1. Magnetism What makes some materials magnetic? Iron Nickel Cobalt
Where do we see magnets?

2. Magnets Compass Electromagnets at junkyards
Meters (ammeter, voltmeter)
Motors, Generators
Loudspeakers
Magnetic Tapes (sound and video)
Maglev Trains
Superconducting Magnets

3. Magnets Bar Magnets Objects attracted to ENDS (poles) NORTH SOUTH
Like poles repel, unlike poles attract

4. Comparison to Electric Charges
Magnetic poles cannot be isolated like electric positive and negative charges
If you cut a magnet in half, you will still have two poles, North and South, on each piece

5. So why are some materials magnetic?
Electrons spin on axis like a top
A change in motion of a charge produces a magnetic field (we will learn more about this later…)
Atoms have many electrons, so usually the electron spins cancel out

6. Ferromagnetic Materials
In SOME materials (Fe, Ni, Co), the fields do not cancel out completely
These are called “Ferromagnetic”

7. Magnetic Domains
Large groups of atoms whose net spins are aligned are called “magnetic domains”
10-4 to 10-1 cm across
In unmagnetised substances, the domains are random
When placed in a magnetic field, the domains get more aligned

8. Aligning Magnetic Domains
You can make a magnet out of an unmagnitized piece of iron.
Rub with magnet
Put near
big magnet

9. Types of Magnets

10. Magnetic Fields
When field lines are close together, the magnetic field is stronger

11. Using Iron Filings to See Magnetic Field

12. Strength of Magnetic Field
The symbol for magnetic field strength is B
This is a vector quantity (has magnitude and direction)
The units for B are the Gauss or Tesla
10,000 Gauss = 1 Tesla
The Earth’s magnetic field B = 1 Gauss

14. Cosmic Rays are Deflected by the Earth’s Magnetic Field

15. Aurora Borealis