Download Section 17.3 - CPO Science

UNIT FIVE: Electricity and Magnetism
 Chapter 16 Electricity
 Chapter 17 Magnetism
Chapter Seventeen: Magnetism
 17.1 Properties of Magnets
 17.2 Electromagnets
 17.3 Electric Motors and Generators
 17.4 Generating Electricity
Chapter 17.3 Learning Goals
 Describe the role of electromagnetism in
the function of electric motors and
generators.
 Contrast energy transformations in
electric motors and generators.
 Explain the principle of electromagnetic
induction.
17.3 Electric motors and generators
 Permanent magnets and electromagnets
work together to make electric motors
and generators.
 The secret is in the ability of an
electromagnet to reverse its north and
south poles.
17.3 Electric motors
 Around the edge of
a disk are several
magnets, their
alternating north
and south poles
facing out.
17.3 Electric motors
 To make the disk
spin, you bring a
permanent magnet
close to its edge.
 The free magnet
attracts one of the
magnets in the disk
and repels the next
one.
The disk is a “rotor”
because it rotates.
17.3 Electric motors
 In a working electric
motor, an electromagnet
replaces the magnet you
reversed with your
fingers.
 The electromagnet
switches its poles to
make the rotor keep
turning.
17.3 Electric motors
 As the rotor spins, a
commutator reverses
the direction of the
current in the
electromagnet.
17.3 Electric motors
Motors have three parts:
1. A rotor with magnets that
alternate.
2. One or more fixed
magnets around the rotor.
3. A commutator that
switches the direction of
current to keep the rotor
spinning.
17.3 Battery run electric motors
 An electric motor that runs from batteries
has the same three parts.
 The permanent magnets are on the
outside, and the electromagnets turn in
the rotor.
17.3 Battery run electric motors
 A simple battery
powered motor
has three
electromagnets in
the armature.
17.3 Electromagnetic induction
 Motors transform electrical energy into
mechanical energy.
 Electric generators do the opposite.
 They transform mechanical energy into
electrical energy.
 The process of using a moving magnet to
create electric current is called
electromagnetic induction.
17.3 Electromagnetic induction
 A moving magnet produces a current in
a coil of wire.
17.3 Generating electricity
 A generator converts mechanical energy
into electrical energy using the law of
induction.
 As long as the disk is spinning, there is a
changing magnetic field through the coil and
electric current is created.
Investigation 17C
Electromagnetic Forces
 Key Question:
How does an electric motor work?