Magnets
were discovered independently by the people in China and Greece.
They had found that natural lodestone magnets attracted iron. The
Chinese also found that a piece of loadstone would point in a north-south
direction if it was allowed to rotate freely. This was how they told
fortunes and also what they used as a guide for building. By A.D.
1200, the Chinese and Europeans had realized the uses behind this magical
stone and they began using it on their ships as compasses to steer.
In 1269, a French soldier named Pierre de Maricourt mapped the magnetic
field around a lodestone sphere with a compass. It was then discovered
that a magnet has two poles. And later in 1600, the earth itself
was recognized as having two poles by a physician of Queen Elizabeth I
of England, named William Gilbert.
Hans Christian
Oersted in 1820, a Danish physicist observed that an electric current flowing
in a wire caused the needle of a magnetic compass to rotate. His
discovery proved that electricity and magnetism were related. Then, in
the early 1830's, the English scientist Michael Faraday and the American
physicist Joseph Henry independently discovered that a changing magnetic
field induced a current in a coil of wire. This discovery led to the electric
motor meters which would eventually bring about electric powered radio
and television.
A magnet attracts iron, steel, nickel, and certain other
materials. The attracted materials then become magnets themselves
in a process called magnetization. For example, if you were to place
a nail near a magnet, it would become magnetized and would then attract
a second nail. Magnetization occurs because the magnet causes particles
called electrons in the atoms of the nail to align along the magnet's lines
of force. The atoms with aligned electrons then act like tiny bar
magnets themselves.
There are 3 main types of magnets,
1. Temporary magnets
2. Permanent magnets and
3. Electromagnets
Temporary magnets are just that, temporary. They
are made of such materials as iron and nickel. These materials are
known as soft magnetic materials because they usually don retain their
magnetism once removed form a strong magnetic field. For example,
the nail we spoke of earlier, once you remove the nail form the strong
magnet its near it will lose its magnetic ability to attract other nails.
Permanent magnets are magnets that keep their magnetism after they've been removed from a strong magnetic field. They are therefore known as hard magnetic materials. Examples are alloys (mixtures) of iron, nickel or cobalt mixed with other elements. Alloys that contain the rare-earth elements have produced some of the strongest permanent magnets. Examples of the rare-earth elements are: samarium and neodymium.
There are a few soft magnetic materials that can be made
into weak permanent magnets. An iron needle for a compass, for example,
can be permanently magnetized by stroking it in one direction with a magnet.
Electromagnets are temporary magnets produced by electric
currents. The simplest electromagnets consist of electric current
flowing through a cylindrical coil of wire called a solenoid. One
end of the solenoid becomes the north pole and the other becomes the south
pole. The reversal of the current can cause the poles to switch position,
and if the its shut off, the solenoid will lose its magnetism.
Yes,
the earth really does have a north pole! The earth really does have
a north pole! The earth is actually a giant magnet with two poles,
yeah you guessed it, a north pole and a south pole. These are near
the geographic North and South poles. The north magnetic pole attracts
the north pole of the compass needle, but is actually the south pole of
the earth. Huh? (Remember opposites attract?) Similarly, the
south magnetic pole is the north pole of the earth magnet because it repels
the north pole of a compass needle.
.
opposites attract
The magnetic field as the surface
of the earth is known as the geomagnetic field and is created by the
inner structure of the earth. Beneath the crust (the outermost portion
we live on) there is a rocky mantle. Under this mantle is a dense
core made up of a solid inner part and a liquid outer part. Its believed
by scientists that the motion of electric charges in the liquid outer core
produces the geomagnetic field.
drilling
to the earth's core in Hawaii
Magnets have many uses in our everyday life as well as
in our homes. In our homes attractive forces between magnets keep
our cabinet latches closed, as knife racks and most importantly used for
displaying all your artwork on the fridge! 
However, the most important use of magnets in your home
are the ones found in electric motors. Believe it or not it's
electromagnetic and permanent magnets that help keep your blenders, vacuums,
cd players and washing machines all running. They are also termed
"heads" when referring to your VCR. These "heads" record and
read information on tapes covered with many tiny magnetic particles. The
magnetic field of a recording head makes the magnetic particles on the
tape form patterns that another type of head can read. The second
head then transforms the magnetic patterns into an electric signal in which
you can view your favorite episode of "Friends" or The Simpson's.
In industry and business mostly electromagnetic
powered devices will be found, such as cranes, cutters, fax machines, computers,
etc. Powerful cranes (as the one below) are commonly found in wrecking
yards to help move scrap iron and steel from old cars as well as move metals
for recycling.
It's also not uncommon nowadays to find electrified transportation. They as well rely on magnets in electric motors. Systems like this include: subways, trolleys, monorails, cable cars, escalators, elevators and moving sidewalks. They also add conveniences to our cars by aiding in electric windows, door lock, and windshield wipers. And lastly, electromagnets also produce radio waves in radar systems, an important navigation aid for ships and planes.
As the years continue to grow on us,
so does technology. Magnets are also being used in medicine.
There are certain type of magnets called bending magnets.
They are powerful and are used to help control beams of atomic particles
which is boosted into high speed devices called particle accelerators.
A procedure most everyone has heard of, an MRI (Magnetic Renaissance Imaging)
also relies on magnets. Here, the person lies in between two magnets
and the magnetic fields which cause some of the domains in the human body
to align such as the heart, brain, spine and other internal organs.
Physicians are then able to observe any magnetic fields generated by some
of the organs.
Scientists have discovered that many
animals, including pigeons, honey bees, salmon, tuna, dolphins and turtles
are able to detect the earth's magnetic field and may use it to help find
their way. Particles of magnetite have been found in the body tissues
of these animals. They suspect the particles form part of a system
that sense the geomagnetic field.
Certain species of bacteria found
in the water have also been found that use the geomagnetic field to find
their preferred habitat. Each bacteria use the particles as tiny
compass needles to guide them along the electromagnetic field.
What
do Magnets Do?/ Magnetic poles
A magnet with two poles, such as a bar magnet, is called a magnetic dipole. One end points to the north & is considered the north pole, the end that points to the south is considered the south pole. The best way to visualize these two poles is to cut a magnet in half, creating a north pole and a south pole.
Lines
of force are three-dimensional, surrounding a bar magnet on all sides.
When opposite poles of a magnet are brought together, the lines of force
join up and the magnets pull together.
.
If the north pole of a magnet is brought
near the south pole of another magnet, the magnetic force will pull the
magnets together. However, two north pole or two south poles brought
together would repel each other. In other words, like repels like
and the old saying, opposites attract! Why does this happen?
That would be explained by what is known as the magnetic field. The
magnetic field around a magnet is where the force of the magnetism can
be felt. It is invisible, but you can get an idea of what it looks
like by this simple example.
Take a magnet and place a piece of paper over
it. On top of the paper (and above the magnet) sprinkle
iron fillings. The fillings arrange themselves
along the lines of the magnetic force, making the lines visible.
A magnetic force can also be thought of as set of imaginary
lines called lines of force. These lines are thought of as
going out from the north pole of a magnet, looping around, and returning
to the magnet at its south pole. The magnetic field is the strongest
at the poles and is where the lines lie closest to each other. This
explains why a compass works. The needle of a compass is actually
a magnet. It normally points north along one of the earths magnetic
field lines. But a strong bar magnet placed next to the compass will cause
the needle to point along on of the bar magnet ‘s field lines. 