Electricity and Magnetism, Part 4 Rationale: According to the California State Science Content Standards, electricity and magnetism are important concepts for 4th grade students. Disclaimer: Some of the procedures for the activities contained in the lessons have been adapted from various resources listed throughout the module. Part 4: Electricity, Magnetism, and Work applications of electricity and magnetism • • • • • Activity Summary: Observe current induction by moving magnetic field Investigate parameters for changing induced current Complimentary behavior – speaker experiment Build motor Generate electricity • • • • File Summary: E&M_4_doc E&M_4_teachers E&M_4_wksht E&M_4_wksht_key Page 1 Part 4 Worksheet Item 1 Part 4 Worksheet Item 2 Part 4 Worksheet Item 3 Part 4 Worksheet Item 4 Electricity and Magnetism, Part 4 Part 4: Magnetism, Electricity, and Work Objectives: After participating in the program Electricity and Magnetism, Part 4, students will be able to: • explain that a magnetic field changing with time produces a current in a wire • describe how the current produced in a wire by a moving magnetic field changes direction as the motion changes direction • report that the current produced in a wire by a moving magnetic field will vary in magnitude as the number of coils is varied and if a magnetic core is used • recognize that movement (of a diaphragm of a speaker or the rotor of a motor) can be produced by forcing a current through a coil near a stationary permanent magnet • describe how electric power may be generated by causing a magnet to move near a coil of wire Lesson Plan: Materials: For each group: • coil of wire with number of turns labeled on it • 2 permanent magnets • magnet wire (24 gauge, about 1 m long) • sandpaper • ammeter (-250 µA to + 250 µA is ideal) • straw • large iron-containing nail • small speaker • 2 electrical leads with alligator clips • 1 D-cell battery and battery holder • empty 35 mm film canister (or D-cell battery) • wooden support (for motor, 8” x 8” x ½” pieces of plywood) • 2 large paper clips • needle nose pliers • tape For each student: • worksheet For the teacher: • one small speaker taken apart to show parts For the class: • hand-cranked generator with LED (Carolina Biological Supply) Time: activity 1: activity 2: activity 3: activity 4: activity 5: 15 minutes 10 minutes 10 minutes 40 minutes 15 minutes Page 2 Electricity and Magnetism, Part 4 Volunteer/Teacher Preparation: 1. Wind the coils: Use large spools such as those used for gift wrap ribbon. This will make it easier to wind the wire as well as to move the magnets inside the spool. Use magnet wire which has an enamel insulation on it. Leave about 4” at both ends of the wire free so that you can access them after the coil is finished. Wind the wire tightly and neatly around the spool. Try not to let the adjacent coils overlap each other. As you finish one layer, put a paper layer on top and secure with tape. Continue wrapping the next layer of coils on top of the paper. When you have the desired number of turns, complete the spool with another layer of paper. Cover the final paper layer with tape so that the coils may be handled easily. Sand off about 1” of insulation at both ends of the wire in order to make electrical contact. Label the spool with the number of turns it contains. With 160 turns of 24 gauge wire wound around a spool with an inside diameter of 2 ¾”, you can produce a good deflection on the ammeters specified above. The stronger the magnets you use, the more deflection you will see. A cow magnet will yield very large deflections on your ammeter. If the magnets are the typical disk shaped magnets commonly available in large quantities, you may want to ask the students to use 2 or 3 magnets at the same time to do this experiment. For making coils with different numbers of turns, use a factor of 2 or 3 times the lowest number of turns you will be using in order to see a difference in experimental results. For example, you could use spools with 160 and 320 (and 480) turns. Make sure all spools are the same size and are wrapped with the same gauge wire. 2. Take a small speaker apart. Gently remove the black paper that forms the diaphragm. This will reveal the coil which can move in and out of a slot around a cylindrical permanent magnet. Students will energize their speakers in order to feel and see the movement of the coil in and out of the slot around the magnet. Activities: 1. (15 minutes) • Have students choose a spool with wire coiled around it. • Check the wire ends to make sure they have been sanded clean. • Next, have the students build a circuit with the coil and an ammeter in series. • Move the magnets near the coil (move it inside the spool if possible) while watching the ammeter. • Students should record their observations in the worksheet. • What determines the magnitude and direction of the current flow? 2. (10 minutes) • Have the students exchange spools with another group (to try a different number of turns), change the speed of the magnet, and introduce the large nail inside the coil. • How does the current change when you change how fast you move the magnet? • What happens when you repeat the exercise with the large nail inside the coil? • What is the effect of using a coil with a different number of turns? Page 3 Electricity and Magnetism, Part 4 3. (10 minutes) • Do we see complementary behavior if the magnet is held stationary and a current is made to flow through the coil? Ask the students to try holding the magnet still and moving the coil. (This is the how a speaker works.) • Have the students make a new circuit with two leads, a speaker, and a battery. Keep one lead disconnected so that it can be connected momentarily by touching the alligator clip to the appropriate contact. • Notice the movement of the speaker when the connection is made. (Students can both see and feel this movement. The movement is reversed when the connection is broken. The sound is heard only once, when the connection is made.) • Students should record their findings on the worksheets. 4. (40 minutes) • Can we use the motion produced by running a current through a coil near a permanent magnet to do work? (Yes, this is the principle of a motor.) • Have students build the motor2,8. (When operating the motors, take care that the batteries are not connected too long (overheated wires and battery life). The students will be guided through this process, step by step.) • As they go, students should record on their worksheets what was done in some way (such as a schematic with a few notes, etc.). To make the motor2,8: • Refer to figure E&M_4_1 during construction of the motor. • Sand off about 1” of insulation at one end of the magnet wire. • Sand off about 1” of the insulation at the other end of the magnet wire on only half of the wire – make sure that half of the wire still has insulation on it. • Wrap the wire around the film canister or D-cell battery leaving about 3” on either end of the coil. • On each side, wrap the remaining wire around the coil to hold it together. Make sure these wraps are 180° apart so that the coil is balanced. There should now be about 1” of wire sticking straight out on either side of this coil. • Bend out the inner small loop of a large paper clip. This smaller loop should be at 90° to the larger loop. • With needle nose pliers, bend half of the smaller loop parallel with the other half to form a hook for the wires to rest on. • Repeat this with another paper clip. • Tape the larger loops of the paper clip to the wooden support board. The placement should be far enough apart so that the extended wires of the coil rests on these two supports and can rotate freely. • Make sure that the sanded portions of the wire ends are in contact with the paper clips. • Place a magnet (or use two magnets) directly underneath the coil (with tape if desired). • Check to see that the coil can still rotate freely. • Connect the battery terminals to the paper clips with alligator clip leads. • You will probably have to nudge the coil to get it started. If balanced properly, the motor will rotate until the circuit is opened. Make sure to run the motor for only about 10 seconds to avoid overheating and running the battery down. Page 4 Electricity and Magnetism, Part 4 E&M_4_1. Illustration of motor construction. a) sand insulation off one end of magnet wire and off half of the other end: b) wrap wire around film canister to form coil: c) remove coil from canister and wrap ends around coil to secure: d) bend paper clips: e) assemble motor: + Page 5 Electricity and Magnetism, Part 4 5. (15 minutes) • The motor uses the magnet and an electrical energy source to produce motion (and do work). What would we have to do to generate electricity? (The obvious solution based on today’s lesson plan would be to cause a magnet to move near a coil of wire, thereby producing current in that wire (mechanical work is converted to electrical energy). This is exactly how PGE generates electricity.) • Ask the students for ideas for how the magnet could be moved. (wind, steam, water turbines) • Let them take turns turning the crank of the generator to light up the LED. References and Extension Ideas: The following resources were used in developing this lesson plan. Some of the activities were adapted from these sources. Many ideas for extension activities can be found in them as well. 1. The Thomas Edison Book of Easy and Incredible Experiments, Thomas Alva Edison Foundation, John Wiley & Sons, Inc., New York, 1988. 2. www.beakman.com 3. Foss Magnetism and Electricity Module 4. www.freeweb.pdq.net/headstrong/mag.htm 5. www.freeweb.pdq.net/headstrong/mag2.htm 6. www.pausd.palo-alto.ca.us/k6science/electric/e_tips.html 7. www.edtech.kennesaw.edu/web/electric.html 8. Exploratorium Science Snackbook or www.exploratorium.edu/snacks/ 9. www.pbs.org/ktca/newtons/12/electric.html 10. www.pbs.org/wgbh/nova/teachersguide/lightning/lightning_sp1.html 11. www.pbs.org/wgbh/nova/specialfx/fxguide/fxmshtr2.html 12. www.pbs.org/saf/4_class/45_pguides/pguide_605/4565_image.html 13. www.pgs.org/saf/4_class/45_pguides/pguide_604/4564_shark.html 14. www.pgs.org/saf/4_class/45_pguides/pguide_602/4542_storm.html 15. www.chss.montclair.edu/~pererat/pertel.html 16. www.chss.montclair.edu/~peretat/perbuild.html 17. www.chss.montclair.edu/~pererat/perwirls.html 18. The Science Teacher, October 1999, “Electromagnetic/Mechanical Resonator”, pp. 56-58. Page 6