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Transcript
Electricity and Magnetism Electromagnets Purpose To construct an electromagnet and change its strength by manipulating different variables. Process Skills Observe, measure, form a hypothesis, collect data, interpret data, identify and control variables, communicate, draw conclusions Background Magnetism is an invisible force caused by moving electrons. Magnets form when those electrons line up, creating magnetic force at opposite (north and south) poles. An object that has been magnetized will attract ferrous metals (such as iron, cobalt, and nickel). Materials q data sheet q 2 non-galvanized steel nails, 10 cm (4 in.) q 2 non-galvanized steel nails, 5 cm (2 in.) q 2 lengths of thinly insulated, 20-gauge wire, 30 cm (1 ft.) q 2 lengths of thinly insulated, 20-gauge wire, 60 cm (2 ft.) q wire strippers or scissors q 2 new D-cell batteries q 30 folded staples q electrical tape Permanent magnets, such as the ones on your refrigerator, keep their magnetism for a long time. Temporary magnets do not keep their magnetic properties over an extended period of time. One type of temporary magnet is an electromagnet. When it is properly connected to an electric current, the electrons within the electromagnet line up, creating a magnetic field. The magnetic field of an electromagnet can be turned on and off, depending on whether or not it is connected to an electric current. In this exploration, you + will make an electromagnet and determine how different variables can affect its strength. Safety: Electromagnets can become hot very quickly. Use caution when touching your electromagnet! Use cloth gloves if available. Disconnect wires from batteries at all times when they are not in use. Time – About 1 hour Grouping – Small groups and individuals © Learning A–Z All rights reserved. 1 www.sciencea-z.com experiment Electricity and Magnetism—Electromagnets Procedure Making Electromagnets 1.Your teacher may choose to remove the insulation from the wire ends ahead of time. If not, do so very carefully. Use the wire strippers or scissors to carefully remove about 2 cm (1 in.) of insulation from each end of all four wires. The exposed ends of each wire will later be connected to the batteries. 2.Wrap one of the 30 cm pieces of wire around a 5 cm nail 10 times. Wrap the wire tightly and neatly (see Figure A), and make sure that it is coiled in a single direction. Be sure the coils do not overlap. Leave some loose wire at each end of the nail. 5 cm nail with 10 wire coils 10 cm nail with 10 wire coils 5 cm nail with 20 wire coils 10 cm nail with 20 wire coils Hypothesis: In this activity, you will conduct tests to find out how many staples different electromagnets can pick up. You will use three variables to make electromagnets: length of nail (5 cm or 10 cm), number of wire coils around the nail (10 or 20), and number of D-cell batteries (1 or 2). With your group, discuss which of the eight possible combinations of variables you predict will pick up the most and the fewest staples, and why. Then complete the hypotheses on your own data sheet. Test 1: Electromagnets with One Battery steel nail exposed wire insulated wire 1.Pile 30 folded staples in your work area. 2.Pick up the 5 cm nail that has 10 wire coils. Tape one end of the exposed wire to each end of one D-cell battery (see Figure B). The tape must be strong enough to hold onto the nail in midair. Your nail is now an electromagnet! Figure A 3.Repeat Step 2, using your other 30 cm piece of wire, but using a 10 cm nail instead. Wrap the wire in 10 coils. D-cell battery 4.Now repeat Step 2, but wrap a 60 cm piece of wire around each of the remaining 5 cm and 10 cm nails. This time, wrap the wire in 20 coils. Once again, leave some loose wire at each end of the nail. You should now have the following nail-wire combinations: tape + steel nail insulated wire © Learning A–Z All rights reserved. 2 - exposed wire Figure B www.sciencea-z.com experiment Electricity and Magnetism—Electromagnets Test 2: Electromagnets with Two Batteries 3.Hold onto the battery, letting the coiled nail hang below it. Slowly move the nail around in the pile of staples for 5 seconds and then raise it above the pile. In a nearby area, remove the staples from your electromagnet. [Note: Immediately after removing the staples, disconnect one end of the wire from the battery. The longer you leave it connected, the hotter the wire will become!] Count the number of staples your electromagnet picked up. Record this number in the first table on your data sheet, on the appropriate row, under Trial 1. 1.Now you will repeat the entire exploration, but use two D-cell batteries instead of one. Pick up the 5 cm nail that has 10 wire coils. Tape one end of the exposed wire to one of the battery’s positive ends (the end with the + sign). Tape the other end of the exposed wire to the second battery’s negative end (the end with the – sign). Hold onto both batteries so that the first battery’s negative end touches the second battery’s positive end (see Figure C). You now have a new type of electromagnet. 4.Repeat this test two more times with the same electromagnet. [Note: Remember to disconnect one end of the wire from the battery as soon as you have removed the staples each time!] Record the results under Trial 2 and Trial 3 for this type of electromagnet. + - + - exposed wire 5.Add together the number of staples the electromagnet picked up in Trials 1, 2, and 3. Divide the total by 3. Record this number as the Average on the correct row of the data table. steel nail 6.Repeat Steps 1–5 using the 10 cm nail with 10 coils, then the 5 cm nail with 20 coils, and finally the 10 cm nail with 20 coils. [Note: Remember to disconnect one end of the wire from the battery as soon as you have removed the staples each time!] © Learning A–Z All rights reserved. tape D-cell battery 3 Figure C insulated wire 2.Repeat Test 1, but this time use the two connected batteries as you test each of your four coiled nails. Complete three trials with each electromagnet, and record all data in the second table on your data sheet. www.sciencea-z.com experiment Electricity and Magnetism—Electromagnets Data Sheet Name________________________________________ Date_____________ Hypotheses: Consider all the variable combinations in this activity (5 cm or 10 cm nail length, 10 or 20 wire coils, 1 or 2 batteries) and then complete each hypothesis. 1. Which combination of variables will pick up the most staples? Why do you think this will be so? 2. W hich combination of variables will pick up the fewest staples? Why do you think this will be so? Collect Data Test 1: Number of staples picked up when connected to one battery Electromagnet description Trial 1 Trial 2 Trial 3 Average 5 cm nail with 10 coils 10 cm nail with 10 coils 5 cm nail with 20 coils 10 cm nail with 20 coils Test 2: Number of staples picked up when connected to two batteries Electromagnet description Trial 1 Trial 2 Trial 3 Average 5 cm nail with 10 coils 10 cm nail with 10 coils 5 cm nail with 20 coils 10 cm nail with 20 coils © Learning A–Z All rights reserved. 4 www.sciencea-z.com experiment Electricity and Magnetism—Electromagnets Questions Name________________________________________ Date_____________ Analyze Data 1. When your results were averaged, which combination of three variables made your electromagnet pick up the most staples? 2. When your results were averaged, which combination of three variables made your electromagnet pick up the fewest staples? 3. Which variable affected the results most—nail length, number of coils, or number of batteries? Why do you think this variable was so important? 4. Which variable affected the results least—nail length, number of coils, or number of batteries? Why do you think this variable was not as important as the others? 5. Why was it important to conduct three trials with each electromagnet and find the average results? © Learning A–Z All rights reserved. 5 www.sciencea-z.com experiment Electricity and Magnetism—Electromagnets Questions Name________________________________________ Date_____________ Draw Conclusions 1. Would the electromagnets have worked if you had used a piece of wood or plastic instead of a nail? Why or why not? 2. Why did the safety tips suggest disconnecting just one wire from the battery instead of both wires? 3. How would you build an electromagnet that was stronger than any of the ones you used in this activity? © Learning A–Z All rights reserved. 6 www.sciencea-z.com Electricity and Magnetism Electromagnets Teaching Tips These process activities will help students understand the properties of electricity and magnetism, and the relationship between these two forces. Electricity can be observed in action both as static electricity and as an electric current. Magnetism can be applied to many familiar objects, but many other objects are not magnetic. Exploring and experimenting with variables will allow students to understand that electricity and magnetism can each be used at differing strengths and in different applications. When using electromagnetism, safety is extremely important. Set-up and procedures efore students test the electromagnets, you may want to conduct your B own investigation so you will be able to judge whether students’ results are accurate, given the available materials. ¢ Discuss the importance of wrapping the wire around the nails neatly and in the same direction. If students change the direction of their wrapping partway through, the electrons will not all align in the same direction. This will decrease the strength of the electromagnet. ¢ For increased safety during the experiment, you may wish to strip the insulation off the ends of the wires beforehand. Use wire cutters to carefully pull about 2 cm (1 in.) of insulation from each end, creating leads of exposed wire. ¢ It doesn’t matter which end of the wire is connected to the battery in terms of magnetic strength. View the wire as neutral. What will vary is the polarity (north versus south pole) of the electromagnet and the flow of electric current. ¢ To avoid distraction and maximize lab safety, pass out materials only after students have finished reading through their instructions and making their hypotheses. ¢ I f using cooperative groups, assign jobs for each student within each group. Examples include getter, recorder, wire wrapper, staple counter, materials manager, and reporter. ¢ Reinforce relevant vocabulary terms (e.g., electromagnet, magnetic field, electric current) throughout the experiment. safety ¢ ¢ © Learning A–Z All rights reserved. iscuss all safety rules prior to allowing students to begin the experiment. D Emphasize the importance of disconnecting the wires from the batteries immediately after collection of data. 1 www.sciencea-z.com experiment materials extensions and variations Electricity and Magnetism—Electromagnets ¢ The best wire to use for this experiment is magnet wire, available in electronics and hardware shops. Other types of wire, including standard electrical wire and telephone wire, will also work. ¢ Do not use galvanized nails. ¢ Have extra materials available in case of dead/weak batteries, overly stripped wire, or other material faults. ¢ Different sizes of batteries, different lengths of wire, and different sizes of nails can all be substituted in this experiment. Results will vary, and student data sheets will need to be adjusted accordingly. Remember that if stronger batteries are used, the wires will heat up faster. ¢ Variation/Inquiry ¢ Research/Technology: ¢ ¢ ¢ ¢ ¢ © Learning A–Z All rights reserved. Science: Repeat the experiment, but this time provide each group with different sizes of batteries, such as AAA, AA, C, and 9-volt. How do different sizes of batteries affect the results? Have students research how magnets work and the many uses of magnets, including electromagnets. Ask them to compile and present their research in a digital slideshow to share with other classes. ESL/ELL: Have students create a dictionary or word wall in which key vocabulary words are alphabetized, defined, and illustrated, such as: magnetism, force, electrons, north pole, south pole, metal, iron, permanent, temporary, electromagnet, electric current, and magnetic field. Home Connection/Technology: Have students search and list everything in their house that uses magnets. Compile all students’ lists into a class list. Then students can find or create images of each magnetic item to contribute to a class bulletin board or mural about magnets. Guest: Invite a radiologist to visit the class to discuss how magnets are used in medicine. Field Trip: Visit a power plant or recycling center. Ask a technician to explain the roles that magnets play. Research: See Using the Internet in the Unit Guide for suggested websites to extend the learning. 2 www.sciencea-z.com experiment Electricity and Magnetism—Electromagnets Data Sheet Answer key experiment Electricity and Magnetism—Electromagnets Data Sheet Name________________________________________ Date_____________ Hypotheses: Consider all the variable combinations in this activity (5 cm or 10 cm nail length, 10 or 20 wire coils, 1 or 2 batteries) and then complete each hypothesis. 1. Which combination of variables will pick up the most staples? Why do you think this will be so? Hypotheses will vary and should be supported by logical reasoning. 2. W hich combination of variables will pick up the fewest staples? Why do you think this will be so? Hypotheses will vary and should be supported by logical reasoning. Collect Data Test 1: Number of staples picked up when connected to one battery Electromagnet description 5 cm nail with 10 coils 10 cm nail with 10 coils 5 cm nail with 20 coils 10 cm nail with 20 coils Trial 1 Trial 2 Trial 3 Results will vary, depending on the materials used. The number of staples listed under each trial may vary within each row but should be similar. In Test 1 (one battery), the combination of variables that picks up the greatest number of staples is likely to be the 10 cm nail with 20 coils. Average Each response should accurately calculate the average of Trials 1, 2, and 3 on each row. Test 2: Number of staples picked up when connected to two batteries Electromagnet description 5 cm nail with 10 coils 10 cm nail with 10 coils 5 cm nail with 20 coils 10 cm nail with 20 coils © Learning A–Z All rights reserved. © Learning A–Z All rights reserved. Trial 1 Trial 2 Trial 3 Results will vary, depending on the materials used and how well the batteries are connected. The number of staples listed under each trial may vary within each row but should be similar. In Test 2 (two batteries), the combination of variables that picks up the greatest number of staples should, in theory, be the 10 cm nail with 20 coils because greater current should yield a stronger electromagnet. But in practice, results may vary. 4 Average Each response should accurately calculate the average of Trials 1, 2, and 3 on each row. www.sciencea-z.com 3 www.sciencea-z.com experiment Electricity and Magnetism—Electromagnets Questions Answer key and explanations Analyze Data 1. W hen your results were averaged, which combination of three variables made your electromagnet pick up the most staples? Results will vary but should accurately reflect an analysis of the recorded data. 2. W hen your results were averaged, which combination of three variables made your electromagnet pick up the fewest staples? Results will vary but should accurately reflect an analysis of the recorded data. 3. W hich variable affected the results most—nail length, number of coils, or number of batteries? Why do you think this variable was so important? Results will vary but should accurately reflect an analysis of the recorded data. The number of coils may affect the results most. When more coils are added around the core of the electromagnet, more electrons in the nail are polarized, resulting in a stronger magnet. The number of batteries might have an even greater impact on the results, but the flow of current from one battery to the next can be affected by how well they are held together during Test 2. 4. W hich variable affected the results least—nail length, number of coils, or number of batteries? Why do you think this variable was not as important as the others? Results will vary but should accurately reflect an analysis of the recorded data. Nail length may affect the results least. The number of coils and number of batteries have a greater impact on the amount of electric current passing through the nail, resulting in a stronger magnet. 5. W hy was it important to conduct three trials with each electromagnet and find the average results? Ideally, at least three trials should be conducted in a science investigation to ensure that results are reliable. More trials reduce the chances of drawing conclusions based on quirks and errors, and increase the potential accuracy of measurement. © Learning A–Z All rights reserved. 4 www.sciencea-z.com experiment Electricity and Magnetism—Electromagnets Questions answer key and explanations Draw Conclusions 1. W ould the electromagnets have worked if you had used a piece of wood or plastic instead of a nail? Why or why not? The electromagnets would not have worked. A ferrous metal—such as iron, cobalt, or nickel— must be used to allow electric current to create a magnetic field around the core material. 2. W hy did the safety tips suggest disconnecting just one wire from the battery instead of both wires? The electromagnet has a current running through it only when both wires are connected. Disconnecting just one wire breaks the circuit and stops the flow of electricity, so disconnecting both wires is not necessary. 3. H ow would you build an electromagnet that was stronger than any of the ones you used in this activity? Answers will vary but may include: use stronger batteries, use more batteries, wrap the coil around the nail more times, use a longer nail, use a thicker nail, or use a thinner nail. (These responses may be a good starting point for further inquiry into building electromagnets. However, always monitor the introduction of new variables for safety!) © Learning A–Z All rights reserved. 5 www.sciencea-z.com