Magnets



 Who discovered Magnets?
Pliny The Elder, the Natural History,       described the magnetite rock and he told about the Magnes shepherd´story:
There is a story that a shepherd from the island of Grete was the first to discover lodestone when his crook, which had an iron tip, was pulled towards a stone when he passed over it. The shepherd ´s name was Magnes.


According to another story, Archimedes, the scientist of ancient Greece, is supposed to have pulled the nails out of enemy ships by using lodestone, which resulted in them sinking.



In the past, lodestone was used by sailors as an aid to navigation. They had discovered that when they suspended a piece of magnetite by a thread, it always pointed in a north-south direction. 
What´s magnet?  
All physical objects are made up of molecules, and the molecules of steel and iron have magnetic properties. According to the molecular theory of magnetism, all the molecules are aligned with their North Pole pointing in one direction and South Pole pointing in the opposite direction in a magnetized piece of steel or iron. Whereas, in a piece of steel or iron that is unmagnetized, the poles of the molecules point at various directions at random.
STEEL IRON
What are magnets used for?
This is a question I'll let you answer.  There are hundreds and hundreds of uses which you will discover here at "Magnet Man" and in the links.  Yes, some are used to hold the family's schedule and photos onto the refrigerator door, but that is just one use for magnets.  Magnets were first put to use to help navigate since they would always point in a North / South direction, no matter what the weather was.  
Daniel Boone once said, "I can't say I was ever lost, but I was bewildered once for three days."  Perhaps if he had a compass, his bewilderment would have only lasted a few hours!
For the most part, magnets are used to hold, separate, control, convey and elevate products and to convert electrical energy into mechanical energy or convert mechanical energy into electrical energy.

   
Here's a list of things I've found around the house and in the car that uses magnets or electromagnets to make them work:
Around the house:
Headphones
Stereo speakers
Computer speakers
Telephone receivers
Phone ringers
Microwave tubes
Doorbell ringer solenoid
Refrigerator magnets to hold things
Seal around refrigerator door
Plug-in battery eliminators
Floppy disk recording and reading head
Audio tape recording and playback head
Video tape recording and playback head
Credit card magnetic strip
TV deflection coil
TV degaussing coil
Computer monitor deflection coil
Computer hard drive recording and reading head
Dishwasher water valve solenoid
Shower curtain weights / attach to tub
Power supply transformers

Motors for use in:

 
CD spinner and head positioner
DVD spinner and head positioner
Audio tape transport
VHS tape transport
VHS tape loader
Microwave stirring fans
Kitchen exhaust fans
Garbage disposal motor
Dishwasher
    Pump
    Timer
Refrigerator
    Compressor
    Ice maker dumper
Sump pump
Furnace
    Blower
    Exhaust
Garage door opener
Clothes washer
    Pump and agitator
    Timer
Clothes dryer
    Timer
    Drum turner
Bathroom exhaust fan
Electric toothbrush
Ceiling fan
Pager or cell phone vibrator
Clocks (not the wind-up type or LCD type)
Computer
    Cooling fans
    Floppy disk spinner
    CD spinner
    DVD spinner
    Hard disk spinner
Can opener
    Motor
    Lid holder magnet
Things in the Car:


Starter motor
A/C clutch
Interior fan motor
Electric door locks
Windshield wiper motor
Electric window motor
Side-view mirror adjuster motor
CD player motor
Audio tape player motor
Audio tape recorder and playback heads
Engine speed sensors
Alternator
Starter relay
Windshield washer pump motor

Can you find more?
What types of magnets are there?
There are three main types of magnets:
    Permanent magnets
    Temporary magnets
    Electromagnets
Permanent Magnets
Permanent magnets are those we are most familiar with, such as the magnets hanging onto our refrigerator doors.  They are permanent in the sense that once they are magnetized, they retain a level of magnetism.  As we will see, different types of permanent magnets have different characteristics or properties concerning how easily they can be demagnetized, how strong they can be, how their strength varies with temperature, and so on.
Temporary Magnets
Temporary magnets are those which act like a permanent magnet when they are within a strong magnetic field, but lose their magnetism when the magnetic field disappears.  Examples would be paperclips and nails and other soft iron items.
Electromagnets
                           
An electromagnet is a tightly wound helical coil of wire, usually with an iron core, which acts like a permanent magnet when current is flowing in the wire.  The strength and polarity of the magnetic field created by the electromagnet are adjustable by changing the magnitude of the current flowing through the wire and by changing the direction of the current flow.
Materials used for permanent magnets
There are four classes of permanent magnets:
    Neodymium Iron Boron (NdFeB or NIB)
    Samarium Cobalt (SmCo)
    Alnico
    Ceramic or Ferrite
What is near the Geographic North Pole, a Magnetic North or a Magnetic South?
 

The Earth is a great magnet. Its magnetic field is like a bar magnet at its center.
We know two things:
    1.    If we allow a bar magnet to swing freely on a string, the end that points towards the geographic north pole is called the north seeking pole of the magnet, and is labeled "N" since it is the North magnetic pole of the magnet.  Its opposite end is labeled "S" for South magnetic pole.  This is the convention used to determine the "N" or North end of a magnet. 
    2.    We know that like poles repel each other and unlike poles attract each other.
Therefore:
    The magnetic field created by the molten core of the earth must have a magnetic South pole near the geographic north pole in order to attract the "N" end of our bar magnet and compass needles.  This pole near the geographic north pole is sometimes called the geomagnetic north pole.