1 How can we produce electricity from magnetism? Robert H. Winston Thomas A. Edison High School 2009 August 5, 2009

Thursday, September 17, 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 90 o. 4.Why do we use directional compass? 5.Why does the compass needle rotate 90 o ? 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 - )?)

Thursday, September 17, So electricity can produce magnetism. However, can we produce electricity from magnetism? So, what’s the answer? But, “How can we induce a conventional current using magnetism?”

Thursday, September 17, The flow of electric charge from the positive (+) terminal of a battery to the negative (-) terminal of the battery is called conventional current.  Electricity is the flow of charges around a circuit carrying energy from the battery (or power supply) to components such as lamps and motors 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

Thursday, September 17, Review Right Hand Screw Rule 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).

Thursday, September 17, 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.

Thursday, September 17, Main Demonstration—Group Work (4) Introduction 1 o Coil 2 o Coil Digital Multimeter Iron or Iron Nickel Core Switch Voltage Source 6.0 Volts

Thursday, September 17, Figure-Electromagnetic Induction Figure-AFigure-A stepdown transformer Electromagnetic induction  Induction Coils  Transformers

Thursday, September 17, 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 1 o 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 1 o coil when the switch is turned on and off? 3. What happens to the multimeter in the circuit with the 2 o coil when the current in the 1 o circuit is flowing? 4. …when it stops flowing? Why? 5.Why is likely that when the magnetic field expands or grows around the 1 o coil it is also expands or grows around the 2 o 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 1 o coil circuit differ from the current in the 2 o coil circuit?” 8. How does the presence of a whole core affect everything?

Thursday, September 17, When nothing seems to work right, then simulate. Figure-A stepdown transformer Figure-Phet simulation encompassing : (1) Bar Magnets; (2) Pick Up Coil; (3) Electromagnetic Induction; (4)Transformers; (5) Generators

Thursday, September 17, 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 1 o 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 1 o coil when the switch is turned on and off? 3. What happens to the multimeter in the circuit with the 2 o coil when the current in the 1 o circuit is flowing? 4. …when it stops flowing? Why? 5.Why is likely that when the magnetic field expands or grows around the 1 o coil it is also expands or grows around the 2 o 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 1 o coil circuit differ from the current in the 2 o coil circuit?” 8. How does the presence of a whole core affect everything?

Thursday, September 17, (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? (d) How do you think the presence of a commutator a affects the output of the current? Think Pair Share-Physlet Diagram of a generator from Physlet simulation Effect of a commutator on an electrical circuit.

Thursday, September 17, Closure: So… how can we explain what happened with the Cu tube demonstration? Why did the magnets fall so slowly in comparison to the non-magnets? The physics of Lenz’s law

Thursday, September 17, Rob Winston’s first day in the Northeastern Lab

Thursday, September 17, Acknowledgements Claire J. Duggan, Center for STEM Education & Program Director of the 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 Northeastern University Physics Northeastern University Northeastern University National Science Foundation With much appreciation and thanks! RHW