Magnetism
Three Properties of Magnets
1. Magnets have poles; a north pole and a south pole.
2. Magnets exert forces; they can push or pull other magnets.
3. Magnets have a magnetic field around them. This is the
area where the force acts.
Magnetic field - surrounds magnets and
exerts a force on other objects
Magnetic fields
also have a
direction.
The field lines are closest at the ends of the magnet -- the
POLES - every magnet has a north and a south pole
Oddly shaped
magnets still have a
north and a south
Magnets either attract or repel each other
South poles are attracted to north poles
Like poles repel
Unlike poles attract
What happens when you bring a
compass near a bar magnet?
The north indicator of the compass will
point toward the south pole of a
magnet.
This is also why a compass points
north, it's lining up with the earth's
magnetic poles.
Sometimes the field
completely flips. The north
and the south poles swap
places. Such reversals,
recorded in the magnetism
of ancient rocks, are
unpredictable.
They come at irregular
intervals averaging about
300,000 years; the last one
was 780,000 years ago.
Are we overdue for
another? No one knows.
The magnetic North Pole is responsible for more than just the
direction a compass points. It's also the source of the aurora
borealis, the dramatic lights that appear when solar radiation
bounces off the Earth's magnetic field.
This happens at the South
Pole as well. In the southern
hemisphere, the lights are
called the aurora australas.
Make your own compass
http://adventure.howstuffworks.com/outdooractivities/hiking/compass2.htm
Magnetic Domains = groups of
atoms with aligned poles
Magnets can be temporary (like
the needle used in the compass).
This nail has its atoms aligned,
but the effect is only
temporary. You can get this affect
by rubbing the nail on a magnet.
Neat fact: Hitting the nail can
demagnetize it, you are basically
scrambling the atoms.
A permanent magnet is an object made from a material that is
magnetized and creates its own persistent magnetic field.
An everyday example is a refrigerator magnet used to hold
notes on a refrigerator door.
Metals that are magnetic: nickel, iron, cobalt
Things that are not magnetic: aluminum, plastic, glass
Ferromagnetic - a substance such as iron in which the
magnetic moments of the atoms spontaneously line up with
each other, making a large net magnetic moment.
Ferromagnets lose their ferromagnetism when heated above a
specific temperature , because the thermal energy melts the
magnetic alignment.
What else can cause a ferromagnet to lose its magnetism?
In 1820, it was discovered that a compass
needle is affected by an electric current.
Several responses to Hans Christian
Oersted's observation:
No way!!!
For realz?
Liar!
Unbelievable!
He went further to
propose that the
direction of the field
changed with the
direction of the current.
Maglev Trains
Magnetic + Levitation =
maglev
Maglev vehicles “float” over
an electromagnetically
powered fixed steel
guideway and are propelled
by the current with no
motors, wheels, moving
parts or additional energy
sources. The system is
environmentally friendly,
energy efficient and runs in
all weather conditions.
http://dsc.discovery.com/vide
os/extreme-engineeringseason-1-shorts-maglevtrain.html
A rule was created to predict the direction of
the magnetic field.
It is called The Right Hand Rule
Field can either be
clockwise or
counterclockwise,
depending on the
direction of the
current.
WORD CHECK
1. Magnetic Field
2. Poles
d. magnets contain
north and south ones
a. light show at the
north pole of the earth
3. Aurora Borealis
4. Levitation
c. when an object
raises above a surface
5. Hans Oersted
b. surrounds magnets
and exerts a force on
other objects
d. predicted that
magnets were
affected by current
WORD ASSOCIATION
MAGLEV
Magnet + Levitation = _____________
Right Hand
________
________ rule = prediction
attract
Opposites = _________________
repel
To push away is to = __________________
ferromagnet
Temporary Magnet = ____________________
Word Rhymes
Each of the words rhymes with something from this section of
notes ...
1. Wield _________________
2. Goal ________________
3. Mouth ________________
4. Lo mein __________________
5. Sickle _________________
6. School _________________
7. Car _______________
9. Course ______________
10. Right _________________
Word Rhymes
Each of the words rhymes with something from this section of
notes ...
1. Wield ____field_____
2. Goal _____pole________
3. Mouth ___south_________
4. Lo mein ___domain_____________
5. Sickle ____nickel_______
6. School __rule__________
7. Car ____bar________
9. Course Stew ___horseshoe_________
10. Right ___light__________
What is an ELECTROMAGNET?
A temporary magnet made by wrapping a wire coil
carrying a current around an iron core.
Solenoid - a single wire wrapped around a
cylinder
In a car or truck, the starter solenoid is part of an automobile
starting system. The starter solenoid receives a large electric
current from the car battery and a small electric current from the
ignition switch.
When the ignition switch is
turned on, the small electric
current forces the starter
solenoid to close a pair of
heavy contacts, thus
relaying the large electric
current to the starter motor.
Properties of Electromagnets
1. Temporary, only magnetic when there is a current flow
2. Strength of the magnet is increased by adding more loops of
the wire around the cylinder
3. It still has a north and a south pole
4. Attracts other magnetic materials
5. When current is turned on, the magnet may be attracted (or
repelled) to other magnets. The movement can then be
converted to mechanical energy to work
Examples:
Stereo speakers
Electric motors
Telephones
Focus on SPEAKERS
The loudspeakers in your radio, television or stereo system
consists of a permanent magnet surrounding an electromagnet
that is attached to the loudspeaker membrane or cone.
By varying the electric current
through the wires around the
electromagnet, the speaker cone
moves back and forth.
The resulting vibration of the speaker
cone will create sound waves,
including that from voice and music.
How to make an electromagnet...
These same principles are used
to make equipment that can lift
large objects by switching a
magnet on and off.
What is a galvanometer?
These are devices that are used to measure electric current.
Gauges in your car use these devices to measure how
much gasoline is in the tank, or the water temperature in the
engine.
A float in the fuel tank is
attached to a senor that
sends a current to the
gauge
galvanometer. As the
level changes, so does
the current. The
changing current
causes the needle to
What is an electric motor?
Device that changes electrical energy into mechanical energy causing something to move:
-- blades of a fan
-- wheels of a car
-- hair dryers
-- blenders
http://www.sparkmuseum.com/MOTORS.HTM
Electric Motors - convert electrical energy to
mechanical energy
This motor runs a current through a wire. The wire is
then attracted and then repelled by the magnet
underneath - this will cause it to SPIN
How to Build a Simple Electric Motor
Even Simpler: Magnet, Wire, Battery
What is a GENERATOR?
Converts mechanical energy to electrical energy
AC / DC
Alternating Current - reverses the
direction of the current in a regular
pattern
Direct Current - flows in only one
direction, this comes from a battery
Before the turn of the
century, Thomas Edison
and Tesla were engaged in
a battle known as the War
of Currents. Edison was a
staunch proponent of directcurrent electricity, while
Tesla was an advocate of
alternating current.
~LINK~
What is a transformer?
A device that increases or decreases the
voltage of an AC current.
Magnets used in
Technology
MRI - magnetic resonance
imaging.
Magnetic resonance imaging (MRI) is a
non-invasive imaging method that uses
radio waves and a powerful magnetic
field to produce images of the body.
MRIs are great for looking at all the
organs and soft tissue parts of the body
that X-rays don't see. Patient must
remain still in one position during the
MRI scan. Most MRI scans take about
30 minutes. Anything metallic must be
removed before taking the MRI.
Magnets are placed in speakers.
If you’ve ever hooked up a stereo
system, then you know that there are
two output wires for each speaker—
typically a black one and a red one.
Essentially, the amplifier is constantly
switching the electrical signal,
fluctuating between a positive charge
and a negative charge on the red wire.
Since electrons always flow in the same
direction between positively charged
particles and negatively charged
particles, the current going through the
speaker moves one way and then
reverses and flows the other way.
This alternating current causes the polar
orientation of the electromagnet to
reverse itself many times a second.
Fluctuations cause sound.
Magnets Can be
Used to Move
Objects
When you turn off
the power, the
magnet stops
working (and you
can drop the object)
Quiz Time - check out this page first
http://www.magnet.fsu.edu/education/tutorials/index.html
Check out the *Science Demonstrations link for some
neat tricks with magnets.
Or check out this video about "LINEMEN" who repair
power lines: http://www.youtube.com/watch?v=7gl-_Liz_0o
1. All magnets are surrounded by an invisible force called the
________________ _______________
2. The north pole of one magnet will be attracted to the ______
pole of another magnet.
3. The poles of the earth can move. True or False?
4. In the far north, radiation from the sun is reflected off the
earth's magnetic field and creates patterns of colors. This effect
is known as the ___________ ________________
5. A nail is normally not magnetized. How can you magnetize
it?
6. Who discovered that magnets are affected by electricity?
7. You can make an ______________________ by wrapping a
wire coil carrying a current around an iron core.
8. What car part is attached to your starter and is needed to
start the car?
9. This is a device used to measure electric current.
10. A generator converts ___________ energy into electrical
energy.