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Magnetism
Three Properties of Magnets1. 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/outdoor-activities/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/videos/extreme-engineering-season-1-shorts-maglev-train.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
3. Aurora Borealis
4. Levitation
5. Hans Oersted
b. surrounds magnets and exerts a force on other objects
d. magnets contain north and south ones
a. light show at the north pole of the earth
c. when an object raises above a surface
d. predicted that magnets were affected by current
WORD ASSOCIATION
Magnet + Levitation = _____________
________ ________ rule = prediction
Opposites = _________________
To push away is to = __________________
Temporary Magnet = ____________________
MAGLEV
Right Hand
attract
repel
ferromagnet
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 flow2. Strength of the magnet is increased by adding more loops of the wire around the cylinder3. It still has a north and a south pole4. Attracts other magnetic materials5. 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 speakersElectric motorsTelephones
Focus on SPEAKERSThe 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 rotate toward empty.
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 / DCAlternating 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 direct-current 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.
