Lesson - Expose: UV Ray

GOAL
To use reading and research skills to understand that sunlight travels in a straight line until it strikes an object and is deflected, scattered, or absorbed

BACKGROUND
Ultraviolet radiation (UV), which is found in sunlight, is an invisible form of energy that travels through air and objects. There are three types of UV rays: UVA, UVB, and UVC. UVA, while less powerful than UVB, penetrates deeply into the skin and contributes to skin aging and wrinkling. UVB rays are the most powerful and the most dangerous, causing sunburns and skin cancer. Lethal UVC rays are completely absorbed by the ozone layer and do not reach earth.

Most sunscreens contain molecules that absorb UV rays. However, some sunscreens contain zinc oxide or titanium dioxide that deflects, scatters, and absorbs UV radiation away from the skin. Some clothing can also deflect, scatter, and absorb UV rays to protect the body.

PREP
Darken the room, and shine a flashlight. Can students see a beam? Clap two chalkboard erasers in front of the flashlight. Explain that the chalk dust helps us see rays of light, or light waves. (The waves deflect, or bounce off, the chalk particles into our eyes.) Print out the Expose: UV Ray Student Reproducible, photocopy, and distribute to your students. (Click here for the pdf reproducible*)

ACTIVITY

1. As a class, read the interview aloud. Write down and define difficult words or concepts.
2. Ask students to write their own questions for UV Ray on the lines provided.
3. Have students trade pages with a partner. Challenge them to find the answer to their partner's question, using print or online resources. Alternatively, you may assign this task as homework. Ask students to list the resources that they used.
4. Have students read the question and their answers aloud.

WRAP-UP
Ask your students: Can you see UV rays? (No.) Do UV rays shine only in the summer? (No, they are present year-round.) What can help stop a UV ray? (A solid barrier such as clothing, or sunscreen.) What makes these things less effective? (If clothing is wet or has holes; if sunscreen isn't reapplied; if sunscreen is rubbed or washed off.)

EXTENSION: See UV
Fill one clear plastic cup with tonic water. Put the cup in direct, overhead sunlight and hold black paper behind it. Have students describe what they see. (The tonic water should have a blue glow at the surface.) Explain that a special ingredient in tonic water (quinine) glows in UV light. Spread a thin coating of sunscreen on a clear overhead transparency sheet. Place the coated sheet between the sun and the cup. What happens? (The sheet should absorb some UV rays and decrease the glow effect.) Have students predict: Would a lower sun position affect your results? Have students repeat the experiment to find out. (Less UV should decrease the glow). Try the experiment again with plain water to show how UV rays are invisible.