Physics for the first date --- wintergreen flashes
Jearl Walker www.flyingcircusofphysics.com
September 2014 You and a friend first adapt your eyes to darkness for about 15 minutes in a closet or outside on a moonless night. Then have your friend chew a wintergreen LifeSaver candy (a candy in the shape of a marine lifesaver and infused with the oil of wintergreen) with the mouth as open as possible so that you can see inside. Why does each bite initially produce a faint flash of blue light, and why do later bites fail to produce the light? (If you don’t want to eat the candy, squeeze it with a pair of pliers until it fractures.) Recording the brief, faint emissions of light with a camera is tricky but here is a video that is pretty good.
Whenever a bite breaks one of the mint’s sugar crystals into pieces, the pieces will probably end up with different charges. Suppose a crystal breaks into pieces A and B, with A negatively charged and B positively charged.
Some of the electrons on A will then jump across the gap to reach B. Because air has moved into the gap after the crystal breaks, these electrons jump through air. Those that collide with nitrogen molecules in the air transfer energy to the molecules, exciting them. When the molecules de-excite, they emit in the ultraviolet range, which you cannot see. However, the wintergreen molecules on the surface of the candy pieces absorb ultraviolet light and then emit blue light, which you can see—it is the blue light coming from your friend’s mouth. This process of absorbing light in one wavelength range (here, in the ultraviolet) and then emitting light in a longer wavelength range (here, blue light) is called fluorescence, and the process of producing light by fracturing crystals is called triboluminesce. In this next video, sugar crystals are continuously crushed in a high-speed blender. When shot from overhead by a low-light camera, you see a luminous ring in the blender. As the larger crystals are broken up into smaller crystals, the light gradually fades.
Dots · through ··· indicate level of difficulty
Journal reference style: author, journal, volume, pages (date)
Book reference style: author, title, publisher, date, pages
· Harvey, A History of Luminescence, American Philosophical Society (Philadelphia, Pennsylvania), 1957, Chapter 10
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