レーザー光を用いた水の吸光度の測定 : 水の青色を考える実験教材

抄録

The mechanisms of how materials are colored are not mentioned in high school science programs, even though colors or changes of colors are very useful in science as indicators of chemical reactions or the presence of chemical substances, for example, litmus papers and starch-iodine titrations. The primary question, 'Why is water blue?', has never been answered in science textbooks for high school. The color of a transparent material is shown as the complementary color of absorbed light in the material. Therefore water absorbs red colored light more than green and blue ones. I developed a new device which can measure optical absorbance of pure water by using red and green laser pointers as light sources and a solar battery as a sensor. The performance of this device shows the following : 1. Red colored light is clearly more absorbed in pure water than green colored light. 2. An absorbance coefficient of red colored light could be calculated as 3.5×10-3, which is almost the same as the previously known figure (E.O. Hulburt, 1945). Laser pointers have become inexpensive and several other colors are being developed. This device which uses these light sources, is expected to be utilized for school experiments.