Author: Beth Kennedy
Source: IPEC Polymer Ambassadors
Students explore Ultraviolet (UV) detecting beads, conduct several investigations with them to find sources of UV radiation, and find materials that block U V radiation. Eventually students will realize that over-exposure to UV radiation is harmful to their eyes and skin.
What should students know as a result of this lesson?
What should the students be able to do as a result of this lesson?
If the students have no prior knowledge of UV beads, make a UV detecting bracelet by stringing as many beads as desired on a piece of thick string, ribbon, yarn or a pipe cleaner. If using a pipe cleaner, tuck/wrap ends carefully around the band to prevent being poked. Place bracelet on wrist and go to a clear window, or go out into the sunlight. Watch the beads change color. Get out of the sunlight and watch the beads change back to white. Allow students to test this as many times as needed to get their minds thinking.
Discuss that the beads change color in the presence of sunlight, but turn white when shielded from it. Students will want to test their beads against other light sources. Have other sources such as flashlights, overhead projector light, regular fluorescent light etc. available for them to test.
Introduce a fluorescent black light to the students. Discuss how this special light works. (http://science.howstuffworks.com/black-light1.htm) Demonstrate it on their clothing, shoes, teeth, and then their bracelets. Students will see that the fluorescent black light affects their bracelets. The students should come to the conclusion that their beads detect UV light.
Inform students how the beads work, or have them find out on their own at: www.teachersource.com (Educational Innovations, Inc.)
Once students conclude that the beads detect harmful, UV radiation, have them create an experiment in chart/graph form that shows objects to test for possible shielding of UV radiation using the tinted or clear cellophane, sunglasses, lotion sunscreens of various strengths, tinted plastic containers or glass jars from the materials section. Any other source that students believe may be used as a shield or sunscreen may be added here as well. (scarves, T-shirts, umbrellas, etc.) Have students state any conclusions found from testing these materials at the bottom of the graph/chart page.
Lead the groups in a discussion of how they are aware of harmful UV radiation and how it can affect humans, animals, plants and manmade things. (sunlight fades/bleaches cloth and wood etc.) Then discuss that after people found that UV radiation harmed things they worked to create shields of UV rays in the forms of tints, colors, etc. (tinted glass bottles to store foods, medicines, etc.)
Students can be introduced to another UV detecting source - UV detecting nail polish. Have them see how this works.
The teacher should make certain that the students have prior knowledge about sunlight as a primary source of energy. The teacher will also want to break sunlight or another light into the visible spectrum with a prism or a diffraction grating placed on an overhead projector. This will lead into the discussion of light that is not part of the visible spectrum, such as infrared and UV light. The teacher and the students can then discuss that UV light is the invisible radiation that can give you a sunburn and injure your eyes/vision if you're not careful.
The teacher may also wish to do a lesson on the study of human skin before using the UV beads. Students will understand the need for protecting this vital body "organ" once they learn more about how important it is. An excellent lesson for this is found in Science and Children , Nov./Dec.1999, Volume 37, Number 3. Students learn about skin using the learning cycle structure in this article. It addresses NSES Grades 5-8 Content Standard C and Content Standard A Science as Inquiry.
Common Core Standards:
Teacher background knowledge: Visible spectrum.
If a prism is used to break-up the radiated light from an object into its component colors, the "visible light" which our eyes can see makes up only a small part of the total spectrum. Visible light runs from blue to green to yellow to orange to red. Red light is the least energetic of the colors of visible light and blue is the most energetic. Beyond the red end of the visible part of the spectrum lies the infrared and radio radiation. Infrared "light" is familiar to us as heat, while radio waves are used for TV and radio broadcasts
Beyond the blue end of the visible spectrum lie ultraviolet light, X-rays and gamma rays. All of the X-rays, gamma rays, and ultraviolet light emitted by stars are absorbed by the Earth's atmosphere. Many scientists are interested in studying the invisible universe of ultraviolet light, since the hottest and most active objects in the universe give off large amounts of ultraviolet energy.
Teacher Background knowledge: How the Fluorescent Black Light Works
The conventional black light design is simply a fluorescent lamp with a couple of important modifications. Fluorescent lamps generate light by passing electricity through a tube filled with inert gas and a small amount of mercury. When energized, mercury atoms emit energy in the form of light photons. They emit some visible light photons, but mostly they emit photons in the ultraviolet (UV) wavelength range. Since UV light waves are too short for us to see -- they are completely invisible -- fluorescent lamps have to convert this energy into visible light. They do this with a phosphor coating around the outside of the tube.
Phosphors are substances that give off light (or fluoresce) when they are exposed to light. In a fluorescent lamp, the emitted light is in the visible spectrum. The phosphor gives off white light we can see.
Black lights work on this same principle. A tube black light is a basically a fluorescent lamp with a different sort of phosphor coating. This coating absorbs harmful short-wave UV-B and UV-C light and emits UV-A light (in the same basic way the phosphor in a fluorescent lamp absorbs UV light and emits visible light). The "black" glass tube itself blocks most visible light, so in the end only benign long-wave UV-A light and some blue and violet visible light pass through.
Teacher Background knowledge about fluorescent black lights can be found at: http://science.howstuffworks.com/black-light1.htm
Students will want to choose sunglasses with UV protection, and make certain that the sun blocks they put on their skin are the most effective for their skin types. If students are particularly sensitive to sunlight, protective clothing might be necessary.
Look at students' experimentation charts and conclusion statements for demonstration of proper experimentation and understanding. Assess how persuasive the paragraphs were in deciding which is more effective, UV beads or nail polish.
Grouping Suggestions: Partners or possibly groups of three.
Pacing/Suggested Time: 45-60 minutes, and another class time for sharing photographs.