# Interactive animations of

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16 Νοε 2013 (πριν από 4 χρόνια και 5 μήνες)

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Interactive animations of
electromagnetic waves

András Szilágyi

Institute of Enzymology,

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

-
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?

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"

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