1. Chapter 8 Magnetism and Its Uses
Section 1 Magnetism

2. Magnetism
This refers to the properties and the interactions of magnets

3. Magnets First found by the Greeks nearly 3,000 years ago
Lodestone- naturally occurring magnetic rocks

4. Magnets Lodestone contains magnetite Magnetite- iron based material
First found in Magnesia
- hence the name “magnetism”

5. Magnetic Force This as the magnets move closer together
and as the magnets move farther apart

6. Magnetic Field Exerts a force on other magnetic objects
Strongest close to magnet
Weaker farther away from magnet
p. 225 Fig. 1

7. Magnetic Poles All magnets have a north and south pole
What happens when you break a bar magnet in half?

8. Destroying a magnet There are only two ways to destroy a magnet:
Heat it up
Hit it REALLY hard

9. Magnetic Attraction
North and North or South and South poles REPEL each other
North and South poles ATTRACT each other

10. Magnetic Materials Not all metal objects are attracted to a magnet
Only those made of materials found in the Iron Triad:
Iron, Cobalt, or Nickel

11. Chapter 8 Magnetism and Its Uses
Section 2 Electricity and Magnetism

12. Electric Current and Magnetism
Relationship discovered by Hans Christian Oersted, Danish physics teacher
Noticed that flow of electric current affected direction of compass needle

13. Hypothesized that electric current creates magnetic field
He was correct

14. Look at Figure 8 p. 231
As the direction of the current reverses so does the magnetic field
When the current so does the strength of the magnetic field

15. Electromagnets A temporary magnet
Made by wrapping wire around iron core and adding electric current

16. Magnetic field is stronger in looped wire than straight wire
More loops = stronger magnetic field

17. Solenoid- is a single wire wrapped into a cylindrical wire coil
If you have a solenoid wrapped around an iron core you form an electromagnet

18. Properties of Electromagnets
Temporary magnets
The strength of the magnetic field can be increased or decreased depending on the # of loops around the iron core

19. Electromagnets attract magnetic materials and are attracted or repelled by other magnets.
They are useful because their magnetic properties can be controlled by changing the current

20. Electromagnets are used in things like stereo speakers (where they convert electrical energy into mechanical energy to produce sound) and electric motors
Fig. 10 p. 233

21. Electromagnets When the ends are connected:
1. Electrons flow as quickly as possible from the – to the + end of the battery
2. Battery will drain quickly ( there is no load in the middle of the wire)
3.Small magnetic field is produced in the wire

22. Electromagnetic Devices
Galvanometer- devices that use electromagnet to measure electric current
Examples: Gauges in your car
Electric Motor- a device that converts electrical energy into mechanical energy

23. Electric Motor Contains an electromagnet
The magnetic field flips at the right moment which causes the electric motor to spin freely

24. Chapter 8 Magnetism and Its Uses
Section 3 Producing Electric Current

25. Moving a loop of wire through magnetic field produces electric current
Found by Michael Faraday & Joseph Henry
- 1831

26. Magnet and wire must move relative to each other
Causes magnetic field in wire to change over time

27. That change can induce current in nearby wire
Called electromagnetic induction

28. Generators Uses electromagnetic induction Transforms
Mech. Energy  Electrical Energy

29. Mech. Energy
From turning handle
This rotates coil of wire between poles of permanent magnet.

30. Each time end of coil pass poles of permanent magnet the current changes direction.
It will change direction twice

31. Electric Generators Used in cars, and is called an “alternator”
Provides electrical energy to operate lights and other accessories

32. Electricity in Your Home
Comes from power plants with huge generators
These generators have many a lot of wire wrapped around huge iron cores.

33. Attached to turbine
When fossil fuels burn  heats water  steam pushes turbine blades
Used as mech. energy

34. That mechanical energy turns wire coil
Produces electrical energy

35. Turbines use:
Wind
Water
Steam
to turn the blades.

36. Direct Current “DC” Current flows only in one direction
Produced in a battery

37. Alternating Current “AC”
This reverses the direction of the current in a regular pattern
Ex: Generator produces AC
Wall outlets

38. Current produced by power plants transmitted along power lines
Some current lost as heat
Longer the wire, the more current is lost

39. Reduce Current Loss
Transmit current at high voltage
150,000 volts

40. Transformer Voltage cannot enter home @ 150,000 volts
Must be decreased
Use transformer

41. Transformer
Used to increase or decrease voltage in AC

42. Parts of Transformer Primary Coil (comes first)
Secondary Coil (comes second)
Iron Core

43. Input vs. Output Voltage
Input goes through primary coil
Output produced from secondary coil

44. Step-Up Transformer Increases voltage
Secondary coil has more loops than primary coil

45. Twice as many secondary loops = twice as much output voltage

46. Step-Down Transformer
Decreases voltage
Secondary coil has less loops than primary coil

47. Half as many secondary loops = half as much voltage

48. Transmitting Alternating Current
Step-up transformer used when current leaves power plant
Travels through wires
Goes through step- down transformer
Enters home