1. THE PROPERTY OF A MATERIAL/OBJECT TO ATTRACT OTHER OBJECTS MADE OUT OF IRON, MAGNETITE, OR STEEL Magnetism

2. Magnets and Technology Computers use them to read and write data Your speakers and headphones use them Credit cards and ATM cards store data on magnetized strips Junkyards use them to lift scrap metal They are used in many security systems

3. Two Categories Permanent:  Retains its magnetic properties all the time regardless of whether it’s near another magnetic object. Objects that can be magnetized:  When brought close to another magnet  i.e. a refrigerator magnet There are no liquid magnets  This is because magnetic effects come from the small scale organization of atoms within a material.  Disrupting this orderly arrangement (i.e. heating) destroys magnetic effects.

4. Poles All magnets contain two magnetic poles.  They have an opposite polarity, called north and south pole.  If you cut a permanent magnet in half, each will have a north and south pole. You can separate + and – charges but not N and S poles of a magnet.

5. Attraction and Repulsion When two magnets are close, they exert an attractive/repulsive force depending on how the poles are aligned. Opposites attract!!!  When north and south are put together, the magnets will attract each other.  North-north or south-south will repel. The force between two magnets at shorter distances increase more rapidly causing the forces to become very strong and hard to separate.

6. Attraction and Repulsion (cont.) Because magnets are dipoles (two poles), the strength decreases rapidly as they are separated. Opposite magnetic forces on the two ends of abar magnet can create a torque (rotational motion) that causes the magnet to twist/rotate.

7. Force Field An organization of energy in space that creates a force on any receptive matter that passes within its ‘influence’.  Gravity is an example.  The sun’s gravitational field causes forces on each planet The force between magnets acts through a magnetic field.  The poles create a magnetic field that extends outward in the surrounding space.  Other magnets ‘feel’ forces through their interaction with this field.  This is a non-contact force.

8. The Magnetic Field It describes the strength and direction of magnetic forces around a magnet.  A compass is a freely spinning magnet sensitive to magnetic fields.  Each location we place a compass tell us the direction of the magnetic force.  The red end typically is the magnetic north pole.

9. Magnetic Field Drawing Uses lines and arrows to represent the force exerted on the north magnetic pole.  They point into south poles and out of north poles.  The closer the field lines the stronger the magnetic force.  Field lines never cross  Field lines always make closed loops Our planet has a magnetic field approximately aligned with its north-south axis.  Migratory birds sense this field and use it (remember, The Core)  Humans use a compass.

10. Compass Why does a compass point north?  Earth’s north geographic pole is a south magnetic pole.  People labeled the north magnetic pole of a magnet as the pole that pointed north. Earth’s magnetic field completely reverses itself every million years or so!

11. Diamagnetism, Paramagnetism and Ferromagnetism: Diamagnetism:  The effect of materials to slightly repel magnets of either polarity.  Silver, lead, and copper Paramagnetism:  Slightly attract magnets of either polarity  Aluminum, Magnesium and Tungsten These are substances that can become magnetized and experience strong magnetic forces in the presence of external magnets.  Paperclips  Iron, Cobalt, and nickle

12. Magnetic Domains The property that makes iron ferromagnetic is that it only takes a small amount of energy for an iron atom to flip its magnetic axis. Groups of Iron atoms form these domains in which atoms within a single domain have a similar magnetic alignment.

13. Magnetic Domains When an external magnet is brought near iron, magnetic domains attracted to the magnet gain atoms and grow because the iron atoms easily change their magnetic orientation. Domains repelled by external magnets easily lose atoms and shrink and vice versa Ferromagnetic materials are crucial to many technologies such as motors and generators.

14. Each magnet has a north-seeking and south-seeking pole Exert a magnetic force on the space around them = magnetic field Lines closer together – stronger field Where is the field strength the greatest on a magnet?

15. Nature of a Magnetic Field Produced by the motion of an electric charge (current)  Current carrying wire can produce a magnetic field (macroscopic)  Electrons around an atom produce a tiny current and thus a magnetic field (microscopic) SI unit for magnetic field is the Tesla Different examples of magnetic fields

16. Magnetic field (cont.) Two e- spinning in same direction = stronger magnetic field Two e- spinning in different direction = zero magnetic field Common magnets are made of iron, nickel, and cobalt.  The spin of their e- do not cancel => magnets

17. Magnetic Domains Individual atoms align to form magnetic domains, a cluster of aligned atoms. How can a magnet become weaker? How does a magnet attract a piece of metal that is not magnetized?

18. Electric Currents and Magnetic Fields A current-carrying wire will produce magnetic fields in a pattern of concentric circles When wire is made into loops the magnetic field bunches up. More loops = more magnetic field = electromagnet  (made stronger by adding nail/ iron core)

19. Practical applications of electromagnets Maglev trains – page 569, http://www.o-keating.com/hsr/maglev.htm http://www.o-keating.com/hsr/maglev.htm Stereo speaker, http://electronics.howstuffworks.com/speaker3.htm http://electronics.howstuffworks.com/speaker3.htm Alarm systems Junkyard crane MRI, http://electronics.howstuffworks.com/mri2.htm http://electronics.howstuffworks.com/mri2.htm

20. Magnetic Forces on moving charged particles A charged particle must move relative to the magnetic field in order to be affected by the magnetic field A charged particle that is moving perpendicular to a magnetic field will be forced upward

21. Force of a Magnetic Field on a moving e- The force that a magnetic field places on a charged particle is …  greatest when e- move perpendicular to field lines  Zero when e- move parallel to field lines

22. Magnetic Forces on Current-carrying wires If a moving charged particle is deflected by a magnetic field, so will a wire that contains moving e- A wire will be forced …  up if current is flowing one direction  Down if current is flowing in opposite direction We see this exhibited when using a compass under a wire.

23. Meters Galvanometer-detects current When calibrated it can measure current (ammeter) or voltage (voltmeter)

24. Motors By modifying a galvanometer you can make an electric motor http://electronics.howstuffworks.com/motor1.htm

26. Investigation When we moved a compass around the magnet during the experiment yesterday, what occurred?