# Magnetism - Physics at SPASH

Magnetism The Basics The first magnetic stone was discovered by the Greeks around 600 BCE and was called a Lodestone. Today, we call it Magnetite The magnets we manufacture and use today always have two poles, north and south. Like

poles repel Opposite poles attract Magnetic Field Lines Magnets create magnetic field lines. Field lines travel from the North to South pole of a magnet

Field lines are concentric loops Field lines never overlap A stronger magnet will have more field lines Which magnet is stronger??

Ferromagnetism Normal Magnetism Objects that are ferromagnetic are strongly attracted to magnets and can become permanently magnetized All permanent magnets are ferromagnetic Examples: Iron,

Nickel, Cobalt, and Gadolinium Temporary Magnets A temporary magnet only acts as a magnet when it is inside a magnetic field. As soon as it is removed from the magnetic field, it no longer acts as a magnet. Touching a ferromagnetic material to a permanent magnet will create a

temporary magnet. Permanent Magnets A permanent magnet does not require an external magnetic field. The object always acts as a magnet. You can create a permanent magnet by placing a ferromagnetic material inside loops of strong electric current. This

is how a magnetizer works. Neodymium Magnets A VERY strong permanent, rare-earth magnet Rare-Earth naturally Nd2Fe14B magnets are manufactured; they do not occur

Compass A compass needle always points along (in the direction of) magnetic field lines. A compass needle is actually a small magnet, so its north pole is attracted to the south pole of any other magnet Earth as a magnet Earths

molten outer core contains iron. Convection currents within the molten iron generate current (moving charge) which creates a magnetic field The South magnetic pole is near the North geographic pole The North magnetic pole is near the South geographic pole

Domain Theory Why are only some materials magnetic? All atoms/molecules have a magnetic moment (tiny magnet) Materials are ferromagnetic if large regions, or domains, of atoms/molecules have the SAME magnetic moment

In magnets, all domains point in the same direction Video Link How to demagnetize a magnet Misalign the domain directions Heat up the magnet

Drop the magnet or apply a large force to it Curie The Temperature temperature at which a permanent magnet stops working as a magnet (domains become misaligned)

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