Magnetism

1
Chapter 18

• Magnetism

2
Section 18.1

• Magnets and Magnetic Fields

3
Lodestone

• Naturally occurring magnetic rock found in Greece
  3000 years ago.

4
Lodestone composed of magnetite.
5

• Lodestone is a permanent magnet (magnetic all the
  time).
• Some substances can be magnetized permanently.
• Iron nail can be magnetized by stroking it
  several times with a permanent magnet.

6
(No Transcript)
7
Magnetically hard

• Difficult to magnetize, but once magnetized,
  dont lose their magnetism easily.
• Examples cobalt and nickel.

8
Cobalt and nickel
9
Magnetic Force

• The forces magnets exert on each other.

10
(No Transcript)
11
Magnetic pole

• An area of a magnet where the magnetic force
  appears to be the strongest.

12
Like poles repel
13
Opposite poles attract
14
Magnetic Field

• A region where a magnetic force can be detected.

15
(No Transcript)
16
North pole of compass points towards the south of
the magnet
17
Compass

• A magnet suspended on top of a pivot so that the
  magnet can rotate freely.

18
(No Transcript)
19
Earth is like a giant bar magnet.
20

• Earths magnetic poles are not the same as its
  geographic poles.

21
Section 18.2

• Magnetism and Electric Currents.

22

• Electric currents produce magnetic fields.

23
(No Transcript)
24
(No Transcript)
25

• The magnetic field of a coil of wire resembles
  that of a bar magnet.

26
Bar magnet and solenoid
27
Solenoid

• A long, wound coil of insulated wire.

28
Strength of a solenoid depends on

• Number of loops in the wire.
• Amount of current in the wire.

29

• More loops and more current produces a stronger
  magnetic field.

30
Electromagnet

• A strong magnet created when an iron core is
  inserted into the center of a current-carrying
  solenoid.

31
Electromagnet
32

• Magnetism is caused by moving charges
  (electrons).
• Electron spin produces tiny magnetic fields.

33

• Magnetic fields around electrons can cancel each
  othermaterial not magnetic.
• In iron, nickel, and cobalt the magnetic fields
  of the electrons dont cancel each othermagnets.
  

34
Domain

• A microscopic magnetic region composed of a group
  of atoms whose magnetic fields are aligned in a
  common direction.

35
(No Transcript)
36
Electromagnetic Devices

• Galvanometer.
• Electric motor.

37
Galvanometer

• An instrument that measures the amount of current
  in a circuit.

38
(No Transcript)
39

• A Galvanometer consists of a coil of insulated
  wire wrapped around an iron core that can spin
  between the poles of a permanent magnet.

40
(No Transcript)
41
Electric Motor

• A device that converts electrical energy to
  mechanical energy.

42
(No Transcript)
43

• In an electric motor, the current in the coil
  produces a magnetic field that interacts with the
  magnetic field of the surrounding magnet, causing
  the coil to turn.

44

• The coil of wire keeps spinning in an electric
  motor. If the coil is attached to a shaft, it
  can do work.
• Used in mechanical toys.

45
(No Transcript)
46
(No Transcript)
47

• Stereo speakers use magnetic force to produce
  sound.

48
Section 18.3

• Electric Current from Magnetism.

49

• In 1831, Michael Faraday discovered that an
  electric current can be produced by pushing a
  magnet through a coil of wire.

50
(No Transcript)
51
Electromagnetic induction

• The production of a current in a conducting
  circuit by the change in the strength, position,
  or orientation of an external magnetic field.

52
Faradays Law

• An electric current can be produced in a circuit
  by a changing magnetic field.

53
Generator

• A device that uses electromagnetic induction to
  convert mechanical energy to electrical energy.

54
(No Transcript)
55
Mechanical energy to electrical energy.
56
Alternating current

• An electric current that changes direction at
  regular intervals also called AC generator.
• Used at home

57

• Power plants use generators to convert mechanical
  energy to electrical energy.

58
Sources of the mechanical energy for power plants

• Dams.
• Coal.
• Nuclear fission.
• Wind.
• Geothermal.
• Solar power.

59
(No Transcript)
60

• Electricity and magnetism are two aspects of a
  single electromagnetic force.

61
(No Transcript)
62
Transformer

• A device that can change one alternating-current
  voltage to a different alternating-current
  voltage.

63

• Transformers can increase or decrease voltage.

64

• In a transformer, the magnetic field produced by
  a primary coil induces a current in a secondary
  coil.

65

• The voltage across the secondary coil of a
  transformer is proportional to the number of
  loops or turns it has relative to the number of
  turns in the primary coil.

66
(No Transcript)
67
(No Transcript)
68
(No Transcript)
69
(No Transcript)
70
(No Transcript)