1. Introduce the activity, telling students that they will explore ultraviolet wavelengths of sunlight, which are dangerous and cause skin damage.
- Survey student knowledge of ultraviolet (or UV) light and student experience with Sun damage such as sunburns and skin cancer.
- Explain that different types of light are part of the electromagnetic spectrum. UV light has a wavelength slightly shorter than visible light. Unlike visible light, we can’t see UV, but some materials react in its presence. An ingredient in tonic water, called quinine, absorbs UV and releases it, causing it to glow blue (or fluoresce). Demonstrate how tonic water fluoresces when the blacklight is turned on. Tell students that the blacklight emits UV light, not visible light, so it doesn’t look bright to us.
- Explain to students that ultraviolet light is dangerous to humans. Show students a photo of someone with a sunburn or skin cancer. Explain that people with darker skin tone are not as likely to get sunburns as people with lighter skin tone, but everyone is vulnerable to skin damage from UV radiation, no matter what their skin color.
(A) set-up with blacklight and two cups of tonic water, (B) darkened classroom with blacklight on and tonic glowing blue as quinine absorbs and then releases UV light
Credit: Lisa Gardiner/UCAR
2. Have students read the EPA Sun Safety Action Steps and list the steps that are recommended for staying away from UV light from the Sun.
3. Ask students whether they think some actions described in the reading are more effective than others. Have each group of 3-4 students brainstorm ten questions that they have about the effectiveness of different actions described in the reading. (For example, students may wonder how effective it is to stay in the shade of a tree. They may wonder what types of clothing are best for covering up or whether the amount of sunscreen makes a difference.)
4. Tell students that they are going to design an investigation to test one of these questions. They will use the blacklight to model ultraviolet light from the Sun and test how much the tonic water fluoresces when different actions are taken to block the UV light.
5. Demonstrate how actions to block the ultraviolet light can be explored using the tonic water. For example, ask students if they think UV light can be transmitted through the windows of the classroom like the visible light is transmitted. Place a piece of glass between the blacklight and one of the cups of tonic water. The florescence should stop for the blocked cup (glass typically doesn’t transmit UV) but not for the other cup. Tell students that the items described in the reading (clothing, sunscreen, tree branches) can be put between the light and tonic water like “screens” to assess whether the UV light is transmitted through them. Point out that the amount of florescence is relative, so students will need to compare with the unblocked cup.
6. Have students work in their groups to decide which of their ten questions they would like to test and plan the investigation. To communicate their plan, have students write:
- the question they will explore
- the supplies they will need for their “screens”
- the method they will use to test their question
7. Review each group’s project plan noting if the method will address the question and whether supplies are practical. (Students might need advice about supplies and methods.)
8. Have student groups make the “screens” that they will place between the light and tonic water. (Note: See About Making “Screens” in the Background section for information and ideas.)
9. Have students test their screens between the light and the tonic, recording the difference in florescence with photos or by documenting the blue florescence in their notebooks with colored pencils. Have students try their screens multiple times to see if results are consistent. (This data is qualitative, thus students will need to describe the amount of blue florescence from the tonic water relative to other amounts.)
10. Have students create a graphic to describe their data and make a poster (or a presentation slide) with their group’s question, their graphic results, and their conclusion.
11. Lead a gallery walk of the posters in which students review the results of all groups. (If students have made slides instead of posters, have each group present in front of the class.)
12. Have students discuss what they learned about the best ways to stay safe from UV light. If time allows, have students consider whether they have more questions about staying safe from UV light after the experiment.