merlot 2007 august 9, 2007 physics 8.02: faraday’s law john belcher this presentation is online...
TRANSCRIPT
MERLOT 2007 August 9, 2007
Physics 8.02: Faraday’s Law
John Belcher
This presentation is online now at
http://web.mit.edu/viz/MERLOT/
MERLOT 2007 August 9, 2007
The MIT TEAL Simulations and Visualizations for
Faraday’s Law
John W. Belcher
Kavli Center for Astrophysics and Space Research
MIT Department of Physics
MERLOT 2007 August 9, 2007
Funding Sources
NSF CCLI DUE-0618558Davis Educational Foundation
d’Arbeloff Fund for Excellence in MIT Education
iCampus, the MIT/Microsoft AllianceHelena Foundation
MIT Classes of 51, 55, 60
MERLOT 2007 August 9, 2007
Credits for TEAL Visualizations:
Project Manager: Andrew McKinney Java Simulations: Andrew McKinney, Philip Bailey,
Pierre Poignant, Ying Cao, Ralph Rabat, Michael Danziger
3D Illustration/Animation: Mark Bessette, Michael Danziger
ShockWave Visualizations: Michael DanzigerVisualization Techniques R&D: Andreas Sundquist
(DLIC), Mesrob Ohannessian (IDRAW)
These visualizations were developed in the context of TEAL, a much larger freshman physics reform project at MIT for interactive studio physics
MERLOT 2007 August 9, 2007
My Career Before VisualizationPI on the Voyager Plasma Science Instrument on the Voyager Spacecraft
I have spent a lot of time trying to explain the unseen to reporters at Voyager press conferences since 1979
I have taught E&M at all levels at MIT for 35 years
I spent 6 years helping change freshman E&M to an interactive format
Neptune’s Magnetosphere 1989
Going to Jupiter Saturn Uranus and Neptune is easy
Reforming introductory physics is hard
MERLOT 2007 August 9, 2007
TEAL: Technology Enabled Active Learning
Large freshman physics courses have inherent problems
Lecture/recitations are passive
No labs (at MIT) leads to lack of physical intuition
Math is abstract, hard to visualize (esp. E&M)
TEAL/Studio addresses these by
Replacing large lectures with interactive, collaborative pedagogy
Incorporating desk top experiments
Incorporating visualization/simulations to make the unseen seen
MERLOT 2007 August 9, 2007
Outline of TalkWhat do we mean by the concept of fields?
Why is the field concept hard to understand?
Examples of Faraday’s Law experiments
How do visualizations help in understanding these experiments?
Examples of Visualizations
How Does This Contribute to E&M Understanding?
MERLOT 2007 August 9, 2007
What do we mean by the concept of fields?
Electromagnetic fields are invisible stresses that exist at every point in space
They are generated by the electric charge carried by material objects
All everyday interactions between material objects are mediated by the electromagnetic fields they produce
Material objects never touch—instead, their fields interact, giving the illusion of “touching”
MERLOT 2007 August 9, 2007
The illusion of touchYou are convinced that your hand reaches out and touches the hand of a loved one, because that is the way you have learned to internalize reality…
…in reality the matter in your hand generates electromagnetic fields that surround your hand …
…and when you put your hand near the hand of a loved one the fields in their hand set up a repulsion…
…that keeps the matter in your hand from interpenetrating the matter in their hand…
…and you interpret that repulsion as your hand having touched the hand of your loved one …
…even though the matter in your hand never touches your loved one’s hand…
…or anything else for that matter…
MERLOT 2007 August 9, 2007
The illusion of touchOf course I don’t really believe this, even though I know it is true
Why don’t I believe this?
MERLOT 2007 August 9, 2007
MERLOT 2007 August 9, 2007
Why is the field concept hard to understand?
Fields are invisible
Our experience with them is indirect—other than playing with magnets and experiencing the effects of static electricity, we have no intuition about them
The theory that describes them is very mathematical
How do we make the idea of fields more accessible?
Make visible representations of them!
MERLOT 2007 August 9, 2007
Examples of Faraday’s Law experiments: I
Magnet and a coil. Moving magnet induces a current in a stationary coil. The coil has no source of power, but a current flows in the coil when I move a magnet near it.
Where does the energycome from to make the current in the coil flow?
MERLOT 2007 August 9, 2007
Examples of Faraday’s Law experiments: I
MERLOT 2007 August 9, 2007
Examples of Faraday’s Law experiments: I
This looks magical!
Why? Because we don’t see the intervening agent that links the magnet and the coil—the field!
So lets show the field:
MERLOT 2007 August 9, 2007
Examples of Faraday’s Law experiments: I
MERLOT 2007 August 9, 2007
Examples of Faraday’s Law experiments: I
MERLOT 2007 August 9, 2007
Examples of Faraday’s Law experiments: II
Magnet falling through a non-magnetic conducting ring—e.g. one made of copper.
MERLOT 2007 August 9, 2007
Falling Magnet
MERLOT 2007 August 9, 2007
Falling Magnet
MERLOT 2007 August 9, 2007
How do visualizations help in understanding fields?
In visualizations we can make the fields visible
The dynamical effects of fields can be understood by analogy with rubber bands and strings
This insight is due to Faraday, the father of the concept of fields
Making the fields visible and animated and using the analogy of rubber bands and strings gives insight into the reasons that fields have the effects they do
MERLOT 2007 August 9, 2007
Examples of Interactive Visualizations
Moving a wire coil past a stationary magnet
We do this experiment in class and then we look at a virtual interactive representation of it.
MERLOT 2007 August 9, 2007
Loop of wire has inductance L and
resistance R and a decay time of L/R
MERLOT 2007 August 9, 2007
• Do or show a real experiment • Build a virtual model of the real
experiment• Add field representation• Show the field three ways:
•Vector Field Grid•Field Lines •Line Integral Convolution
Guiding Principles
MERLOT 2007 August 9, 2007
Moving Field LinesHelps with higher order concepts, most obviously the
flow of electromagnetic energy, but also the flow of electromagnetic momentum and the stresses transmitted by fields, that is, the Maxwell Stress Tensor
Fields transmit a pressure perpendicular to themselves and a tension parallel to themselves—that is you can intuit their dynamical effects by looking at their shape!
0 S
emmech dVdt
ddATPP
�
IBBIEET
���22
2
11
2
1BE
oo
MERLOT 2007 August 9, 2007
How Much Does This Contribute to E&M Understanding?
1.No clear evidence they are useful in the way we have been using them in TEAL
2.Need to embed these visualizations into a “Guided Inquiry” framework
3.Need more than just accessibility and exploration and “gee whiz”
4.I currently have an NSF Grant to do just this
MERLOT 2007 August 9, 2007
All of these visualizations and many more are located
at
http://web.mit.edu/8.02t/www/802TEAL3D/
MERLOT 2007 August 9, 2007
Applications and software are open source, but not well
documented
We are working on the documentation
http://web.mit.edu/viz/soft/
MERLOT 2007 August 9, 2007
Oscillating Electric Dipole
4
ˆ)ˆ(
4
)ˆ(ˆ3
4
)ˆ(ˆ3),(
223 rcrcrt
ooo nxnxppnpnpnpn
rE
MERLOT 2007 August 9, 2007
DLIC: Turning On An Electric Dipole
4
ˆ)ˆ(
4
)ˆ(ˆ3
4
)ˆ(ˆ3),(
223 rcrcrt
ooo nxnxppnpnpnpn
rE
MERLOT 2007 August 9, 2007
DLIC: Light charges around heavy charge
The Seen Versus The Unseen
Link to 10 Meg AviLink to 1 Meg Avi
MERLOT 2007 August 9, 2007
Two Other Visualizations
Electrostatic Video Game Interactive
MERLOT 2007 August 9, 2007