1. Unit 11
Magnetism

2. Magnets magnetism – force of attraction or repulsion
not all objects are affected by the force of magnetism
ex. wood, glass, paper, plastic
common metals affected by magnetism are iron, nickel, and cobalt

3. Magnets poles – two ends of a magnet every magnet has two poles
north (N) pole
south (S) pole
even if you break a magnet in half, each half will have a north pole and a south pole

4. Magnets the north pole of a magnet points North
it is often called “North-seeking”

5. Properties of Magnets
if a north pole and a south pole are brought together, they will attract each other
opposites attract

6. Properties of Magnets
if the north pole of one magnet is brought near the north pole of another magnet, they will repel each other
if two south poles are brought together, they will repel each other

7. Properties of Magnets like magnetic poles repel each other
unlike magnetic poles attract each other

8. Magnetic Fields
magnetic field – area around a magnet where magnetic forces can act
a magnetic field is made up of magnetic lines of force

9. Magnetic Fields
magnetic lines of force – lines that show the shape of a magnetic field
the magnetic lines of force are closest together at the poles of the magnet
this is where the magnet is strongest

10. Making a Magnet some magnets occur in nature
these magnets are called natural magnets
ex. magnetite (also called lodestone)

11. Making a Magnet
materials that are not natural magnets can be magnetized

12. Making a Magnet
magnetic induction – process by which a material can be made into a magnet

13. Making a Magnet
some materials are easy to magnetize
ex. iron

14. Making a Magnet
a material that is easily magnetized tends to lose its magnetism quickly
a magnet made of this kind of material is called a temporary magnet

15. Making a Magnet
materials that are hard to magnetize will also stay magnetized for a long time
a magnet that is hard to magnetize but tends to keep its magnetism is called a permanent magnet

16. The Earth as a Magnet William Gilbert a British scientist
the Earth has north and south poles like a bar magnet

17. The Earth as a Magnet
the Earth has a North Magnetic Pole and a South Magnetic Pole
the North Magnetic Pole is located near the geographic North Pole
the South Magnetic Pole is located near the geographic South Pole

18. The Earth as a Magnet
the North Magnetic Pole is like the south pole of a bar magnet
the South Magnetic Pole is like the north pole of a bar magnet

19. The Earth as a Magnet
the Earth is surrounded by a magnetic field which extends far into space
magnetosphere – region of the Earth’s magnetic field

20. The Earth as a Magnet
the magnetosphere traps charged particles from the sun
when these particles enter the atmosphere, an aurora is formed
auroras are also called the northern and southern lights

21. Electricity and Magnetism
Hans Oersted
about 200 years ago
an electric current flowing in a wire causes a compass needle to move

22. Electricity and Magnetism
an electric current passing through a wire causes a magnetic field

23. Electricity and Magnetism
electromagnetism – relationship between electricity and magnetism

24. Electricity and Magnetism
Michael Faraday (British scientist)
Joseph Henry (American scientist)
when a wire is moved across a magnetic field, an electric current is induced in the wire

25. Electricity and Magnetism
electromagnetic induction – process by which an electric current is produced by moving a wire in a magnetic field

26. Electricity and Magnetism
a wire carrying an electric current always has a magnetic field around it
the magnetic field in a straight wire is not very strong
if the wire is wound into a coil, the magnetic field becomes much stronger as the individual magnetic fields overlap
the greater the number of coils, the stronger the magnetic field

27. Electromagnets
electromagnet – temporary magnet made by wrapping a current-carrying wire around an iron core
the center of an electromagnet is called the core
it is often made of iron

28. Electromagnets
as long as current is flowing, an electromagnet has a magnetic field
when current is turned off, there is no longer a magnetic field

29. Electromagnets there are two ways to make an electromagnet stronger
increasing the number of coils
increasing the amount of current

30. Electromagnets
electromagnets are useful because they can be turned on and off
electromagnets have many important uses
ex. radios, telephones, computers

31. Electromagnets
changing the direction of an electric current causes the poles of an electromagnet to reverse
this feature is important in the production of electric motors

32. Transformers
transformer – device in which alternating current in one coil of wire induces a current in a second coil

33. Transformers
a transformer consists of two coils of wire around a magnet
the first coil, called the primary coil, is connected to the power source
the second coil, called the secondary coil, is connected to the load
a load is something that uses electricity, such as a light bulb or a motor

34. Transformers
a transformer only works with alternating current

35. Transformers a step-up transformer increases voltage
it consists of more coils of wire in the secondary coil than the primary coil

36. Transformers a step-down transformer decreases voltage
it consists of more coils of wire in the primary coil than the secondary coil

37. Electric Motors
electric motor – device that changes electrical energy into mechanical energy

38. Electric Motors
an electric motor is made up of an electromagnet and a permanent magnet

39. Electric Motors
the electromagnet is free to turn and is hooked up to a source of alternating current
changing the direction of an electric current causes the poles of an electromagnet to reverse

40. Electric Motors
attraction and repulsion between the electromagnet and the permanent magnet cause the electromagnet to spin

41. Electric Motors
an electric motor can use direct current if a special switch is used

42. Generators
generator – device that changes mechanical energy into electrical energy
a current can be induced in a loop of wire by spinning the loop inside a magnetic field
due to the changing direction of the wire, an alternating current is produced

43. Generators
an electric generator is made up of an insulated loop of wire and a U-shaped magnet
spinning the loop of wire in the magnetic field of the magnet produces an electric current

44. Generators
most of the energy we use every day comes from generators

45. Generators
mechanical energy for many generators is supplied by turbines
a turbine is a large wheel that is turned by moving steam or water