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How can we produce electricity from magnetism?
Robert H. Winston
Thomas A. Edison High School
RET @NEU 2009
August 5, 2009
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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-)?)
Monday, May 22, 2017
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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?”
Monday, May 22, 2017
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Electricity is the flow of charges around a circuit carrying energy from
the battery (or power supply) to components such as lamps and motors
Click image to link
The flow of electric charge from the positive (+) terminal of a battery
to the negative (-) terminal of the battery is called conventional
current.

Click image to link
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
Click image to link
Monday, May 22, 2017
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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
Monday, May 22, 2017
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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)?
Click image to link
Describe the ways in which this is different from
Oersted’s Effect.
Monday, May 22, 2017
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Main Demonstration—Group Work (4)
Introduction
Iron or
Iron
Nickel
Core
Digital
Multimeter
1o Coil
Coil
22oo Coil
Switch
6.0
Voltage
Source
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Volts
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Electromagnetic inductionInduction CoilsTransformers
Figure-Electromagnetic Induction
Monday, May 22, 2017
Figure-A stepdown transformer
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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?
Monday, May 22, 2017
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When nothing seems to work right, then simulate.
Click image to link
Figure-Phet simulation encompassing :
(1) Bar Magnets; (2) Pick Up Coil;
(3) Electromagnetic Induction;
(4)Transformers; (5) Generators
Figure-A stepdown transformer
Click image to link
Monday, May 22, 2017
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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?
Monday, May 22, 2017
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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
Click image to link
(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.
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Closure:
So… how can we explain what happened with the Cu tube demonstration?
The physics of Lenz’s law
Click image to link
Click image to link
Why did the magnets fall so slowly in comparison to the non-magnets?
Monday, May 22, 2017
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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!
Monday, May 22, 2017
RHW
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