1. Magnetism

2. 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

3. 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

4. Which magnet is stronger??

5. 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

6. 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.

7. 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.

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

9. 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

10. Earth as a magnet
Earth’s 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

11. 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

12. How to demagnetize a magnet
Misalign the domain directions
Heat up the magnet
Drop the magnet or apply a large force to it
Curie Temperature
The temperature at which a permanent magnet stops working as a magnet (domains become misaligned)