MERLOT 2007 August 9, 2007 Physics 8.02: Faraday’s Law John Belcher This presentation is online now at

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 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

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!

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 802TEAL3D/

MERLOT 2007 August 9, 2007 Applications and software are open source, but not well documented We are working on the documentation

MERLOT 2007 August 9, 2007 Oscillating Electric Dipole

MERLOT 2007 August 9, 2007 DLIC: Turning On An Electric Dipole

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