Magnetism Another one of natures mysteries… Paul Hsu Period 5

Ancient Times… 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, and around 1000 the Chinese found that such a needle, when freely suspended, pointed north- south.

Magical Needle… 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 ones.

Magnetism Magnetism is the force where objects are attracted or repelled to one another. The term magnetism is derived from Magnesia, the name of a region in Asia Minor where lodestone, a naturally magnetic iron ore, was found in ancient times. Iron is not the only material that is easily magnetized when placed in a magnetic field; others include nickel and cobalt. Magnetism is basically the movement of charged particles, such as protons and electrons. It is very closely related to electricity, which is the movement of electrons.

Magnetic Poles Every magnet has two poles. This is where most of its magnetic strength is most powerful. These poles are called north and south or north-seeking and south seeking poles. The poles are called this as when a magnet is hung or suspended the magnet lines up in a north - south direction.

Magnetic Poles (cont.) When the north pole of one magnet is placed near the north pole of another magnet, the poles are repelled. When the south poles of two magnets are placed near one another, they also are repelled from one another. When the north and south poles of two magnets are placed near one another, they are attracted to one another.

Magnetic force travels from the north poles to the south poles.

Earth as a Big Magnet. The north pole of a magnet or compass always points to the north, which means that the magnetic north is actually near the south pole.

Electricity and Magnetism In the early 1800s, scientists were studying magnetism and electricity simultaneously. It was discovered that a magnetic needle could be deflected by an electrical current passing through a wire. (basis for motors) Also the reverse, moving a magnet near a wire induced an electrical current. (basis for turbines in power plants)

What Causes Magnetism? At the atomic level, the electrons have a natural spin. This gives them the property of being a natural bar magnet. Magnetism is measured in terms of magnetic moments. A magnetic moment is a vector quantity that depends on the strength and orientation of the magnetic field, and the configuration of the object that produces the magnetic field.

What Causes Magnetism? (cont.) In 1927, German physicist Werner Heisenberg gave a detailed explanation for a molecular magnetic fields theory. He used the then newly-developed quantum mechanics. Afterwards, other scientists predicted more complex atomic arrangements of magnetic moments, with diverse magnetic properties.

Applications The electro-magnet is the basis of the electric motor and the transformer New magnetic materials used in computers create small areas of magnetism. These are either parallel or perpendicular to the overall magnetic field and thus indicates a 0 or a 1. Used in particle accelerators to accelerate charged ions to desired energy levels. They also keep the particles focused and traveling in the correct path.

Applications (cont.) Magnetic tape is used in video cassettes, credit cards, and floppy disks, where the data is stored magnetically. Most importantly… used in most televisions to accurately guide electrons to the screen, making what seems like a flawless image.