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KICKSTART PHYSICS
The University of Sydney
School of Physics
Motors and Generators
MOTORS AND GENERATORS
SCHOOL OF
PHYSICS
1.
THE MOTOR EFFECT
2.
LENZ’S LAW
3.
GENERATORS
4.
TRANSFORMERS
5.
AC INDUCTION MOTORS
Kickstart would like to acknowledge and pay respect to the traditional owners of the land– the Gadigal people of the Eora Nation. It
is upon their ancestral lands that the University of Sydney is built. As we share our own knowledge, teaching, learning, and research
practices within this University may we also pay respect to the knowledge embedded forever within the Aboriginal Custodianship of
For more information head to
http://sydney.edu.au/science/physics/schools_community/kickstart.shtml
The University of Sydney
School of Physics
Motors and Generators
Generate some motor-vation
List three risks in the 2nd year lab
Risk
Electricity
Radiation
Equipment
Water
LN2
Consequence
Electrocution
Radiation sickness
Injury
Slip/injury
Frostbite
Precaution
Safety Switch
Low dose, shielding
Don’t touch
No food drink in lab
PPE
Careers with Motors and Generators
Your demonstrator might be able to help with this.
What sort of career do you think you could get if you studied this topic at the University of Sydney?
Industry
Research
•
Finance/Tech companies
•
University
•
Gaming
•
Any research field
•
Solar/energy
•
•
Veritasium
Public service
•
CSIRO, DSTO, NMI,
Geoscience, Questacon
•
Government
•
Teachers
The University of Sydney
School of Physics
Motors and Generators
The Motor Effect
An electric charge experiences a force when it moves in a magnetic field. Thus,
a current-carrying conductor feels a force from a magnetic field. This is the
motor effect.
Label the parts of the motor on the pictures below. Are these DC motors or
AC? Or both? How can you tell?
Rotor
Stator
Power source
Brushes
Commutator
Describe the application of the motor effect in the galvanometer and the
loudspeaker
Galvanometer
Loudspeaker
Features:
- Permanent Magnet
- Coil
- Spring
- Power source
Features:
- Permanent Magnet
- Coil
- Diaphragm
- Power source
Characteristics:
- Current in wire moves in magnetic
field
- Spring resists motion of coil
- When force from spring is equal to
force from motor, needle is still
- Depending on resistance of circuit,
different scale is read
Characteristics:
- Current in wire moves in magnetic field up or
down
- Wire connected to diaphragm
- Depending on current, different sounds are
produced
The University of Sydney
School of Physics
Motors and Generators
Electromagnetic Induction and Lenz’s Law
Lenz’s Law
There are 5 parts to Lenz’s Law.
A changing Magnetic flux generates an electro-motive force which induces a
current that produces its own magnetic field that opposes the original change
that caused it.
Predict
Observe
Apply
Magnet and
coil
Student makes their own
predictions
Student makes their own
observations
Electricity generation
Falling
magnet
Student makes their own
predictions
Student makes their own
observations
Magnetic dampening
Jumping
rings
Student makes their own
predictions
Student makes their own
observations
Projectiles, launching
Pendulum
Student makes their own
predictions
Student makes their own
observations
Magnetic braking
Arago’s disk
Student makes their own
predictions
Student makes their own
observations
Induction motor
The University of Sydney
School of Physics
Motors and Generators
Generators
AC/DC Generator
How can you tell if the
generator is producing AC
or DC electricity? Draw
the output of the generator
as viewed on the DSO
Draw what you think the
output of the generator
would look like on the
DSO:
The University of Sydney
School of Physics
Motors and Generators
Transformers
Transformers use the ideas of
electromagnetic induction to
transform one voltage into another.
We can use experimentation to
determine the relationship between
the voltage and the number of turns
in the coil.
First we can count the number of
turns in the coil, then use the
multimetre to measure the voltage.
What is the best way to represent
this data?
Volts, Vs (V)
Number of coils, Ns
~0.4
1
~0.9
2
~1.5
4
~2.3
6
~3.2
8
Conclusion:
From this graph, what can you say about the relationship between the voltage
and number of turns in the secondary coil?
- direct positive relationship
How would you represent this mathematically? Hint, it’s a straight line.
- 𝑦 = 𝑚𝑥 + 𝑏
Discussion:
You have the relationship between the secondary voltage and coils, Calculate
the relationship between the primary voltage and coils?
𝑉!
3.2
= = 0.4 𝑛!
8
Are they the same? Can you write a general expression for all of these 4 terms?
𝑉!
𝑉!
= 𝑛!
𝑛!
The University of Sydney
School of Physics
Motors and Generators
AC Induction Motors
Construct from the parts provided,
a model AC induction motor.
Write down your method for the construction of the models
- collect 3 blue iron bars
- collect 3 yellow coils
- place iron into centre of coils
- place coils and iron onto triangular base
- place squirrel cage onto support in middle of base
- collect 4 radial iron parts
- collect 4 black coils
- place iron inside coils
- place coils onto dowel on blue base
- place large circular squirrel cage in centre
Calculate the Synchronous speed:
𝑛! =
!"#×!
! =
where 𝑓 is the motor
supply's frequency in
hertz and 𝑝 is the
number of magnetic
poles.
Draw the output of the 2
phases on the Digital
Signal Oscilloscope at
90 out of phase
The University of Sydney
School of Physics
Motors and Generators
Title: Voltage Vs # of coils