High School Biology-Chemistry SMILE Meeting
25 January 2005
Notes Prepared by Porter Johnson

Ben Stark [Professor of Biology, IIT]  Colors of Light
This is a mini-teach that Ben tried out last week with a fourth grade class for which he is the "science volunteer"; it seemed to go over quite well with them, and it can be adapted for the upper grades quite easily. It combines physical chemistry with physics.

He started out shining a bright flashlight through a prism and displaying the resultant rainbow on the wall.  We then discussed how reflection/transmission of some of the colors and absorption of others by various dyes/colored chemicals, leads to the property of "having a certain color." We then talked about how something that appears white does so because all the colors in the visible spectrum are reflected and none absorbed, and conversely how something which is black is so because it absorbs all the colors. This then led to the demonstration with the radiometer (also called a "light mill").

A great discussion about this apparatus can be found at the website How Does a Light Mill Work? by John Baez: http://math.ucr.edu/home/baez/physics/General/LightMill/light-mill.html. Basically, the vanes of the windmill type device inside the light mill each have a dark (light absorbing) and light (light reflecting) side and the 8 sides of the four vanes are arranged: light - dark - light - dark - ... .  The light is absorbed to a greater extent on the dark side than on the light side of each vane, and this light is converted to thermal energy which heats the air near the dark sides.  The hotter air molecules have more kinetic energy than the cooler air molecules elsewhere in the radiometer, and thus give a relatively greater push to the dark side, than to the light side, of each vane.  Thus, light shined onto the vanes of the apparatus will push the vanes in a direction in which the dark sides seem to be repelled by the light.

Ken Schug then led us in a further discussion of this interesting phenomenon. We discussed how the quantum properties of electron states leads to the absorption of the various wavelengths of light (raising the electron to a higher energy state), how the reversal of the absorption of the electron returns the electron to a lower energy state releasing either light (fluorescence) or thermal energy (what happens with the radiometer), and the photoelectric effect.

Carol Giles [Collins HS, Science] Categorization
Carol asked us to help her in the categorization of some questions for a children's science book she is writing for a class she is taking. The questions came from her students, and there were about 100 altogether!  Her tentative categories are Biological, Earth/Space Science, Mathematics, and Miscellaneous.  We suggested adding Chemistry and Physics as two additional categories.

Notes prepared by Benjamin Stark.