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    Using "Student Power" to Generate Electricity to Run a Portable Compact Disc Player
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    "Student Power" Experiment

    This experiment is courtesy of 

    Using "Student Power" to Generate Electricity to Run a Portable Compact Disc Player


    Jennifer Brittain
    P.A. Guth Elementary School, Perkasie, PA

    Mario Mirabelli
    Senior Research Chemist, Rohm and Haas Company

    Mark Silvano
    Junior Research Chemist, Rohm and Haas Company

    Frank Letterio
    Laboratory Technician, Rohm and Haas Company


    Grade Level:

    3 through 6



    Physical Science - Magnetism and Energy



    Upon completion of this unit, the student will:

    1. Conclude that magnets and magnetic fields can produce electricity.
    2. Understand how a small motor works.
    3. Understand how gears work.
    4. Describe how energy can transform along a pathway.



    Pedal Powering the Compact Disk Player


    Upon completion of this activity, the students will:

    1. Identify potential sources of energy.
    2. Describe the transformation of the energy of this system and ones similar.

    Apparatus Description/Background:

    The apparatus pictured in Figure 1 is the one developed at the Rohm and Haas Laboratory. For a technical explanation of this device and its components, please see Appendix A. A simpler set up can also be created to achieve similar results. You will need a small motor and a gear box (see Appendix C) mounted to something, like a piece of wood, which can be held or C-clamped onto a table for stability. We assume that it may also be possible to use a regular, geared bicycle. We used an adapted version because the smaller set up seemed to make a lot of noise, therefore making the CD less audible. The electric generator displayed in Figure 1 can produce a potential of approximately 3 volts or more when the pedal is rotated at 40 revolutions/minute. This is the equivalent of two dry cell alkaline batteries when placed in a series configuration (nominal voltage of 1.5 volts/cell). Therefore, this generator is limited to powering small direct current devices, which require a maximum of two batteries. One device, which fits this requirement, is a portable CD player. However, any device requiring one or two alkaline batteries will suffice, especially if you are unable to overcome the noise the device itself makes.


    There are many different forms of energy. These forms can be divided into six main groups. These groups are mechanical energy, heat energy, electrical energy, chemical energy, nuclear energy, and wave energy (like sound energy and radiant energy). A simple example of how energy transforms could start with the sun. The sun gives energy to the plants so they can make their own food. When people or animals eat the plants they receive the stored energy. People then use the energy they get from plants to move things, like a crank. Here they are changing chemical energy to mechanical energy. The crank is attached to the gears and a generator, which changes the mechanical energy to electrical energy. The electrical energy spins the CD player changing electrical energy back into mechanical energy and radiant energy. Then they change into wave energy (sound waves), and we are able to hear the music.

    The generation and transmission of energy from power plant to user involves many transformations of energy. To produce electricity most power plants burn fossil fuels like oil, natural gas, or coal. When these fuels are burned the heat they produce is used to boil water. The boiling water produces steam. This steam is then used to turn a turbine. These turbines turn the coils, or magnets, of a generator to produce electric current. (Any time a conducting material moves through a magnetic field an electric field is generated in the conductor. If the conductor forms part of a closed circuit, current will flow.) Transformers are then used to increase or decrease the voltage of the current that travels through the wires so it can travel long distances, and safely be used in the home (the transformer step has been left out of the activity that follows). Turbines could also be turned by wind, or falling water.



    Investigation One - Transformation and Pathways of Energy

    Activity One - Forms of Energy


    "bicycle generator", drawing paper, colored pencils or crayons


    Involve the students in the operation of the "bicycle generator". Hold a discussion about the different forms of energy and where they could be applied to the apparatus. Discuss the transformation through that pathway, then have the student suggest similar examples. Have the students draw their own example of a pathway. Be sure to have them also write about the transformations that are taking place.

    Have the students brainstorm ideas about how else the "bicycle generator" could be powered.

    Activity Two- Pathway Game


    Pathway cards, Student Worksheet

    Teacher Preparation:

    When using groups of four to six students, copy only one of the energy source pages per group and 6 to 8 copies of the path cards. Cut the copied sheets into uniform pieces. Each group will need a set of cards.


    Discuss with students the path that must be traveled in order to provide electricity to their home. Place the students into groups of four, five, or six. The number of students in the group will affect the cards that are needed. The game is played like "Go Fish". There are four different energy resources, and to start a pathway the student only needs one of the four sources. To complete a pathway the student needs one each of the rest of the cards. When a student collects all the cards of the pathway in their hand. They may lay them down to win the game. However, if they are unable to describe the transformations that are taking place, they should not be declared a winner. Play should start over.


    Students should complete worksheet when game play is concluded.


    Worksheets for Investigation 1 are available for download in PDF format:

      student_power1.pdf  (161K)  Get Acrobat Reader



    Magnets and Electromagnets


    Upon completion of this activity, the students will be able to:

    1. Identify magnetic materials.
    2. Explain that similar poles of a magnet repel and opposite poles attract each other.
    3. Describe how magnetism can be created in an electromagnet.
    4. Identify variables that effect the magnetism of an electromagnet.
    5. Identify devices that incorporate electromagnets.


    Magnets that exist in nature are called lodestones. Man-made magnets can be created with materials that contain iron, steel, cobalt, and nickel. Scientists believe that magnetism is due to the movement and alignment of the electrons around the nucleus of an atom.

    Temporary magnets can be created from materials like soft iron by induction (by bringing the material into proximity of a magnet, or having it touch a magnet), by stroking it with a magnet in one direction to help align the molecules, or by wrapping it with wire and attaching it to a dry cell. The last example of a temporary magnet is called an electromagnet. Electromagnets have a north-seeking and a south-seeking pole just like other magnets, but these poles can be reversed if the electric current is reversed. Electromagnets can also be strengthened by increasing the amount of electrical current flowing through the wire, by increasing the amount of turns of wire that are around the core, and by using a U-shaped core. Electromagnets are used in many household devices like a phone, many electrical appliances, and most electrical toys.



    Investigation Two - Magnetic Forces

    Set up several experimental stations where the students can experiment with magnets or do as a teacher demonstration. Below are some suggested activities.

    Activity One - Determining Materials that are attracted to Magnets


    Magnets of different shapes, sizes, and strengths; Materials to be tested - tacks, brads, staples, rubber bands, aluminum foil, different coins (especially old Canadian nickels, which have more nickel in them), glass, chalk, etc., Student Worksheet.


    Have the students try to pick up a variety of materials with magnets.


    Have them record their findings on the worksheet (What's Attractive) and make a conclusion about them to be discussed with others.


    Have the students test their predictions about other materials from the conclusions on their worksheet.

    Activity Two - Magnet Poles


    Magnets of different shapes, sizes, and strengths, Iron filings (tacks or paper clips may also be used and are not as messy), Student Worksheet.


    Using the different shaped magnets, have the students record where on the magnets iron filing will stick to each by drawing a picture. Have them also experiment to see where and how the magnets stick to each other.


    Have the students write down a conclusion (Stick To It Worksheet) about their findings to be discussed with others.

    Activity Three - How Magnet Poles Interact


    Ruler; String; Copper wire; Two magnets (per group) with color-coded or labeled (N or S) ends.


    Attach the copper wire to the magnet to form a balanced support where you can connect the string so that the magnet may swing freely. Suspend that magnet away from any metal objects by attaching the string to a ruler that can be inserted into a stack of books. Label the poles by using different colors and/or the letters N and S. Take another magnet (match the colors/labels to the N and S poles of the suspended magnet) and have the students try to spin the suspended magnet with out getting them stuck together.


    Have the students write down a conclusion about how the ends of the magnets affect each other to be discussed by the class. Students could use the color terms at first, then replace them with the terms north-seeking and south-seeking poles after further discussion.

    See Appendix B for some great internet sites that have other magnet experiments and some additional background information.


    Worksheets for Investigation 2 are available for download in PDF format:

      student_power2.pdf  (6K)  Get Acrobat Reader



    Investigation Three - Creating an Electromagnet


    Lantern battery ("D" size will work, but is harder to make safe connections); Paper clips or tacks; 2 -3 feet of insulated copper wire; Soft iron nail


    Expose the ends of the copper wire. These ends should then be connected to some wire clips and covered with electrical tape (the exposed wire heats up quickly if left attached to the battery - this will also drain the battery quickly if the connections are left attached). Wrap the wire around the nail 5 times. Have the students attempt to attach the clips or tacks and record their findings. Then wrap the nail with 10 coils of wire and repeat. Continue this process, increasing the amount of coils each time by 5 until you get to somewhere around 25 or 30.


    Have the students draw a conclusion about how the number of coils affect the strength of the electromagnet. (Creating an Electromagnet Worksheet). Discuss the variables which may affect each groups results (like battery strength, quality of the coil, differences in weight of clips or tacks, placement of those objects on the nail, etc...). Discuss ways to make an electromagnet stronger (more batteries, more coils).

    For similar experiments see Appendix B.


    Examine how a nail may become magnetized without the current flow. Discuss ways to create and destroy magnetism in something.


    Worksheets for Investigation 3 are available for download in PDF format:

      student_power3.pdf  (5K)  Get Acrobat Reader



    Simple Motor


    Upon completion of this activity, the student will be able to:

    1. Identify the parts of a simple motor.
    2. Describe how electric energy is transformed to mechanical energy.


    A motor is the opposite of a generator since it turns electrical energy into mechanical energy (see background from the section about transformation and pathways), and uses electricity to produce magnetism. Electromagnets are used in motors. Most motors have an armature, commutator, permanent magnet, brushes and a power source. The motor works in the following way. Current travels from the brushes to the commutator, into the armature. The armature contains the coiled wire and becomes the electromagnet. The north-seeking pole of the electromagnet will be attracted to the south-seeking pole of the permanent magnet causing the armature to move. When the armature rotates it will eventually reach a position where the brushes lose, then reestablish, contact with the commutator. This will then cause a reverse in the current through the armature, and a reverse of its poles. This reversing of current and changing of poles causes the motor to continue to spin until the electrical current is removed.


    See Appendix B for some extensive background information about how motors work, and the steps to creating this small motor.


    See Appendix B for information on the construction of the motor. When creating the motor here are some things we found that improved the motor:
    Use a small gauge wire (20 -24 gauge).
    Be sure that the coil is small and balanced.
    Use a very strong magnet.
    Use electrical tape instead of rubber bands.
    Have patience!

    Good luck! There are also many similar models for this motor, and even some commercially made kits.


    Discuss with the students what work this motor could do.





    Upon completion of this activity, the student will be able to:

    1. Identify how to calculate gear ratios.
    2. Explain the rationale for using gears.


    The purpose of using gears is to change the distance a bike, for example, moves forward with each pedal stroke. The gear ratio of the "bicycle generator" was calculated to be approximately 240 : 1. This means that for every revolution of the generator pedal, the shaft will rotate 240 times. A normal bicycle tire is about 26 inches in diameter. By taking the diameter of the wheel times _ you would be able to calculate the circumference of the wheel which translates into the distance the bike will travel. This activity will help the students get a feel for how gears change the revolutions needed per minute to generate enough power to run the CD player.

    Investigation Four - Gear Ratio


    Five to seven geared bicycles (or may use one and do as a demonstration), Student Worksheet.


    Have each bicycle set to a different gear. Invert the bicycles. (The next step may be skipped depending on the level of competency you feel your students would have at remembering the starting and stopping point of the pedal and the wheel at each station.) On the side of the back wheel of a geared bicycle place a line, or bright colored tape, to establish a starting point. Place a piece of tape on the floor under the wheel to be lined up for the purpose of counting the revolutions. Place a similar line on the floor straight under the pedal when the pedal is in the down position.


    Have the students record the number of wheel turns associated with each pedal turn on the worksheet. This sheet may need to be adapted to the level of the students.


    Find the circumference of each tire and calculate the distance the bicycle would travel.


    Worksheets for Investigation 4 are available for download in PDF format:

      student_power4.pdf  (6K)  Get Acrobat Reader



    Appendix A

    Figure 2

    Technical Explanation of the Construction of the Electric Generator

    The electric generator utilized in this experiment was constructed from a modified stationary exercise bicycle coupled to a simple DC electric motor (Figure 1). By rotating the shaft of the electric motor, a potential difference (voltage) is created at the positive and negative leads, which can be used to power a portable DC device. In order to achieve the necessary rotation of the motor shaft (for the motors that we tested, a shaft rotation speed of 5000-10,000 rpm was necessary in order to achieve a voltage of 3 volts), the motor is attached to a gearbox and coupled to the flywheel of the stationary bicycle (Figure 1). Attaching the motor in this manner allows for a higher gear ratio, thus reducing the necessary rotation speed of the bicycle pedal to a more manageable level.

    For the device in Figure 2, the motor is directly coupled to a 2.5:1 gearbox, which is in contact with an 8.25-inch flywheel. The gearbox shaft contacts the bicycle flywheel via a battery terminal nut, which was bored out to fit over the gearbox shaft. The knurled section of the battery terminal nut was grooved to facilitate an O-ring ("tire") while the entire device is held onto the shaft with a setscrew. The flywheel is attached to the bike pedal via a separate gearbox (~6:1 gear ratio) which results in an overall gear ratio of approximately 240:1.

    For the device in Figure 2, the motor is directly coupled to a 2.5:1 gearbox, which is in contact with an 8.25-inch flywheel. The gearbox shaft contacts the bicycle flywheel via a battery terminal nut, which was bored out to fit over the gearbox shaft. The knurled section of the battery terminal nut was grooved to facilitate an O-ring ("tire") while the entire device is held onto the shaft with a setscrew. The flywheel is attached to the bike pedal via a separate gearbox (~6:1 gear ratio) which results in an overall gear ratio of approximately 240:1.

    There are many possible variations to the apparatus described above. One can envision utilizing a geared bicycle in an inverted position and contacting the bicycle wheel with the output shaft of the motor gearbox (as described above). The gear ratio can be conveniently changed using the bicycle derailleur and the bicycle could be hand cranked to provide the power.

    Operation of a Portable CD Player.

    The CD player was modified to accept alligator clip connectors so that easy connections could be made to the motor. The positive and negative terminals of the motor were connected to the positive and negative terminals of the CD player (found in the battery compartment). It is important to ensure that the polarity of the circuit is correct; some devices can be damaged if set up in the reverse direction. In addition, it is important to determine the proper rotation direction on the pedal. Only rotation in one direction (clockwise or counter clockwise) will produce a positive voltage. Rotation in the other direction will produce a negative voltage and some control procedure should be put in place to prevent exposure of the electronic device to a negative voltage. Once these connections are secured, a second set of alligator clips is fastened to the motor terminals in order to attach a digital voltmeter. This voltmeter is a necessary component of this system. The digital voltmeter allows the operator of the system a visual display of the applied voltage, thus aiding in determining and maintaining the proper rotation rate. The CD player will only operate when the external voltage is within a range of 2.2-3.2 volts. A voltage of less than 2.2 volts or greater than 3.2 volts results in disruption of sound, requiring a complete restart of the system.

    Once the electrical connections have been made and the proper direction of rotation has been determined, the unit is ready for operation. While headphones can be used to listen to the music, a small set of amplified computer speakers would be more appropriate for a classroom demonstration. Place a CD into the unit and begin rotating the pedal until a voltage of approximately 2.5-3.0 volts is achieved and maintained (Note: Some portable CD players are equipped with a separate on-off power switch. If this is the case, the voltage must be applied to the unit prior to turning it on.) Once the external voltage is maintained in the desired range, hit the "Play" button and enjoy your favorite music. As long as the pedal is turning, the music will play.



    Appendix B

    Internet Resources:

    Magnet Experiments




    How a Motor Works


    Building a Simple Motor




    Victor, Edward. Science for the Elementary School. New York: Macmillan Publishing Company, 1985. 768 pp.
    Addison-Wesley Science, Sixth Grade Edition, 1989.

    Commercial Kits

    Adventures in Science - Magnetism from Educational Insights
    Electro-Magnetix from Educational Design, Inc.



    Appendix C


    Radio Shack and Hobby Shops
    Delta Education - http://www.delta-education.com / 1-800-801-7083
    Fisher Scientific Company - http://www.fishersci.com / Fax: 412-490-8304
    Science Stuff - http://www.sciencestuff.com / 1-800-795-7315

    This experiment is courtesy of 

    My Dog Kelly

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    Last updated: January 2011
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