Materials
- Wintergreen candy (Wint-O-Green Lifesavers © work very well)
- Mirror
- Room where almost all light can be shut out
Procedure
- Enclose you and your students in a dark room and have students either face each other or hold a mirror in front of their face.
- Have the students bit down hard on a wintergreen candy, keeping their mouth open so that one can see what is happening inside. A bluish glow should be emitted from the candy.
Explanation
The candy emits a bit of light when it is crunched do to a phenomenon called triboluminescence. Materials that undergo stress by being crunched or smashed have some free electrons that get knocked loose. The electrons in turn get excited by the nearby nitrogen atoms in the air. As the nitrogen atoms get excited, the electrons jump to a different orbital in the atom. Since the electron is unstable at the higher orbital and quickly moves back down to the lowest possible orbital. As the electron jumps down it releases its energy in the form of ultraviolet light.
Most things that get crunched or smashed excite nitrogen atoms. What makes wintergreen different is that wintergreen contains methyl salicylate, part of the wintergreen flavor. This molecule is a fluorescent molecule, which means that it absorbs light at a shorter wavelength (ultraviolet) and emits light at a longer wavelength (blue light). So the ultraviolet light that the nitrogen is releasing, then excites part of the methyl salicylate molecule. As this molecule releases its energy, it shows up as the blue glow seen in your mouth.
For younger students this activity can be explained by talking about conservation of energy. The mechanical energy that the students put into the candy by biting on it is released at light energy.
Reinforcement Activities
Use the above activity to extend onto teaching your students about bright line spectra. Any easy way for students to see a bright line spectrum is by studying spectrum tubes. Using a diffraction grating, students can see the line spectrum of several different elements such as chlorine, helium, hydrogen, iodine, krypton, neon and many more.
Student can even measure the energy of different lines of spectrum by estimating the wavelength of the lines using a hand held spectroscope. This activity is great for calculations, labs, and quantitative problems.
Show students how energy can be converted from heat, light, sound, heat, electrical, etc with this all in one demonstration, clearly labeled and easy to use.
