Magnetism

1. Magnetism

2. Magnetic Properties • Like magnetic poles repel • Unlike magnetic poles attract • Magnetic field – space around a magnet in which a magnetic force is exerted.

3. Origin of Magnets • Early Greeks discovered a rare ore in a region of Turkey called Magnesia. • In the 12th century, the Chinese found that a single stone made of this ore if suspended will always point toward geographical north

4. Origin of magnets • Lodestones – leading stone used by navigators to always know the direction of travel. • Chinese invented the first compass which they called lodestones.

5. Magnets • N pole – North seeking geographic north • S pole – South seeking geographic south

6. Compass • A magnet that is free to move • Responds to Earth’s magnetic field

7. What are some statements that we just made that may seem contradictory? • The _________ pole of the earth’s magnetic field is located close to the _________ geographic pole. • The N pole of a compass needle is attracted to the earth’s _________ magnetic pole. south north south

10. Magnetic declination • Difference between magnetic and geographic poles.

12. Magnetic or Not

13. Ferromagnetic elements • Are strongly attracted to magnets

14. Paired electrons with opposite magnetic spins cancel

15. Unpaired electrons with same spins cause magnetic fields to reinforce for an atom

16. Ferromagnetic elements • Are strongly attracted to magnets • Have many unpaired electrons spinning in the same direction to produce identical magnetic fields. • Most common are Fe, Co, and Ni

17. Why aren’t all nails magnets? • Attach paper clips to your magnets until they will hold no more. • Remove the magnet by holding the top paperclip and taking the magnet away. • What happened? • Drop the paperclips. Try to pick up one with another to see if they are still magnetic.

18. Why aren’t all nails magnets? • Domains – large groups of ferromagnetic atoms whose magnetic fields are aligned. • Randomly oriented in unmagnetized substances. • Align themselves with an external magnetic field. (magnetic induction)

20. Iron for Magnets • Hard ferromagnetic materials (alloys) make better permanent magnets than soft iron because their magnetic domains are hard to align, but once they are, they will stay aligned even without the magnetic field.

21. How does dropping a magnet weaken it? • The magnetic domains of some atoms become misaligned and therefore weaken the magnetic field of the magnet.

22. How will a magnet be affected by breaking it in two? • Breaking a magnet will create two magnets. Both with north and south poles still.

23. How will heating a magnet affect it? • Increases the thermal molecular motion causing some of the atoms to become misaligned and weakening the magnetic field.

24. Show What You Know • Ferromagnetic materials a) are strongly attracted to magnets b) include iron, cobalt, and nickel c) have many unpaired electrons, with identical spins d) all of these 2) Magnetic monopoles a) would have north or south poles alone b) do not exist c) both a and b d) neither a nor b

25. 3) Microscopic regions of atoms whose electron spins are the same - a) are called domains c) are always aligned b) exist in all substances d) all of these 4) Breaking a magnet in two a) destroys its magnetic properties b) makes two smaller magnets 5) Which of these actions will not damage the polarity of a permanent magnet? a) dropping it b) heating it c) breaking it in half d) none of these