Physics Classics Award Winner - MERLOT International Conference

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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
-
0618558

Davis Educational Foundation

d’Arbeloff Fund for Excellence in MIT
Education

iCampus, the MIT/Microsoft Alliance

Helena 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 Danziger

Visualization 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 Visualization



PI 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 Talk

What 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 touch

You 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 touch

Of 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 energy

come 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 Lines


Helps 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






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em
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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









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MERLOT 2007 August 9, 2007


DLIC: Turning On An
Electric Dipole









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MERLOT 2007 August 9, 2007


DLIC: Light charges around
heavy charge




The Seen Versus The Unseen

Link to 10 Meg Avi

Link to 1 Meg Avi

MERLOT 2007 August 9, 2007


Two Other Visualizations

Electrostatic Video Game Interactive




MERLOT 2007 August 9, 2007