Transcript Slide 1
How can we produce electricity from magnetism? Robert H. Winston Thomas A. Edison High School RET @NEU 2009 August 5, 2009 1 1. Turn the directional compass so that its needle is parallel to the wire. 2. Close the switch to allow the current to flow through the wire for about 5-10 s. 3. The compass needle now rotates 90o. 4. Why do we use directional compass? 5. Why does the compass needle rotate 90o? This phenomenon is known as the Oersted Effect A flow of charges through a conductor will induce a magnetic field around that conductor. (Why is it defined in terms of charges rather than electrons (e-)?) Tuesday, July 21, 2015 2 So electricity can produce magnetism. However, can we produce electricity from magnetism? http://www.grand-illusions.com/acatalog/lenzs_law.jpg So, what’s the answer? But, “How can we induce a conventional current using magnetism?” Tuesday, July 21, 2015 3 Electricity is the flow of charges around a circuit carrying energy from the battery (or power supply) to components such as lamps and motors The flow of electric charge from the positive (+) terminal of a battery to the negative (-) terminal of the battery is called conventional current. Positive charges flowing forwards are equivalent to negative charges flowing backwards. The forward motion is conventional Current while the backward motion is simply electric current Tuesday, July 21, 2015 4 Review According to Ampere's law, current (represented by yellow) running in the z direction is causing a B field in the - θ direction (represented by purple). Right Hand Screw Rule Tuesday, July 21, 2015 5 Think Pair Share—Consult with your neighbor for each of the following: (a) Write down what you observe (b) What happens when the magnet moves in and out of the coil? (c) Why does the galvanometer needle move back-and-forth (passing through zero)? Describe the ways in which this is different from Oersted’s Effect. Tuesday, July 21, 2015 6 Main Demonstration—Group Work (4) Introduction Iron or Iron Nickel Core Digital Multimeter 1o Coil Coil 22oo Coil Switch 6.0 Voltage Source Tuesday, July 21, 2015 Volts 7 Electromagnetic inductionInduction CoilsTransformers Figure-Electromagnetic Induction Tuesday, July 21, 2015 Figure-A stepdown transformer 8 Induction Coil—Check Points At some time today, someone in your group should write these down for everyone. When all is “said and done”, be sure to answer these questions. 1. There is no current in the 1o coil when the switch is off. How does that change when the switch is turned on? 2. What happens to the magnetic field around the 1o coil when the switch is turned on and off? 3. What happens to the multimeter in the circuit with the 2o coil when the current in the 1o circuit is flowing? 4. …when it stops flowing? Why? 5. Why is likely that when the magnetic field expands or grows around the 1o coil it is also expands or grows around the 2o coil? 6. How does that shape and size of the magnetic fields around the entire core change when the switch is turned off? 7. How does the current that flows in the 1o coil circuit differ from the current in the 2o coil circuit?” 8. How does the presence of a whole core affect everything? Tuesday, July 21, 2015 9 When nothing seems to work right, then simulate. Figure-Phet simulation encompassing : (1) Bar Magnets; (2) Pick Up Coil; (3) Electromagnetic Induction; (4)Transformers; (5) Generators Figure-A stepdown transformer Tuesday, July 21, 2015 10 Induction Coil—Redux At some time today, someone in your group should write these down for everyone. When all is “said and done”, be sure to answer these questions. 1. There is no current in the 1o coil when the switch is off. How does that change when the switch is turned on? 2. What happens to the magnetic field around the 1o coil when the switch is turned on and off? 3. What happens to the multimeter in the circuit with the 2o coil when the current in the 1o circuit is flowing? 4. …when it stops flowing? Why? 5. Why is likely that when the magnetic field expands or grows around the 1o coil it is also expands or grows around the 2o coil? 6. How does that shape and size of the magnetic fields around the entire core change when the switch is turned off? 7. How does the current that flows in the 1o coil circuit differ from the current in the 2o coil circuit?” 8. How does the presence of a whole core affect everything? Tuesday, July 21, 2015 11 Think Pair Share-Physlet (a) What device is shown on the right? Why is it given that particular name? (b) Why might Michael Faraday or Joseph Henry have marveled at the design of a generator? (c) How are the movements of the parts in a generator different from the movements of the parts of a transformer? Diagram of a generator from Physlet simulation (d) How do you think the presence of a commutator a affects the output of the current? Effect of a commutator on an electrical circuit. Tuesday, July 21, 2015 12 Closure: So… how can we explain what happened with the Cu tube demonstration? The physics of Lenz’s law Why did the magnets fall so slowly in comparison to the non-magnets? Tuesday, July 21, 2015 13 Rob Winston’s first day in the Northeastern Lab Tuesday, July 21, 2015 14 Acknowledgements • Claire J. Duggan, Center for STEM Education & Program Director of the RET @ Northeastern University • Rocco Cieri, Medford Public Schools • Matthew Corcoran, Science Department Chairperson—Framingham High School • Professor Nian X. Sun, Electrical and Computer Engineering Department • Ming Liu, Ph.D. Candidate, Northeastern University • Yunume Obi „ „ „ „ • Xing Xing „ „ „ „ • Electrical and Computer Engineering Department @ Northeastern University • Physics Department @ Northeastern University • Northeastern University • National Science Foundation With much appreciation and thanks! Tuesday, July 21, 2015 RHW 15