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How can we produce electricity from magnetism?
Robert H. WinstonThomas A. Edison High SchoolRET @NEU 2009August 5, 2009
Friday, April 21, 2023 2
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 thatconductor.
(Why is it defined in terms of charges rather than electrons (e-)?)
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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?”
http://www.grand-illusions.com/acatalog/lenzs_law.jpg
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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
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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).
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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.
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Main Demonstration—Group Work (4)
Introduction
1o Coil 2o Coil2o Coil
Digital Multimeter
Iron or Iron Nickel Core
Switch
Voltage Source
6.0
Volts
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Figure-Electromagnetic InductionFigure-A stepdown transformer
Electromagnetic inductionInduction CoilsTransformers
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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?
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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
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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?
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(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 partsin 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 thecurrent?
Think Pair Share-Physlet
Diagram of a generator from Physlet simulation
Effect of a commutator on an electrical circuit.
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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
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Rob Winston’s first day in the Northeastern Lab
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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!
RHW
