Transcript Interactive animations of electromagnetic waves

Interactive animations of
electromagnetic waves
András Szilágyi
Institute of Enzymology,
Hungarian Academy of Sciences
Electromagnetism
Maxwell’s equations describe
electromagnetic waves but they are hard
to grasp intuitively.
In our minds, most of us just have vague
images of E and B vectors oscillating
somewhere in space.
If we ourselves do not really understand
electromagnetic waves, how can we
teach them effectively?
Teaching circular dichroism?
Important method in biological spectroscopy. CD spectra tell us a great deal of
information about the structure of proteins.
Textbook figures on circular dichroism do not really help understand what is
happening
Animation makes it clear
GNUPLOT:
equation
plotting
program
E
A
sin(
x
/


t)
y
Vertically (y axis) polarized wave having an amplitude A, a wavelength of and an
angular velocity (frequency * 2) of , propagating along the x axis.
Plane-polarized light
Vertical
E
A
sin(
x
/


t)
y
Horizontal
E
A
sin(
x
/


t)
z
Circularly polarized light
Right circular
E
A
sin(
x
/


t
90

)
y
E
A
sin(
x
/


t)
z
Left circular
E
A
sin(
x
/


t
90

)
y
E
A
sin(
x
/


t)
z
Interaction of light and matter: Absorption
Material with an extinction
coefficient 
The light gets weaker (its amplitude
drops)


x
E

Ae
sin(t
x
/


)
y
In
Out
Interaction of light and matter: Refraction
Material with an index of
refraction n
The light slows down inside the
material, therefore its wavelength
becomes shorter and its phase gets
shifted
E
A
sin(
nx
/


t)
y
In
Out
Circular dichroism
Material having different
extinction coefficients for
right and left circularly
polarized lights: R and L
Plane-polarized light becomes
elliptically polar







x


x
R
L
E

Ae
sin(
x
/

t

90

)

Ae
sin(
x
/

t

90

)
y
In


Out



x


x
R
L
E

Ae
sin(
x
/

t
)

Ae
sin(
x
/
t
)
z
Circular bi-refringence
Material having different
refraction indices for right
and left circularly polarized
lights: nR and nL
The plane of polarization of planepolarized light gets rotated


In


Out
E

A
sin(
n
x
/

t

90

)

A
sin(
n
x
/

t

90

)
y
R
L




E

A
sin(
n
x
/
t
)

A
sin(
n
x
/
t
)
z
R
L
Circular dichroism AND bi-refringence
Material having different
extincion coefficients AND
refraction indices for right
and left circularly polarized
lights: R and L AND nR
and nL
Plane polarized light gets elliptically
polar, with the great axis of the ellipse
being rotated relative to the original
plane of polarization








In
Out

x

x
R
L
E

Ae
sin(
n
x
/

t

90

)

Ae
sin(
n
x
/

t

9

)
y
R
L





x

x
R
L
E

Ae
sin(
n
x
/

t
)

Ae
sin(
n
x
/

t
)
z
R
L
Web Tutorial
http://www.enzim.hu/~szia/cddemo/edemo0.htm
• I. Basic concepts: Electromagnetic waves and types of polarization
• Plane-polarized wave: Horizontal
• Plane-polarized wave: Vertical
• Superposition of plane-polarized waves: Horizontal + Vertical  45º Plane
• Superposition of plane-polarized waves: Horizontal + Vertical  Right circular
• Superposition of plane-polarized waves: Horizontal + Vertical  Left circular
• Circularly polarized waves: Right and Left
• Superposition of circularly polarized waves: Right + Left circular  Plane!
• II. Interaction of light and matter
• Plane-polarized wave: Absorption
• Circularly polarized wave: Absorption
• Plane-polarized wave: Refraction
• Circularly polarized wave: Refraction
• Circular dichroism
• Circular birefringence
• Circular dichroism AND birefringence
Disadvantages of non-interactive
animations (movies)
• Low graphic resolution, image not perfectly clear
• Tutorial is limited to a set of examples; students
cannot explore other possible scenarios
• The effect of changing one parameter or another
cannot be discovered
• Student just passively receives the information,
instead of actively discovering and exploring
phenomena
How to make it interactive?
• 3D programming is advanced stuff
• OpenGL, Java3D, etc.: very powerful but the
learning curve is a bit too long for lazy people
like me 
• Solution for lazy people: Visual Python
• Visual Python: very high level language, rapid
development
– You create objects (e.g. sphere, box, cylinder, curve,
etc.) which immediately appear and any change in
their properties is immediately rendered
– OS-independent; you can create Windows binaries
EMANIM
• http://www.enzim.hu/~szia/emanim
• Public domain software
• Source code and Windows binary
available
• In English and Hungarian
EMANIM is an application for visualizing
electromagnetic waves. Its main features are:
Live, three-dimensional presentation
Interactive rotation and zooming with the mouse
Continuous animation of wave propagation
Any or both of two waves and optionally their superposition
can be displayed
Vectors of the electric field are shown at two planes
intersecting the path of the light
Wave parameters such as type of polarization, wavelength,
amplitude and phase difference can be interactively varied
To visualize the interaction of light and matter, a piece of
material can be placed into the path of the light
Properties of this piece of material such as length, extinction
coefficients and indices of refraction can be interactively varied
User-configurable colors
EMANIM can help the user understand a wide range of
phenomena related to electromagnetic waves, from the
simplest such as a single wave in vacuum to the most
complex such as circular dichroism. Its features that promote
learning are:
19 predefined parameter sets representing important physical
phenomena
A brief explanation of each phenomenon is displayed whenever the
user selects a phenomenon from the menu
Phenomena from the following basic categories:
Types of polarization (linear, circular)
Superposition of waves
Interference of waves
Interaction of light and matter (absorption, refraction)
Light in anisotropic materials (dichroism and birefringence)
Light in optically active materials (circular dichroism and
birefringence)
Hints are displayed to suggest parameters to vary in order to gain a
better understanding of the phenomenon at hand
Five predefined views to show the phenomena from the most
optimal "camera angles"
Disadvantages of Visual Python
• Only a limited set of available objects
• Limited widget set, another GUI package
is needed for more complex GUIs
(EMANIM uses Tk)
• No way to suspend the rendering process,
therefore some jerkiness is seen in the
animations
Feedback
• Web: hundreds of views of the website per day
• Dozens of e-mails with positive feedback, many
of them from teachers who use the tutorial for
their classes
• EMANIM has been distributed on various CDROMs:
– A CD distributed to physics teachers in the UK
– A CD included with a textbook for the training wireless
network administrators
– ComputerBild Italia, a computer magazine