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I went to the Center of Science and Industry (COSI) and saw and exhibit called shadow pictures. It is where you stand in front of this "screen-like board" and a bright light flashes behind you and when you move, your shadow stays. What is the "screen-like board" made of?
Thank you very much,
- Amanda Jameson (age 10)
Miami Valley School, Centerville, OH,USA
The shadow board you saw was probably made of the same
kind of "glow in the dark" material that some of your toys might also
be made of. You may at some time have played with a ball that glowed a
light yellowish-green color if you took it into a dark room after
holding it up to a light for a while.
Materials that behave
in this way have the very interesting property that they absorb energy
(the light you expose it to) very easily but have a much harder time
releasing this energy (the light you see). This means that it takes a
much longer time to release the light than it took to absorb it, which
means that the stuff might "glow" for quite a while (although not very
brightly) after you hold it up to a light for only a short time.
the science center the screen you stood in front of what probably made
if this kind of material. The very bright flash of light was absorbed
by the screen wherever you were not "in the way". After the flash the
screen glowed for several seconds, except where your shadow had been
(since this part of the screen was never exposed to the flash to begin
(republished on 07/28/06)
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