Waves

The ancient Greeks, originally those near the city of Magnesia, and also the early Chinese knew about strange and rare stones (possibly chunks of iron ore struck by lightning) with the power to attract iron. A steel needle stroked with such a "lodestone" became "magnetic" as well.
Around the year 1000 A.D., the Chinese found that such a needle, when freely suspended, pointed north-south. The magnetic compass soon spread to Europe. Columbus used it when he crossed the Atlantic ocean, noting not only that the needle deviated slightly from exact north (as indicated by the stars) but also that the deviation changed during the voyage.
Around 1600, William Gilbert, physician to Queen Elizabeth I of England, proposed an explanation: the Earth itself was a giant magnet, with its magnetic poles some distance away from its geographic poles (i.e., near the points defining the axis about which the Earth spins).
By convention in the United States today, the compass arrow points in approximately the direction of the North Geographic Pole. And by convention (unrelated to the first convention), the compass arrow is labeled a magnetic north pole, which is attracted to (points to) the magnetic south pole of a bar magnet, often marked with an “S” or with blue color. Using the fact that opposite poles attract, this means that the compass arrow must be attracted to a magnetic south pole in the Northern Hemisphere on Earth.

Magnets always have two poles, come in various shapes, and attract or repel other magnets.
There are permanent magnets, temporary magnets, and electromagnets.
- Magnetite is a magnetic material found in nature. It is a permanent magnet, but it is relatively weak.
- Most permanent magnets we use today are manufactured and are a combination or alloy of iron, nickel and cobalt. Rare-earth permanent magnets are a special type of magnet that can have extreme strength.
- An example of a temporary magnet is soft iron, which retains magnetism for a relatively short time.
Magnets have two poles, called the north (N) and south (S) poles. Opposite poles attract and like poles repel.
Elements such as Iron, Cobalt, and Nickel make great permanent magnets. Copper and Aluminum are mostly nonmagnetic.
Magnetic domains can be induced (forced to align) by applied magnetic fields. This is why a nail, which is normally
nonmagnetic becomes magnetic when touched by a magnet.

An interesting characteristic of magnets is that when you cut a magnet into parts, each part will have both N and S poles. In other words, it is not possible to create a magnetic monopole.
All magnets have a North-seeking pole (N) and South-seeking pole (S). In a compass, the side marked (N), often colored red, will point toward the Earth's 'North' magnetic pole, the magnetic pole that lies in the geographic North pole. However, because the north pole of the magnet is attracted to this pole it is actually a geomagnetic south pole. The geomagnetic south pole is not located right on top of the geographic north pole but is actually several hundred miles away. Similarly, the geomagnetic north pole is located a few hundred miles away from the geographic south pole.

A solenoid is a simple electromagnetic device consisting of a coiled electric wire, wrapped in the shape of a helix. When electric current is passed through the wire, the solenoid acts like a magnet with N and S poles at the ends of the helix.
Since it is hollow, a solenoid can draw an ferromagnetic rod into the helix. This effect is handy in creating switching or locking devices. Another use of a solenoid is in the creation of an electromagnet. When an iron rod is permanently placed inside the solenoid, the metal greatly increases the magnetic effect.

Electromagnets are made by winding an insulated wire around an iron core and then passing electric current through the wire. The solenoidal ('spiraling') electric current causes the atoms in the core to align along the axis, which turns the core into a magnet.
The direction of the current determines which end of the electromagnet becomes the north (N) pole and which becomes the south (S) pole of the electromagnet.
A major feature of an electromagnet is that you can adjust the strength and direction of the field, and turn it on and off. This allows for a number of applications, including doorbells, loudspeakers, coil gun, and maglev train.
Strong electromagnets are often used in areas of heavy industry to move large pieces of iron or steel. They are commonly employed in junkyards, where a crane with a huge electromagnet is used to pick up, move and drop old, junked cars.
A simple electromagnet can be made by wrapping an insulated wire around an iron nail and using a battery to provide the electric current.

Creating a simple electromagnet using a nail

Electromagnetic lock
- An electromagnetic lock be used to lock a door by creating a strong field in an electromagnet that is in contact with a magnetic plate. As long as there is current through the electromagnet, the door remains closed and locked.
- Another type of electromagnetic lock uses an electromagnet to extend a plunger between the doors, making it nearly impossible to open the door until the electromagnet releases the plunger.
Doorbell ringer
- An old-fashioned doorbell used an electromagnet that was rapidly turned on and off to pull a clangor against a bell. Thus, an electromagnet can be used to pick up a piece of iron and then drop it someplace else.
Crane uses electromagnet to pick up junked car
In a coil gun, a ferromagnetic projectile is first drawn in and then expelled by an eletromagnet.

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