Excitation of light (Dillon Lopez)

Title: Triboluminescence and Fluorescence of Wintergreen

Principle(s) Investigated: Atomic absorption, excitation of electrons, and fluorescence

Standards: HS-PS4-1: Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media.

HS-PS4-4 Evaluate the validity and reliability of claims in published materials of the effects that different frequencies of electromagnetic radiation have when absorbed by matter.

Materials: Wintergreen LifeSaver mints, peppermint LifeSaver mints, a hammer, and a dark classroom or dark area.

Procedure:

1. Put everyone in pairs of two.

2. Give each pair two wintergreen mints and two peppermint mints.

3. Instruct each pair to chew very hard on the mints (one at a time) with their mouth open so the other person can see.

3b. If no one sees the spark, take each mint and smash them with a hammer to display the phenomenon.

4. Instruct them to write down their observations.

5. Discuss with class why the wintergreen mints sparked and the peppermint did not. (Give them a hint as to how light is emitted when energy is absorbed by a molecule.

Student prior knowledge: The students must have prior knowledge of the properties of waves, the relation frequency and wavelength have on energy, and electromagnetic spectrum.

Explanation: In this experiment the students will see the wintergreen mints spark while the peppermint mints do not spark. This is caused by triboluminescence, the process by which physical forces causes the emission of an electron. This emitted electron will collide with the nitrogen molecules in the air, overall giving them energy. When this energy is absorbed by nitrogen its electrons will go from a ground state to an excited state. When the electrons fall back down from their excited state, a photon is emitted. This happens in every crystalline sugar but the light emitted is within the UV range of the electromagnetic spectrum so our eyes cannot see it.

However the wintergreen molecule, methyl salicylate, is fluorescent. Fluorescence is when a molecule absorbs light energy (E = hv) and emits the light at a longer wavelength than it absorbed due to the molecule absorbing some of the energy. Remember there is a mathematical relationship between light energy (E = hv) and the wavelength (c = λv), this can be rearranged as E = ch/λ. Ignoring the constants of speed of light (c) and Planck's constant (h) we can see an inversely proportional relationship between wavelength (λ) and energy.

Since the wintergreen molecules are absorbing the light energy given off by the nitrogen molecules, the energy difference is now lower. A lower energy difference means the wavelength of light given off is now larger and it just so happens to put this wavelength within the visible light spectrum.

Questions & Answers:

1. Why does the peppermint mint not spark?

It does not spark because the peppermint molecule is not fluorescent therefore the light given off is still within the UV spectrum and our eyes cannot see it.

2. What is the original source of energy that we put into the system?

The physical chewing of the candy is the addition of the energy towards the system.

3. If we were to chew harder or hit the peppermint molecule with a giant hammer would we see light?

No, there are two reasons why this would not happen. The first being, energy and wavelength are inversely proportional, so if we add more energy to the system than the wavelength emitted would technically get smaller and be further up on the electromagnetic spectrum. The second is because the emission of light is quantized, therefore there are discrete energy differences between each shell of an atom. Due to peppermint never fluorescing the electrons will always go back to their ground state and the energy difference will always be the same amount.

Applications to Everyday Life:

1. We see the excitation of light in our everyday lives when we drive throughout the streets at night. Many cities use sodium lamps which give off a yellowish color but you may notice cities in other states have white street lights due to their usage of LED light bulbs instead.

2. Fireworks! Whenever we go see a firework show we see many different colors illuminating the sky. This is due to the various elements that they put into the fireworks. Each element gives off different spectral lines meaning each element will absorb and emit light at different wavelengths. This allows us to see all the different amounts of colors within those fireworks.

3. We see fluorescence used in crime scenes! If you have ever watched CSI then you probably see them use UV lights to illuminate dried up blood from a crime scene. This works because the crime scene is previously sprayed with luminol, a very fluorescent molecule, this molecule will bind to blood and when UV light is shined upon it, it will glow.

Photographs: Include photos and diagrams that illustrate the how the investigation is performed.

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Videos: Cool slow motion video Life Saver Spark

IMPORTANT NOTE: Embed a Youtube Video that illustrates the procedure and results. This video should reside in your YouTube account and should be viewable by all. You may use a video in another persons YouTube channel if the video is better quality than what you can make.