MOTORS AND
GENERATORS
HSC KICKSTART PHYSICS
WORKSHOP
LIST OF EXPERIMENTS
1. The Motor Effect
2. Electromagnetic Induction and
Lenz’s Law
3. Generators
4. Transformers
5. AC Induction Motors
Name:_____________________________
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 Country.
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.
B field into
page
force
path of positively charged particle
velocity
A Working Motor
Label the parts of the motor on the pictures below.
Are these DC motors or AC? Or both? How can you tell?
The University of Sydney
School of Physics
Motors and Generators
Galvanometer
Features:
Characteristics:
Describe the application of the motor effect in a galvanometer.
Loudspeaker
Features:
Characteristics:
Describe the application of the motor effect in a loudspeaker.
The University of Sydney
School of Physics
Motors and Generators
Electromagnetic Induction and Lenz’s Law
Using the Predict, Observe, Explain model of scientific enquiry, examine these 5
experiments to synthesise the information into a description of Lenz’s Law.
Magnet and coil
The wire coil is connected to a galvanometer that measures small amounts of current.
Move the magnet near the coil and notice the current induced.
What happens when you move the magnet faster? What happens when you use the
weaker (smaller) magnet?
When you bring the magnet’s north pole towards the coil, can you tell which way the
induced current flows in the coil? How? Explain using a diagram.
Predict
Observe
Explain
The University of Sydney
School of Physics
Motors and Generators
Falling magnets
You have a very strong magnet — a neodymium magnet — and some tubes. Drop the
magnet down the tubes and observe how long it takes for the magnet to reach the
bottom of each tube.
The magnet falls slower in the copper tube than in the PVC pipe. Why?
Predict
Observe
Explain
Jumping rings
Why do the rings jump into the air? Which ones don’t work and why?
Predict
Observe
Explain
The University of Sydney
School of Physics
Motors and Generators
Pendulum
Three different pendulums can be swung between the poles of the permanent magnet.
Try each one in turn and observe how long they swing before stopping. Where is the
stopping force coming from? How can this be used in electromagnetic braking?
Predict
Observe
Explain
Arago’s Disk
Turn the magnets past the disk. The disk will move too. What is the disk made of? Is it
magnetic? Why does the disk spin? (This phenomenon is used in AC induction motors).
Predict
Observe
Explain
Lenz’s Law
There are 4 parts to Lenz’s Law.
1. A __________________________________________ induces a
2. ____________________________________________ that produces an
3. ____________________________________________ force that
4. ____________________________________________ the original force.
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 CRO screen for both AC and DC
V
t
V
t
The University of Sydney
School of Physics
Motors and Generators
Twelve-phase generator
What kind of commutator does the twelve-phase generator have?
Predict and draw what you think the output of the generator would look like on the CRO:
V
t
The University of Sydney
School of Physics
Motors and Generators
Transformers
Risk Analysis
A very important part of any experimentation in physics is the identification of any risks,
and the subsequent mitigation of those risks. As you can imagine, scientists use some
very cool, and technical pieces of apparatus and equipment. High voltage falls into this
category.
Before we begin, identify three risks associated
with high voltage. Once these risks have been
identified, you must identify what might happen if
the risks were to eventuate, and of course, what
we can do to mitigate against the risks. These
would be our safety rules.
Assign a number to each of your risks using the
table to the left.
Risk
Consequence
Precaution
Transformers use the ideas of electromagnetic induction to transform one voltage into
another. The number of turns in the primary and secondary coils is the crucial point
here, since the ratio of the primary voltage to the secondary voltage is
Vp/Vs = np/ns
That is, if the number of turns in the secondary coil is increased, the voltage output of
the secondary coil is increased.
The University of Sydney
School of Physics
Motors and Generators
DIY transformer
Primary
np = ____________
Secondary
ns = ____________
Vp = ____________
So we should get Vs = ____________
Compare your prediction to the actual value by using a multimeter:
Vs =
Does the predicted value match the measured value?
What reasons can you give as to why our measurement might be different to the
calculated value?
Explain how this effect is used for transmission of electricity from power stations t our
homes.
Cause:
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Relationship between
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Why/How
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Effect:
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The University of Sydney
School of Physics
Motors and Generators
AC Induction Motors
The parts of the squirrel-cage rotor are:
Constuct from the parts provided, a
working AC induction motor.
Different types of motors
Different types of motors have different
components. Fill in the table below for each type of motor.
Component
Rotor
Stator
Commutator
Power supply
Physics concept
behind motor
Applications/
Examples
DC motor
Description
Universal Motor
AC Induction
motor
The University of Sydney
School of Physics
Motors and Generators
Generate some motor-vation
If you listen closely throughout the workshop, the demonstrators might let some of this
info slip, but if not, just ask them.
What does your demonstrator do here at the School of Physics?
or random fact from your demonstrator
Can you list some safety measures in the lab?
Find and list the 4 famous scientists in the lab.
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
Public service
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The University of Sydney
School of Physics
Motors and Generators
Physics Kickstart 2012
student survey
School Name_____________________
Demonstrator’s name________________
1 (a) Have you done this topic in class already?
Yes
No
1 (b) What did you learn from the workshops that you couldn’t get from your class?
2 (a) Why did you choose HSC Physics?
2 (b) How do you think Kickstart will help with your HSC?
2 (c) How has Kickstart influenced your ideas about physics?
2 (d) Are you now more likely to do Physics at the University of Sydney?
No
3 (a) How would you rate Kickstart Physics overall? ________
out of 10
3 (b) What part of the workshop made most sense to you?
3 (c) Any other comments, like how could the workshops be improved?
Yes