Background
This experiment is meant to go along with our unit on heat. It would be good to have a look at my lesson on the electromagnetic spectrum to get an understanding of how light interacts with the electrons in atoms. The aim of this experiment is to determine if glow-in-the-dark toys react differently to heat than glow sticks. Everything about the experiment is written up in the power point file below. You can also discuss ways that the test is fair or not. Did you use the same type of glow stick in each condition, did you activate them at the same time, and did you observe them under the same lighting conditions each day, for example.
Materials and Methods
Ask the kids to choose the null hypothesis (no difference) or the alternative. Ask them why they chose that, but don’t make any judgment about it. Ask if they have any observations about these items. Most of the kids will know that the glow stick needs to be activated by bending it and that the toys need to be exposed to light to work. Have them check to see if all the items glow in the dark and then put the objects in their different environments. Make sure you label each item with their location so that you don’t confuse them when making your daily observations. Have the students record their data in a chart like the one in the power point file.
Results and Explanation
The glow-in-the-dark toys are not affected by heat. They just need to charge in the sun. When exposed to light the electrons raise to a higher level. That energy is released slowly as visible light and that is why the item glows. This is why you can keep recharging them, and they will glow. This is called phosphorescence.
Glow sticks glow due to a chemical reaction. Inside the stick there are two different liquid chemicals. When you bend them you break a glass vial inside, and the two chemicals mix. This starts the chemical reaction. An intermediate product of this reaction has an excited electron. An excited electron is one that has been raised to a higher energy level. This electron falls back down to a lower energy level and releases visible light as it does this. This is called chemiluminescence. Once the chemicals run out, the reaction stops and light is no longer released. Heat will increase the rate of this chemical reaction and removing heat will slow the reaction down. The glow stick in the freezer should take them longest amount of time to stop glowing.
These are not to be confused with fluorescence. Fluorescence occurs when some items are exposed to UV light (a black light). The UV light is absorbed by the object and this excites an electron. When that electron falls back down to a lower energy level, it releases energy with a longer wavelength (visible light). This item will always glow under a black light, but as soon as the light is turned off the item will stop glowing.
*I would recommend thick glow sticks for this instead of the bracelet type. You should also have a very dark room, or have a few kids take the glow sticks home to check at night.*
If you want to do a one day experiment you can use effervescent tablets and see how they dissolve faster in warm water than in cold water. I found a great experiment about how the surface area of the tablets affects the rate that they dissolve in water. I wrote up the two experiments together in this file.
For more STEAM ideas, click on the STEAM tab on this website, or take a look at my Pinterest board.