currents move freely
through objects called conductors.
• Examples of conductors: copper,
silver, iron, and aluminum are all
good conductors.
• In a conductor, some of the electrons
are only loosely bound to their
atoms. These electrons are able to
move around and generate an
electric current.
Light switch???
• Did you ever wonder why a
light comes on when you flip a
switch?
• Electrons are not created every
time you flip a switch – they
are always there in the
conductors of the circuit.
Insulators…
• Insulators are a different kind
of material where charges are
not allowed to move freely.
• The electrons are bound tightly
to their atoms and do not flow
easily.
• Examples of good insulators:
rubber, glass, sand, plastic, and
wood.
Electrical Resistance…
• A resistor uses electrical energy as it
interferes with, or resists, the flow of
charge.
• Resistance is the opposition to the
movement of charges flowing
through a material.
• Resistance depends on an objects
atomic structure. (Like trying to
cross a crowded room…the more
collisions…the more energy is
converted.)
Light Bulb…
• Edison used resistance when
developing his light bulb.
• He needed a material that conducted
electrical currents, but that would
offer enough resistance to make the
material heat up and glow.
• He tried a variety of items: copper
wires, silk fibers, shredded corn husks
to name a few.
• He eventually used the metal
tungsten for the purpose.
SUPERCONDUCTORS!!!
• A superconductor is a material that
has no electrical resistance.
• This normally occurs at very low
temperatures. (That’s the problem!)
• There is no loss of energy and
therefore the electrical device is much
more efficient.
• They also strongly repel magnets.
• A strong magnetic field would
destroy a superconductor.
Electromagnets…
• Solenoids is a current carrying wire
with many loops.
• The solenoid creates a magnetic field
at the center of the coil.
• The 2 ends act like poles and can be
turned off or on by a switch.
• If you place a ferromagnetic
material inside a solenoid – the
magnetic field is increased.
• A solenoid with a ferromagnetic core
is called an Electromagnet!
Electromagnets…
• Electromagnets are strong magnets
that can be turned off or on.
• These are ideal for lifting large pieces
of scrap metal like at a junk yard.
• When the switch is on – the magnet
is activated. When the switch is
turned off – the magnet is no longer
magnetized.
• You can increase and decrease the
power of the electromagnet by
increasing or decreasing the number
of coils of the solenoid or by using a
stronger ferromagnetic material.
FINITO!!
That’s All Folks!!