merlot 2007 august 9, 2007 physics 8.02: faraday’s law john belcher this presentation is online...

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