HSC Physics
Module 9.3
Motors and
Generators
9.3
Motors and Generators
(30 indicative hours)
Contextual Outline
Electricity is a convenient and flexible form of energy. It can be generated and distributed with comparative ease,
and most importantly, it can be readily converted into other forms of energy such as heat, light, sound or
mechanical energy. Electricity is a key element in the development of industrialised nations.
There are many examples of electric motors both around the home: refrigerators; washing machines; vacuum
cleaners; and in the community: industrial motors and trains. The design of a motor for an electrical appliance
requires consideration of whether it will run at a set speed, how much power it must supply, whether it will be
powered by AC or DC and what reliability is required. The essentials of an electric motor are the supply of
electrical energy to a coil in a magnetic field causing it to rotate.
The generation of large quantities of electrical power requires relative motion between a magnetic field and a
coil. In the generator, mechanical energy is being converted into electrical energy while the opposite occurs in
the electric motor. Once generated, electricity must be distributed over long distances from the power station to
cities and towns. Transmission lines carry the electrical energy at a high voltage from the generator and
transformers eventually reduce the voltage to that required by the consumer.
The electricity produced by most generators is in the form of alternating current. In general AC generators,
motors and other electrical equipment are simpler, cheaper and more reliable than their DC counterparts. AC
electricity can be easily transformed into higher or lower voltages making it more versatile than DC electricity.
Since the frequency of AC electricity can be precisely controlled, it is used in motors that require accurate speed,
such as clocks and tape recorders.
Domremy – HSC Physics Module 9.3 Motors and Generators : Student Notes
Concept Map
Magnetic
Flux
Conductors
Magnetic Fields
van Allen
Radiation
belt
Force
Lenz’s Law
torque
Loudspeake
rs
The Motor
Effect
Galvanometers
DC Motors
AC Motors
Back
e.m.f
Commutator
Generators
DC Generators
Eddy
currents
AC
Generators
Transmission lines
History of
Generator
s
Social
Impact of
Technnology
Transformers
Physiological Effects
of Electrical
Generation & Supply
Electricity
Sub-stations
Motors and Generators Module Plan
Module Length: 7 weeks
Focus Area
1. Motors use
the effect of
forces on
current-carrying
conductors in
magnetic fields
Time
Concept
Resources
Humphrey’s Sets
1. discuss the effect, on the
45, 47
magnitude of the force on a
Dyett: 141-153
current-carrying conductor, of Contexts II: pp.
129-154
variations in:
– the strength of the magnetic
field in which it is located
– the magnitude of the current
in the conductor
– the length of the conductor
in the external magnetic field
– the angle between the
direction of the external
magnetic field and the
direction of the length of the
conductor
Humphrey’s Set
2. describe qualitatively and
45, 48
quantitatively the force on
Dyett: 146-153
long parallel current-carrying
conductors:
F
II
k 1 2
l
d
Practical
1. (Act 1) solve problems using
F
II
k 1 2
l
d
2. (Exp 2) perform a first-hand
investigation to demonstrate the
motor effect
3. define torque as the turning
moment of a force
using:   Fd
4. describe the forces
experienced by a currentcarrying loop in a magnetic
field and describe the net
result of the forces
5. identify that the motor
effect is due to the force
acting on a current-carrying
conductor in a magnetic field
6. describe the main features
of a DC electric motor and
the role of each feature.
7. identify that the required
magnetic fields in DC motors
can be produced either by
current-carrying coils or
permanent magnets
4. (Act 3) solve problems and
analyse information about simple
motors using   nBIAcos 
3. (Act 3) solve problems and
analyse information about the
force on current-carrying
conductors in magnetic fields
using F  BI
Contexts II: pp.
155-165
5. (Act 4) identify data sources,
gather and process information to
qualitatively describe the
application of the motor effect in:
– the galvanometer
– the loudspeaker
Domremy – HSC Physics Module 9.3 Motors and Generators : Student Notes
Focus Area
2. The relative
motion between a
conductor and
magnetic field is
used to generate
an electrical
voltage
Time
Concept
1. outline Michael Faraday‘s
discovery of the generation of
an electric current by a
moving magnet
2. define magnetic field
strength B as magnetic flux
density
3. describe the concept of
magnetic flux in terms of
magnetic flux density and
surface area
Resources
Contexts II: pp.
171-185
Humphrey’s Set
49
4 describe generated potential
difference as the rate of
change of magnetic flux
through a circuit
5 account for Lenz’s Law in
terms of conservation of
energy and relate it to the
production of back emf in
motors
6. explain that, in electric
motors, back emf opposes the
supply emf
7. explain the production of
eddy currents in terms of
Lenz’s Law.
3. Generators are
used to provide
large scale power
production.
1. identify the main
components of a generator
2. compare the structure and
function of a generator to an
electric motor
3. describe differences
between AC and DC
generators
Practical
1. (Exp 5) perform an
investigation to model the
generation of an electric current
by moving a magnet in a coil or a
coil near a magnet
2. (Exp 6) plan, chose equipment
or resources for, and perform a
first-hand investigation to predict
and verify the effect on a
generated electric current when:
- the distance between the coil and
magnet is varied
- the strength of the magnet is
varied
- the relative motion between the
coil and the magnet is varied
3. (Act 7) gather, analyse and
present information to explain
how induction is used in cooktops
in electric ranges
Contexts II: pp.
186-192
4. (Act 8) gather secondary
information to identify how eddy
currents have been utilised in
electromagnetic braking
1. (Exp 9) plan, chose equipment
or resources for, and perform a
first-hand investigation to
demonstrate the production of an
alternating current
Focus Area
4. Transformers
allow generated
power to be either
increased or
decreased before it
is used
Time
Concept
4. discuss the energy losses
that occur as energy is fed
through transmission lines
from the generator to the
consumer
Resources
5. assess the effects of the
development of AC
generators on society and the
environment
Contexts II: pp.
193-198
1. describe the purpose of
transformers in electrical
circuits
2. compare step-up and stepdown transformers
3. identify the relationship
between the ratio of the
number of turns in the
primary and secondary coils
and the ratio of primary to
secondary voltage
4. explain why current
transformations are related to
conservation of energy
5. explain the role of
transformers in electricity
sub-stations
6. discuss why some
electrical appliances in the
home that are connected to
the mains domestic power
supply use a transformer
7. discuss the impact of the
development of transformers
on society
Humphrey’s Set
50
Contexts II: pp.
199-211
Contexts II: pp.
219-244
Practical
2. (Act 10) gather and analyse
information to identify how
transmission lines are:
– insulated from supporting
structures
–protected from lightning strikes
3. (Act 11) gather secondary
information to discuss advantages
and disadvantages of AC and DC
generators and relate these to their
use
4. (Act 11) analyse secondary
information on the competition
between Westinghouse and
Edison to supply electricity to
cities.
1 (Exp 12) perform an
investigation to model the
structure of a transformer to
demonstrate how secondary
voltage is produced
2. (Act 13) solve problems and
analyse information about
transformers using:
v
n

v n
p
p
s
s
3. (Act 14) gather, analyse and
use available evidence to discuss
how difficulties of heating caused
by eddy currents in transformers
may be overcome
4. (Act 15) gather and analyse
information and use available
evidence to assess the need for
transformers in the transfer of
electrical energy from a power
station to its point of use
Domremy – HSC Physics Module 9.3 Motors and Generators : Student Notes
Focus Area
5. Motors are used
in industries and
the home usually
to convert
electrical energy
into more useful
forms of energy
Time
Concept
1. describe the main features
of an AC electric motor
Resources
Contexts II: pp.
160-164
Practical
1. (Exp 16) perform an
investigation to demonstrate the
principle of an AC induction
motor
2. (Act 17) gather, process and
analyse information to identify
some of the energy transfers and
transformations involving the
conversion of electrical energy
into more useful forms in the
home and industry
HSC Physics C2: Motors and Generators Activity 1: Force per unit length Equation
F
II
k 1 2
d
Aim: To solve problems using l
Do Humphrey’s Sets 45, 47
Do Dyett problems 141-153
HSC Physics C2: Motors and Generators Experiment 2: The Motor Effect
Aim: To perform a first-hand investigation to demonstrate the motor effect
Materials
1 X ½ inch test tube
1 bar magnet
polystyrene foam block
Bunsen burner
Power pack
1 m fine enamelled wire
4 pins
electrical leads with alligator clips
steel wool
Method
1. Wind the wire around the test tube to form a coil. Thread one end through the coil a few times to hold the coil
together:
2. Run the ends of the wire quickly through a flame and polish them with steel wool to provide a shiny surface.
3. Set up as follows:
N
To  of power pack
To  of power pack
4. The motor will work best on 4V (“B” setting) on the power pack. A setting higher than this may cause spot
welding.
N.B. A second magnet may be necessary, or at least a stronger one.
5. Give the coil slight flicks to entice it to turn.
6. Having made the motor, turn the power pack to its highest setting and observe what happens.
Discussion
1. What happens to the motor on the highest setting?
2. How can this experiment be modified to determine the conditions needed for torque.
Domremy – HSC Physics Module 9.3 Motors and Generators : Student Notes
HSC Physics C2: Motors and Generators Activity 3:Conductors & Magnetic Fields
Aim: To solve problems and analyse information about the force on current-carrying conductors in magnetic fields
using F  BI
To solve problems and analyse information about simple motors using   nBIAcos 
1. Do Humphrey’s Sets 45 and 48
2. Do Dyett problems 146-153
HSC Physics C2: Motors and Generators Activity 4: Galvanometers & Loudspeakers
Aim: identify data sources, gather and process information to qualitatively describe the application of the motor
effect in:
– the galvanometer
– the loudspeaker
Identify and describe the various parts of a galvanometer.
 Describe the different types of galvanometers.
Identify and describe the various parts of a loudspeaker.
 Describe the different types of loudspeaker.
 Evaluate the efficiency and frequency band response of each type of loudspeaker
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
HSC Physics C2: Motors and Generators Experiment 5:Generating Electric Current
Aim: To perform an investigation to model the generation of an electric current by moving a magnet in a coil or a
coil near a magnet
Materials
Bar magnet
Solenoid
Galvanometer
Major magnet
2 electrical leads
Extra wire for the solenoid.
Method
1. Connect the solenoid to the galvanometer using the leads.
2. Push the bar magnet, North pole first, slowly through the middle of the solenoid. Record the galvanometer
reading and direction.
3. Repeat step 2 quickly. Record the result.
4. Repeat step 2 slowly using the South pole first.
5. Repeat step 2 quickly using the South pole first.
6. Increase the number of turns of wire on the solenoid by winding more wire onto it.
7. Repeat steps 2 to 5 for the new solenoid.
Results
Record your results in a suitable fashion.
Discussion
1. Is a current generated when the magnet is stationary?
2. What is the relationship between the number of turns of wire in the solenoid and current generated?
3. What is the relationship between the speed of the magnet and current generated?
4. On the molecular level, what is the magnetic field doing to the electrons in the metal?
Domremy – HSC Physics Module 9.3 Motors and Generators : Student Notes
HSC Physics C2: Motors and Generators Experiment 6: Magnetism & Electric Current
Aim: To plan, chose equipment or resources for, and perform a first-hand investigation to predict and verify by
gathering and analysing information about the generated electric current when:
- the distance between the coil and magnet is varied
- the strength of the magnet is varied
- the relative motion between the coil and the magnet is varied
You must devise a method using equipment listed below and/or any other equipment you bring in.
Equipment Available
Power supplies and leads
Bar magnets
Ammeters and galvanometers
Resistor boxes
Any equipment that is reasonable (arrange with your teacher beforehand)
You should consider the following points:
 Does the experiment satisfy the aim above?
 The safety of the experiment. Any safety notes need to be explicit.
 Design your own result table. Have you repeated the experiment several times to validate the results and to
calculate a mean?
 Did you show your working?
 What are some possible sources of error? How could these errors be minimised or eliminated?
HSC Physics C2: Motors and Generators Activity 7:Electrical Induction
Aim: Gather, analyse and present information to explain how the principle of induction applies to cooktops in
electric ranges
Compare the different types of electric cooktops available – hot element, induction
 Describe how each operates
 Compare the efficiency of each.
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
HSC Physics C2: Motors and Generators Activity 8: Eddy Currents
Aim: To gather secondary information to identify how eddy currents have been utilised in electromagnetic braking
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
Domremy – HSC Physics Module 9.3 Motors and Generators : Student Notes
HSC Physics C2: Motors and Generators Experiment 9: Producing Alternating Current
Aim: To plan, chose equipment or resources for, and perform a first-hand investigation to demonstrate the
production of an alternating current
You must devise a method using equipment listed below and/or any other equipment you bring in.
Equipment Available
Power supplies and leads
magnets
soft iron core
long lengths of wire
Any equipment that is reasonable (arrange with your teacher beforehand)
You should consider the following points:
 Does the experiment satisfy the aim above?
 The safety of the experiment. Any safety notes need to be explicit.
 Design your own result table. Have you repeated the experiment several times to validate the results and to
calculate a mean?
 Did you show your working?
 What are some possible sources of error? How could these errors be minimised or eliminated?
HSC Physics C2: Motors and Generators Activity 10: Transmission Lines
Aim: To gather and analyse information to identify how transmission lines are:
– insulated from supporting structures
–protected from lightning strikes
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
HSC Physics C2: Motors and Generators Activity 11: AC vs DC – Westinghouse vs Edison
Aim: 1. To gather secondary information to compare advantages and disadvantages of AC and DC generators and
relate these to their use in industry.
2. analyse secondary information on the competition between Westinghouse and Edison to supply electricity
to cities.
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
Domremy – HSC Physics Module 9.3 Motors and Generators : Student Notes
HSC Physics C2: Motors and Generators Experiment 12: Transformers
Aim: To model the structure of a transformer to demonstrate how secondary voltage is produced.
Materials
Soft iron bar
Two sets of long wire
Resistor box
Power supply and leads
AC voltmeter
AC ammeter
Method
1. Set up the equipment as shown in the diagram below:
Power supply
6V AC
V
wire
50 resistor
Soft iron core
20 resistor
Primary circuit Secondary circuit
2. Measure the voltage produced by the power supply and the secondary circuit.
3. Measure the current produced by the power supply and the secondary circuit.
4. Remove the soft iron core, intertwine the two coils together, and repeat steps 2 and 3.
Discussion
1. What is the purpose of the soft iron core?
2. What is the relationship between the voltage and current in the primary and secondary circuits?
3. Why are the resistors used in the primary and secondary circuits?
HSC Physics C2: Motors and Generators Activity 13: Transformers II
Aim: To solve problems and analyse information about transformers using
vp
vs

np
ns

Is
Ip
1. Do Humphrey’s Set 50
2. Cross country cables transmit voltages at 330,000 V AC at currents of 100A. What current is available when
this transmission is stepped down to 10,000 V? What is the winding ratio for such a transformer?
HSC Physics C2: Motors and Generators Activity 14: Heating in Transformers
Aim: To gather, analyse and use available evidence to discuss how difficulties of heating caused by eddy currents in
transformers may be overcome
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
HSC Physics C2: Motors and Generators Activity 15: Electrical Transmission
Aim: To gather and analyse information and use available evidence to assess the need for transformers in the transfer
of electrical energy from a power station to its point of use.
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
Domremy – HSC Physics Module 9.3 Motors and Generators : Student Notes
HSC Physics C2: Motors and Generators Experiment 16: AC Induction Motors
Aim: To perform an investigation to demonstrate the principle of an AC induction motor
Materials
Power tool that uses an AC induction motor.
Tools to disassemble the power tool
Method
The power tool is taken apart and examined.
Discussion
1. How is an AC induction motor different to other motors?
2. Why are the majority of motors AC induction type?
HSC Physics C2: Motors and Generators Activity 17: AC Induction Motors II
Aim: To gather, process and analyse information to identify some of the energy transfers and transformations
involving the conversion of electrical energy into more useful forms in the home and industry
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.