Lesson IV “Magnets & Magnetic Fields”

1. Lesson IV “Magnets & Magnetic Fields” Matter & Energy

2. S.W.B.A.T. • Identify the effects of magnetic forces and how magnetic poles interact • Describe magnetic field lines around a magnet • Explain how & why materials become magnetized

3. Magnetic Forces • Ancient cultures recognized that some rocks contained “mysterious” particles that attracted iron • The word “magnet” originates from the ancient Greek city of Magnesia

4. Magnetic Forces • Magnesia contained mineral deposits later called magnetite or lodestone • The Chinese were the first to use magnetite to eventually make a compass needle for navigation

5. Magnetic Forces • Magnetic force is an area of influence that attracts or repels other magnets, iron and other metals, or electric charges • Magnetic force strength decreases with distance like the electric force

6. Magnetic Forces • Magnetic poles include a “north” and “south” point at the end of the magnet • Opposite poles (N)(S) attract • Like poles (N)(N) & (S)(S) repel

7. Like Poles Repel – Unlike Poles Attract

8. Magnetic Forces • A magnetic field describes the area around the poles • Lines are used showing field direction and strength as measured by a compass

9. Magnetic Forces • Magnetic field lines start from the north and are strongest at the poles • Iron filings can also be used to “map out” magnetic field lines • Iron filings show where magnetic forces are strongest & weakest

10. Magnetic Forces • Earth’s magnetosphere is generated from the iron core rotating slightly faster than the mantle • The magnetic field extends (on average) about ½ way to the Moon and protects Earth from harmful cosmic radiation

11. Magnetic Forces • Geographic north is located 90 degrees north of the equator • Magnetic north is located about 81 degrees north of the equator • Earth’s magnetic field “wanders” or moves due to changes in iron core currents and mantle interactions

13. Video (1:58) “Magnetic North Pole Moves to Siberia”

14. Magnetic Forces • Magnetic north is actually magnetic south- since the north tip of a magnet is attracted to it and opposites attract! • Magnetic poles on Earth have switched places many times in the past

15. Magnetic Materials • Atoms have electrons that “spin” – which gives the electrons magnetic properties • “Paired” electrons spin opposite to each other which cancels out their magnetic properties

16. Magnetic Materials • Unpaired electrons in metals such as iron, nickel & cobalt can form a strong magnetic field • Magnetic domainrefers to a region with a very large number of unpaired electrons

17. Magnetic Materials • Ferromagnetic metals like iron can become magnetized only because of its magnetic domains • Ferromagnetic materials can be temporarily magnetized if placed in a magnetic field • The magnetic domains “line up” or align to create a temporary magnet

18. Magnetic Materials • Temporary magnets quickly lose their magnetism after leaving a magnetic field • A permanentmagnet holds on to its magnetic properties after leaving a magnetic field

19. Magnetic Materials • Cutting amagnet in half will create two separate magnets, each with a north & south pole • A magnet cannot have just one pole – no matter how many times you cut it in half!

20. Magnetic Materials • Super magnets are the strongest type of permanent magnets • Super magnets are used in many applications such as MRI’s and particle accelerators Video (3:32) “Largest Neodymium Magnet in the World?”

21. Class Activity • A magnet is placed on a refrigerator door to hold up your A+ assignment given in science class • Explain which material is the permanent magnet and which is the temporary magnet and why