2. Magnetism Legend has it that magnetism was first discovered some 2000 years ago when an elderly shepherd named Magnes was herding his sheep across a rocky valley when the iron nails in the soles of his sandles stuck to the rocks there. We have learned a lot since then.

3. Magnetic fields Try breaking a magnet. What happens? Do a quick magnet lab – show like poles repel, opposites attract Out from north pole, into south pole http://phet.colorado.edu/en/simulation/magnets-and-electromagnets

4. Suppose you have two iron bars that look alike, but only one of them is a magnet. How can you determine which is the magnet only by investigating their interaction with each other?

5. The true magnet will stick to any part of the iron bar. How to tell which is which? Make a T shape with the bars. Only the magnet placed at the midpoint of the non-magnet will stick. Can you think of other ways to tell which one is the magnet?

6. Magnetism Iron filings lie along magnetic field lines. All magnets have a dipolar (two lobed) field. That means that magnets have north poles and south poles. If you cut a magnet in half, each half becomes a magnet with two poles. In the language of physics, we say that the magnetic field is dipolar. There is not such a thing as a magnetic monopole, at least that we have found. Electric monopoles do exist. A charged particle is an example of an electric monopole.

7. Magnetic monopoles? Field lines would start on a magnetic charge (a magnetic monopole). Does not seem to exist.

8. Notice the pole of the earth’s magnetic field that is in the northern hemisphere The magnetic field of an electron is ultimately what is responsible for permanent magnets

9. Some types of magnetism Ferromagnetic materials are strongly attracted to magnets. The atoms contain electrons which are all spinning in the same direction, giving the atoms strong polarity (like little magnets). Atoms tend to line up parallel to each other within domains of the material. A magnetic field can force the domains to line up, and the material itself can become magnetic. (Ex: iron, nickel, cobalt, steel) Paramagnetic materials are weakly attracted to magnets. The atoms of these substances contain electrons most of which spin in the same direction, but not all. These metals can become very weak magnets. (Ex: aluminum, gold, copper) Diamagnetic materials are magnetically neutral, because the electrons in the atoms are spinning in equal numbers in opposite directions. Individual atoms have some polarity (more electrons spinning around one side than the other) and will move in response to a magnetic field. This effect is used in Magnetic Resonance Imaging (MRI). http://www.worsleyschool.net/science/files/magnet/types/ofmagnetism.html

10. Magnetic domains - ferromagnetism High temperature will destroy macroscopic alignment of domains http://www.magnet.fsu.edu/educ ation/tutorials/java/domains/index.html http://www.magnet.fsu.edu/educ ation/tutorials/java/domains/index.html

11. Magnetic domains A magnetized surface changes the reflectivity depending on the magnetic domains. The light also changes in polarity. These effects are called the Magneto Optical Kerr Effect (MOKE) and they allow us to photograph the magnetic domains using a special microscope called a Kerr-effect microscope.

12. Ferromagnetism What does it take to demagnetize a ferromagnet? Hit it or heat it: Either one randomizes orientation of domains. Hitting: creates shock waves that disrupt atom alignment Heating: increases thermal fluctuations, making orientation of atoms more random The lowest energy configuration of a ferromagnet is when the atoms are all lined up. If you add energy to the system, the atoms can realize higher energy configurations, and don’t have to all line up. Above a certain temperature, there is no magnetization.

13. Ferromagnetism Geological example: Molten rock is magnetized as it cools in the Earth’s magnetic field. The discovery of magnetized moon rock suggests that the moon once had magnetic poles. http://blogs.discovermagazine.com/80beats/2009/01/20/moon-rock-suggests-the-young-moon-had-a-fiery-core-and-a-magnetic-field/