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 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 Plane-polarized light

Right circular Left circular Circularly polarized light

Interaction of light and matter: Absorption 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

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

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

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

Web Tutorial 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 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 s 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