Magnetism

1. Magnetism • property of matter in which there is a force of attraction or repulsion b/w like or unlike poles

2. What do we know about magnets? • 2 Magnetically opposite poles: • North Pole and South Pole • Like poles repel and Opposite poles attract • “We’ll get back to this later”

3. What types of things do magnets attract? 1st • “Do magnets attract all metals?” • Magnets only attract objects made of iron, cobalt, or nickel!! • These metals are called the “Iron Triad” • See Periodic Table • You can also only make a magnet out of these 3 metals. • Those “rubber” magnets have iron, cobalt or nickel in them.

5. Magnetic Domains • The molecules of most substances have no orientation to them. • In a magnet, the molecules align themselves in a very specific pattern.

6. Do magnets have to be touching each other in order to have an effect on each other? I wonder why?

7. Magnetic Field • Surrounding all magnets is a magnetic field. • Magnetic Field is the area surrounding a magnet where the magnetic force acts. Magnetic Field Lines

8. Magnetic Field Lines Magnetic Field Lines always move out of the North pole and into the South pole!!

10. What makes the North Pole the North Pole and the South Pole the South Pole? It is not the N and S stamped on them!!!!

11. The North Pole is the pole that the magnetic field lines move out of. The South Pole is the pole that the magnetic field lines move into.

12. Magnetic Field Lines • Magnetic Field lines always move out of the North end and into the South end!!

13. Magnetic Field Lines of Interacting Magnets Lines of Attraction Lines of Repulsion

14. Solving for Unknown Poles Are the field lines attracting or repelling? North ____________ what? attracts

15. Solving for Unknown Poles Are the field lines attracting or repelling? North __attracts______ what?

16. Solving for Unknown Poles Are the field lines attracting or repelling? North ____________ what? repels

17. Solving for Unknown Poles Are the field lines attracting or repelling? North __repels____ what?

18. Determine the unknown pole • North • South

19. Determine the unknown pole • North • South

20. Where are Magnets the strongest? I wise man told me many years ago that “Magnets are strongest at the poles”. That is where the magnetic field lines are the most concentrated.

21. Which of the following metals would not make a very good magnet? • Iron • Cobalt • Aluminum • Nickel

22. What happens if you break a bar magnet in half? Mr. Garay You get 2 bar magnets both with a North and a South pole!!

23. Breaking a Bar Magnet

24. Where is this magnet the strongest? • 1 only • 2 only • 3 only • 1 and 3

25. Where is this magnet the strongest? • 1 only • 2 only • 3 only • 1 and 2

26. If you broke a bar magnet in half and then broke both halves in half again, how many bar magnets would you have? • Not possible • 2 • 4 • 8

27. Note-taking Skills Worksheet • A. Magnetism—the properties and interactions of magnets. • 1.Interaction b/w 2 magnets, called magnetic force, increases as magnets move closer together. • 2. A magnetic field, which exerts the magnetic force, surrounds a magnet, and is closest to the magnet.

28. Note-taking(cont.) • B. Magnetic Poles—the region of a magnet where the magnetic force exerted by the magnet is strongest. • 1. All magnets have a north and a south pole. • 2. Like poles repel. Unlike poles attract. • 3. Earth has magnetic poles. • A) A compass needle is a small bar magnet that can freely rotate. • B) A compass needle always points north.

29. Note-taking(cont.) • C. Magnetic materials—iron, cobalt, and nickel • 1. The magnetic field created by each atom exerts a force on nearby atoms. • 2. Magnetic domains—groups of atoms with aligned magnetic poles. • A) In a magnet, the like poles of all the domains point in the same direction. • B) Permanent magnets are made by placing a magnetic material in a strong magnetic field, forcing a large number of magnetic domains to line up.

30. Any Questions??