Interactive animations of

clappergappawpawΠολεοδομικά Έργα

16 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

57 εμφανίσεις

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

)
/
sin(
t
x
A
E
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.

GNUPLOT
:
equation
plotting
program

Vertical

Horizontal

)
/
sin(
t
x
A
E
y




Plane
-
polarized light

)
/
sin(
t
x
A
E
z




Right circular

Left circular

Circularly polarized light

)
90
/
sin(




t
x
A
E
y


)
/
sin(
t
x
A
E
z




)
90
/
sin(




t
x
A
E
y


)
/
sin(
t
x
A
E
z




Interaction of light and matter: Absorption

)
/
sin(
t
x
Ae
E
x
y






Material with an
extinction
coefficient



The light gets weaker (its amplitude
drops)

In Out

Interaction of light and matter: Refraction

In Out

Material with an
index of
refraction

n

The light slows down inside the
material, therefore its wavelength
becomes shorter and its phase gets
shifted

)
/
sin(
t
nx
A
E
y




Circular dichroism

In Out

Material having different
extinction coefficients for
right and left circularly
polarized lights:

R

and

L

Plane
-
polarized light becomes
elliptically polar

)
90
/
sin(
)
90
/
sin(










t
x
Ae
t
x
Ae
E
x
x
y
L
R






)
/
sin(
)
/
sin(
t
x
Ae
t
x
Ae
E
x
x
z
L
R












Circular bi
-
refringence

In Out

Material having different
refraction indices for right
and left circularly polarized
lights:
n
R

and
n
L

The plane of polarization of plane
-
polarized light gets rotated

)
90
/
sin(
)
90
/
sin(
L
R








t
x
n
A
t
x
n
A
E
y




)
/
sin(
)
/
sin(
R
t
x
n
A
t
x
n
A
E
L
z








Circular dichroism AND bi
-
refringence

In Out

Material having different
extincion coefficients AND
refraction indices for right
and left circularly polarized
lights:

R

and

L

AND
n
R

and
n
L

Plane polarized light gets elliptically
polar, with the great axis of the ellipse
being rotated relative to the original
plane of polarization

)
90
/
sin(
)
90
/
sin(
L
R










t
x
n
Ae
t
x
n
Ae
E
x
x
y
L
R






)
/
sin(
)
/
sin(
L
R
t
x
n
Ae
t
x
n
Ae
E
x
x
z
L
R












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


45
º 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 CD
-
ROMs:


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