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Turn the Crank
Robert Friedman, Nick Halmagyi, Walter Glogowski Chris Kelso, & Reid
Sherman
Student paragraph
In this lab you will construct your own device which converts electrical energy into
mechanical energy: a simple DC motor. In this process you will learn all the basic
principles that go into designing any type of motor. We will then turn the tables
and you will investigate two methods that utilize a process called electromagnetic
induction, where mechanical energy is converted into electrical energy. Tying in
with the sustainability theme, both these methods will be pollution free. In the first
method, you are going to use your awesome leg power to generate electricity by
cycling a bike. Then we are going to divide up into teams of two and build a
windmill. The wind will turn the blades on the windmill and then this kinetic energy
is again going to be converted into electricity.
Objectives
- Learn simple circuit vocabulary (voltage, current, EMF, power, resistance)
- Understand that electrical energy can be converted into mechanical energy by
observing a direct example
- Construct a simple DC motor
- Understand that mechanical energy can be converted into electrical energy by
observing direct examples
- Understand that a rotating coil in a magnetic field produces EMF/current
- Use a simple motor as a generator by spinning the rotor by hand.
- Compute instantaneous power for an electrical component given current and
voltage
- Innovate a standard windmill design to produce the highest output windmill.
- Understand the process of trial and error that is necessary for innovation in
science and engineering.
Background
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Circuit terminology
current- the number of electrons that flow past a certain point in a wire per unit
time
voltage – a change in voltage is what causes a current to flow in a material.
Electrons will flow from a region of lower voltage to a region of higher voltage.
conductor – a material that can easily support a current. Metals are typically good
conductors because they have many free electrons
resistance - a quanitative measure of the conductance of a material, a good
conductor has a small resistance
insulator – a material that does not easily support a current
electromotive force (EMF) - this is the term used to describe the action of a
battery. A battery causes electrons to flow from higher voltage to lower voltage,
opposite to their normal flow. This requires an energy input into the system, which
is typically provided by a chemical reaction.
A simple model can be useful in understanding the relationships between circuit
elements. In this model, the electrons flowing in a wire are represented by
students (the electrons) going down a slide (the wire). The number of students
that pass a given point will be the current. The height of the slide represents the
voltage change. The higher the slide, the faster the students will move, producing
a larger current. How smooth the slide is represents the resistance of the wire.
For a given height of slide, the smoother it is the faster the students will go. This is
like saying that for a given voltage, the lower the resistance of a wire, the more
current it will produce. The final part of the picture is the escalator, which is
representing a battery in our model. The escalator takes students from the bottom
of the hill back to the top. The escalator is utilizing energy to move the students in
the direction opposite to their normal flow. In our model, this is like saying that
the EMF of the battery causes the electrons to flow from higher voltage to lower
voltage, opposite to their normal flow.
Question
Draw a picture of this circuit model in your lab notebook. Be sure to label each
part with the electrical component that it is supposed to represent.
Magnetism
Almost everyone is familiar with the phenomena of magnetism. Certain materials
can become magnetic (or magnetized) and then can attract or repel other
magnetic materials. Every magnet has a north pole and a south pole. Like poles
repel and unlike poles attract. These forces can be exerted even though
the objects are not in contact. One way to describe this process is to introduce the
concept of the magnetic field. This magnetic field will point from the north pole of
a magnet towards its south pole. This magnetic field helps to describe the region
of space over which a magnet can exert forces. The magnetic field can be
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visualized by placing many small iron filings (which are magnetic) near a magnet.
A picture of this is shown below.
source http://www.starpulls.com/magnet.gif
Question
For the three cases shown below, decide if the magnets will attract or repel.
Electromagnets
Another way to create a magnetic field is to run a current through a bunch of loops
of wire. This object is called an electromagnet. The magnetic field that is
produced is very similar to that of a bar magnet as shown in the picture below.
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source http://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/E2/pelect2.gif
The strength of the magnetic field produced by this current is affected by the
strength of the current, the number of loops, the size of the loops, and the material
that the loops surround.
Morning Session
Building a Simple Motor
The motor building section of this lab was adapted from the following two
webpages
http://sci-toys.com/scitoys/scitoys/electro/electro.html
http://www.msichicago.org/online-science/activities/activity-detail/activities/buildan-electric-motor/
We are going to start the lab by building for ourselves a simple motor. For our
purposes, we can consider a motor to be a device that takes electrical energy (in
this case from a battery) and converts it to mechanical energy (the spinning of a
coil). This motor will be a little too simple to actually power anything useful but the
very same principles at work here are used in all electric motors!
Here's the Materials You'll Need:
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Three ring-shaped magnets
Insulated wire
Wire cutters / strippers
One D-size battery
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Two large paper clips
Tape
Wrap the wire around the battery to make a coil. Be certain that there are
between 20 and 50 loops in your coil. Pull the wire off the battery being careful to
make sure that the coil does not lose its shape.
Use the two free ends to wrap around the loops to secure the coil. Be sure that
there is about an inch of straight wire leading off each side of the coil. See the
picture below to help guide you
Question
Notice that the wire you are using is insulated. Why do you think that we need to
use insulated wire for constructing our coils?
Hold the coil at the edge of a table, so the coil is staight up and down (not flat on
the table), and one of the free wire ends is lying flat on the table. Use sandpaper to
remove the top half of the insulation from the free wire end. Be careful to leave the
bottom half of the wire with the insulation intact. The top half of the wire will be
shiny bare copper, and the bottom half will be the color of the insulation (red).
Bend the large paper clips so that the smaller bend becomes the base and the
larger bend is made into a loop. These are the holders for the coil.
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Put the magnets on the foam and place a paper-clip holder on each side of the
magnet, with the paper-clip bases extending away from the magnet. Position the
coil above the magnets, with its arms resting in the loops of the paper-clip holders.
When the coil is turned vertically, the bottom of the coil should be about 1
centimeter above the magnet. Attach one short wire to each paper clip by putting
the end under the paper clip base.
Tape the remaining free ends of the short wires to the ends of the battery. Give
the coil a gentle spin, and watch what happens. Warning: Disconnect the electric
motor when not using, or after a few minutes of use because the circuit will get
hot. Your motor should look something like the picture below when completed.
Building an electric motor requires patience and tinkering. If your motor doesn’t
work, check this:
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Is it on a level surface?
Is the coil well balanced? It should spin without wobbling.
Try spinning the coil in both directions. It may work in one direction but not
the other.
 Make sure the wires are making good electrical contact with the battery
terminals and the paper clips.
 Flip the magnets over so that the opposite pole is facing the coil.
 Make sure the insulation is completely scraped off the arms of the coil.
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
Check the clearance between the bottom of the coil and the magnets. It
should be about 1 centimeter. (close but not touching)
 Make sure the loops in the paper-clip holders are about the same height.
What's Happening?
Remember that when a current flows through a coil of wire, the coil becomes an
electromagnet. The direction of the current determines the polarity of the
magnetic field. One side of the coil becomes the north pole, and the opposite
side becomes the south pole. As with all magnets, opposite magnetic poles attract
and like magnetic poles repel. The magnet placed under the coil attracts its
opposite pole on the coil and repels its like pole, causing the coil to spin.
Since the arms of the coil only have insulation on one half, electric current only
passes through when the uninsulated part of the wire touches the paperclips.
When the coil swings around and the insulated part of the wire touches the
paperclips, the current is interrupted, stopping its magnetic field for half a turn.
When the current flows through the coil again, the two magnetic poles either repel
or attract each other once more. After the coil starts spinning, this
spinning carries the coil through the part of its cycle when there is no current.
Motor in Reverse: A Generator
The function of an electric motor is to take electrical energy and convert it into
kinetic energy. In the motor that you built, the electrical energy in the battery is
converted into the kinetic energy of the rotating coils. If you disconnect the
battery, your motor can actually be used to produce electricity! If you spin your
coil by hand near the stack of magnets a small voltage will be created.
Unfortunately, you motor is a bit too puny to produce a measureable amount of
electricity.
Question
Give some ideas for how you might change change your motor to allow it to
produce more electricity.
This process of producing electricity is called electromagnetic induction. Any time
that there are loops of wire near a magnetic field, there is the possibility for
electromagnetic induction to occur. Electromagnetic induction is a dynamic
process. This means that it will only occur when something is changing with time.
So for electromagnetic induction to occur, one or more of the following four things
must be happening
1. Changing the size of the magnetic field. This is pretty hard with a permanent
magnet, like the ones you used in your motor. But remember from the background
that coils of wire with current flowing in them produce a magnetic field just like a
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permanet magnet. Also remember that the size of the magnetic field depends on
the amount of current flowing in the coils.
2. Changing the area of the loop(s).
3. Changing the number of loops.
4. Changing the orientation between the loops and the magnetic field
Question
When you are rotating the loops of wire in the motor that you built, which of the
above four things is occurring?
Now we will use a slightly more advanced motor to demonstrate induction. To
produce the electricity we will spin the motor by hand. To measure our efforts, we
will use a tool called a multimeter. A multimeter can be used to measure the
voltage or current produced as we spin the shaft of the motor.
Now you will get to look inside one of these slightly more advanced motors. Take
apart the motor and try to identify the parts inside this motor that have the same
function as the parts in the motor that you made.
Question
List some of the improvements that were made on this motor compared to the one
that you made. Are any of the improvements ones that you suggested in the
above question?
As a hint if things to come, we will use this idea of a motor as a generator in this
afternoon's lab. You will get to design a windmil. The spinning of your windmill
will spin the shaft of a motor and produce electricity through electromagnetic
induction.
Faraday Flashlights
The last example of electromagnetic induction we will look at today is called a
Faraday Flashlight. Inside this flashlight is a magnet which moves straight up and
down inside a coil of wire. As explained above, this will induce a voltage in the coil.
The coil is connected to a capacitor. For our purposes, it is not important to
understand how a capacitor works. The important point is the voltage causes a
current to flow that will charge the capacitor. In this way, the capacitor essentially
acts as a short term battery to power the flashlight. So you can have a flashlight
that never needs to have batteries recharged or replaced. Whenever you need
light, just shake the flashlight for a little while and the magic of electromagnetic
induction gives you the electrical energy you need to power the flashlight!
Afternoon Session
Afternoon Session
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This afternoon we are going to investigate two different ways to produce electricity.
Tying in with the sustainability theme, both these methods will be pollution
free. First off, we are going to pedal a bicycle and convert this kinetic energy into
electricity. Then we are going to divide up into teams of two and build a windmill.
The wind will turn the blades on the windmill and then this kinetic energy is going
to be converted into electricity. In both cases, as we discovered this morning,
kinetic energy is converted into electricity by reversing an electric motor to create a
generator.
Bike Machines
In this part of this afternoon's lab, we are going to use our awesome leg power to
generate electricity by cycling a bike.
Question
When you cycle a bike you create kinetic energy, where does this energy originally
come from?
When we cycle the bike, the bike wheel in turn rotate the shaft of the electric
motor, which in turn generates electricity and this is measured using the apparatus
provided. We want to measure the amount of electricity produced at different
cycling speeds (revolutions per minute or RPM). Carrying out this portion of the
lab will involve some amount of teamwork, for each measurement we will need
one person on the bike, one counting the wheel revolutions and another
monitoring the voltmeter.
After cycling the bike for a minute to get used to the setup, choose four RPM's and
practice keeping this constant. Start with the lowest one and cycle this for
30seconds. During this time another team member will have counted the total
number of wheel revolutions and another team member will be responsible for
recording the power generated. This process should be repeated at the four
different RPM's.
Once all this data is tabulated, we will graph it to compare the RPM to power
generated (actually voltage)?.
Question
What was the most efficient cycling speed?
Wind Powered Generators
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In this part of the lab you will be working with a partner to try and design the most
efficient windmill possible with the available resources. This is a competition, and
the winner will be declared based on the windmill that is able to generate the most
energy over a period of one minute. To make the comparison fair, the "wind" will
be provided by a fan set to the same speed for all of the groups.
You and your partner will be responsible for designing and constructing the blades
that will attach to the generator. The design requirements are pretty minimal
Your design must have a central cork piece for attachment to the motor/generator.
Your design must ultilize only the materials that are provided.
Here a couple of existing designs that you can use to give you a place to start.
The key will be for your group to innovate and modify them to create the most
efficient windmill. Of course, if your group has a totally new idea that is completely
different than these starting points, we encourage you to pursue those ideas as
well.
Design 1: Pinwheel
As you might guess from the name, this design resembles a pinwheel. In this
design, the pinwheel is attached to the central axis of the central cork. The basic
design is shown in the picture below:
Souce http://www.josepino.com/other_projects/index.php?howto_pinwheel.jpc
Possible Modifications
Type of material:
Paper is lighter but more flimsy. Paperboard is heavier, but more sturdy.
The size of the pinwheel:
A larger size will have a larger area, so it will collect more wind. However, the
larger size also means more weight.
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The number of blades:
The basic design has four blades in it. You could modify this to have more or less
blades by adding or subtracting the number of cuts that you make.
Design 2: Your Standard Fan
As you might guess from the name, this design resembles a fan, like a ceiling fan.
In this design the blades must be attached to the outer side of the central cork.
Possible Modifications
Type of material:
Paper is lighter but more flimsy. Paperboard is heavier, but more sturdy.
Blade attachment:
There are many possibilities for how you attach the blades to the cork.
The blades must be tilted at an angle relative to the wind direction to ensure that
the windmill spins. That amount of this tilt is another adjustable parameter.
Blades:
The number of blades you use is an adjustable part of this design.
A larger size will have a larger area, so it will collect more wind. However, the
larger size also means more weight.
The shape of the blades is also something that you can adjust.
Testing your design
To determine the power output of your windmill, we will use some of the concepts
we learned this morning. We will attach the cork piece in your windmill to a small,
unpowered motor. A fan at constant (angular) speed will provide the "wind" for
the windmill.
Question
Using your knowledge gained this morning, describe the electrical effects that will
be produced once the cork piece starts to turn the motor.
Once you have answered the above question and completed construction bring
your windmill over to the "testing facility." You will have to explain your answer to
the above question before we test the power produced by your windmill.
Big Questions
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1) Electricity is clearly very important in our lives, we use it to power many of the
devices
we now take for granted. We also know that in general when electricity is
produced we create pollution.
We saw that we can generate electricity using some apparantly pollution free
methods, a bicycle and a wind generator.
What are the benefits of having pollution free methods of electricity production?
Are the bicycle and the wind generator really pollution free?
2) Some car companies now manufacture cars which use electric motors. Unlike
normal
cars we see on the road these cars don't belch smoke out of their tailpipes. Do
these really
pollute less than conventional gasoline driven cars?
3.
We have compiled a list of several items in our technological society that use a
motor or electromagnetic induction to function. Choose the one that you think has
the largest impact on life in our society. Feel free to think of a
different technological item not on the list that you think is the most important in
everyday life. Ask one of the teaching assistants and we will tell you if it uses
induction or a motor or not.
Once you have chosen your item, write about the following:
(a) Explain why you think that your choice is the most influential in our daily lives.
(b) Use your imagine to describe how you think life would be different without this
particular item.
Examples:
Computer hard drive, back-up electrical system in an airplane, several
components in any car, electric guitar, a hybrid car, airport metal detectors, ATM
and credit card readers, electrical transformers (used in electricity generation for
your home, businesses, etc.), battery chargers, cell phones, radios, television, and
many many more.
4.
(a) Write about what you think would be some of the pros and cons of using wind
power.
(b) Hydroelectric power uses the same technology as windmills to create
electricity. This difference is that water falling from a waterfall spins the turbines
instead of wind. Do you think Chicago would be a good place for implementing
wind power, hydoelectric power, or neither? Be sure to explain your answer.
Hints for part (a) in case they are having some trouble:
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Pros: Essentially zero emissions, renewable, free "fuel", less infrastructure
necessary, no dependence on foreign fuel sources, minimal impact on natural
habitat, phased growth, price stability
Cons: High costs of initial investment, some people think windmills are not visually
pleasing,
5.
The sun is the ultimate source for nearly all of the energy on our planet.
(a) Describe each of the energy conversion steps that ultimately lead to the light
bulb attached to the bicycle lighting up. You should begin with the nuclear
reactions in the sun and end with the bulb lighting up. Make sure that you include
the two types of energy involved in each of the conversions.
(b) Choose the conversion step that you think is most inefficient and explain why
you think this is the most inefficient step.
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