Special Frisbees Detect Ultraviolet Radiation

This experiment will help students understand that ultraviolet radiation is present in natural outdoor light and that the intensity of the light varies with season and time of day.

Background

The energy from the sun includes not only visible light but also wavelengths longer (infrared) and shorter (ultraviolet) than visible light. The wavelengths of visible light increase from the blue to the red end of the spectrum. Shorter than blue are wavelengths referred to as ultraviolet (UV). Ultra means beyond, so ultraviolet means beyond (actually, shorter than) violet.

The amount of UV radiation reaching the earth's surface depends on the distance it travels through the atmosphere. During morning hours, UV radiation must travel through more of the earth's atmosphere because the sun is lower on the horizon. At noon the rays travel a shorter distance through the atmosphere because the sun is more directly overhead.

If you would like to extend this activity into an inquiry-based laboratory for your students, a guide has been included along with a sample lab report format.

Learning Goals

1. Students will understand that ultraviolet radiation is present in natural outdoor light.
   
   
2. Students will be able to demonstrate that UV radiation can be blocked or filtered by various substances.
   
   
3. Students will be able to explain that the amount of UV radiation varies with time of day.
   

Alignment to National Standards

National Science Education Standards

• Physical Science, Transfer of Energy, Grades 5 to 8, pg. 155, Item #6: "The sun is a major source of energy for changes on the earth's surface. The sun loses energy by emitting light. A tiny fraction of that light reaches the earth, transferring energy from the sun to the earth. The sun's energy arrives as light with a range of wavelengths, consisting of visible light, infrared, and ultraviolet radiation."
  
  
• Physical Science, Interactions of Energy and Matter, Grades 9 to 12, pg. 180, Item #1: "Waves, including sound and seismic waves, waves on water, and light waves, have energy and can transfer energy when they interact with matter."
  
  
• Physical Science, Interactions of Matter and Energy, Grades 9 to 12, pg. 180, Item #2: "Electromagnetic waves result when a charged object is accelerated or decelerated. Electromagnetic waves include radio waves (the longest wavelength), microwaves, infrared radiation (radiant heat), visible light, ultraviolet radiation, x-rays, and gamma rays. The energy of electromagnetic waves is carried in packets whose magnitude is inversely proportional to the wavelength."

Benchmarks for Science Literacy, Project 2061, AAAS

• The Physical Setting, Motion, Grades 6 to 8, pg. 90, Item #1. "Light from the sun is made up of a mixture of many different colors of light, even though to the eye the light looks almost white. Other things that give off or reflect light have a different mix of colors."
  
  
• The Physical Setting, Motion, Grades 6 to 8, pg. 90, Item #5. "Human eyes respond to only a narrow range of wavelengths of electromagnetic radiation—visible light. Differences of wavelength within that range are perceived as differences in color."
  
  

Grade Level/Time

• Grade level: 5 to 9
  
  
• Time:
  
  Time for this activity is highly variable and dependent on the level of sunlight and type of test selected. This activity would serve well as a scientific inquiry project for even younger students. Allow students to work in teams, have them select an experiment to run on the Frisbees (plastic shields, sunscreen, etc.), decide how to do it, and carry it out. This will take at least two periods. Simpler demonstration activities will take correspondingly less time.
  

Materials

• 5 UV-sensitive Frisbees (small), or one large one cut up into pieces
  
  
• Squares of plastic of various thickness (1/32 to 1/2" thick). Plastic scraps may be obtained at hardware stores or glass companies.
  
  
• Tray
  
  
• Cover
  
  
• Black light may be used on cloudy days
  

Note: Frisbees are manufactured by Wham-O Manufacturing Co. (www.wham-o.com) and can be found in many local toy stores.

Procedure

Note: At the end of this activity write-up, there are suggestions for teachers wishing to use a more inquiry-based approach. A sample student lab write-up is also included.

1. Place Frisbees on tray.
   
   
2. Leave one Frisbee uncovered. Cover each of the others with plastic sheets of various thickness.
   
   
3. Make a data sheet similar to the one suggested at the end of this activity.
   
   
4. Cover the entire tray with a cloth to block all light. Carry the tray outside and place in direct sunlight.
   
   
5. Remove cover in sunlight and fill out data sheet.
   

Observations and Questions

1. Did the Frisbees change color when exposed to normal room lighting? (Not usually.) Why or why not? (Because there is very little UV radiation in indoor lightning.)
   
   
2. What happened to the color of the Frisbees in sunlight? (They turned pink.) Why do you think these results occurred? (The UV light causes a photochemical reaction that causes the Frisbee to turn pink.)
   
   
3. What effect did the various pieces of plastic have upon the color of the Frisbees? (The Frisbees did not turn color.) Why do you think these results occurred? (Probably the plastic blocked the UV light so the photochemical reaction was unable to occur.)
   
   
4. Relate this activity to the interaction of ozone and UV radiation in the stratosphere. (The thinner the layer of ozone, the more UV radiation that will get through. For example, a typical amount of ozone is 300 Dobson units. If all the ozone in a column were to be compressed to standard temperature and pressure (STP) (0 deg C and 1 atmosphere pressure) and spread out evenly over the area, it would form a slab approximately 3 mm thick. One Dobson Unit (DU) is defined to be 0.01 mm thickness at STP. The unit is named after G.M.B. Dobson, one of the first scientists to investigate atmospheric ozone (~1920 - 1960). He designed the 'Dobson Spectrometer' - the standard instrument used to measure ozone from the ground. The Dobson spectrometer measures the intensity of solar UV radiation at four wavelengths, two of which are absorbed by ozone and two of which are not. In the ozone "hole," the thickness has dropped to as low as 100 DU.)

Extensions

1. Test the effectiveness of different types of filters, such as different types of plastics (acrylic, Lucite, Plexiglas), glass (you can use glass slides; stack a number together for different thicknesses), water, different types of cloth, sunscreens with different SPF numbers and/or different brands, different types of artificial lights (fluorescent, incandescent, heat lamp, black lights, etc.).
   
   
2. Test the Frisbees at different times during the day, under different degrees of cloud cover, and at different seasons. Can you relate the amount of UV radiation to different amounts of atmosphere that solar radiation travels through?
   

Sample Data Chart

Assessment Ideas

• As noted above, this would serve well as a scientific inquiry task and would allow the teacher to assess the students' understanding of UV effects as well as their ability to design and conduct a simple, independent experiment.
  

Modifications for Alternative Learners

• No modifications should be necessary.

Notes to Teacher

Suggestions to implement this activity through an inquiry approach

1. Collect an assortment of substances such as: sunscreens and tanning lotions, lip balm and/or face creams, UV protective additive for paint (hardware stores should carry these), sheets of various plastic films (food wrap, mylar, acetate), and small pieces of clear acrylic and polycarbonate.
   
   
2. To avoid reliance on clear, sunny days as your UV source, you may use commercial UV lamps of various types (many are sold as 'mineral-lights' and are used to identify fluorescent minerals), but whenever using UV lamps, use great caution in limiting student exposure to the lamps.
   
   
3. Use any acceptable form of a lab write-up or oral lab report. Students should have the opportunity to explain what the question is and why it's important, describe in detail their experimental procedure, report their results in text and graphic form (graphs, tables), and explain how the data they collected answers the question. An example lab write-up format (intended for upper-level students) is appended.
   

Example Lab Report Format

In this class we will frequently be doing labs that you design and carry out on your own. For these labs, you will turn in a report, either on paper or on disk (your choice) that follows the following format:

1. TITLE: The title should specifically describe what the lab is about ("The effect of insecticides on plant growth," not "Chemicals and plants").
   
   
2. INTRODUCTION: Tell the reader why you are doing the study. Give enough background information so the reader will understand why the subject and the study is important. Tell the reader what you are trying to figure out in the form of a clear, logical, and answerable question.
   
   
3. MATERIALS: List all the supplies that you used so someone else could use exactly the same materials when repeating your study.
   
   
4. PROCEDURE: Pretend your lab is like a recipe and that you are writing for a reader not as smart as you. You have to describe exactly what to do and how to do it or the reader will probably mess it up. Procedures are best written in a numbered list (step 1, step 2, etc.) rather than in paragraph form, but if you like the paragraph form and can write very clearly, you may use it. If you've done it correctly, a younger student ought to be able to follow your instructions. Drawings or diagrams are often helpful. Be sure to identify CONTROL treatments and REPLICATES clearly in your procedure.
   
   
5. RESULTS: Data can take many forms, but it all needs to be clearly shown to the reader. You may use drawings, tables, or graphs, depending on what you are trying to show, but all have to be very well labeled, with titles and all units shown. You must also write in paragraph form what you found. This is where you draw the reader's attention to the most important or useful parts of your data. We will discuss these issues further in class.
   
   
6. DISCUSSION AND CONCLUSION: This is the heart of the lab! Plan to spend LOTS of time on this section! This section should be written in paragraph form, not in a list. There are several parts to a good discussion section:
   
   a. Summarize why you did the lab and how you did it.
   
   b. Summarize what you found.
   
   c. Relate your findings specifically back to your purpose or question. Did you fulfill the purpose, answer the question? (It's totally OK if the answer is no; many experiments don't turn out to be what we expect them to be.) Either way, explain why.
   
   d. Discuss sources of error: These are things that you couldn't control—faulty equipment, limits on time or resources, other things you didn't plan on. Don't cop-out by just reporting that you messed up.
   
   e. If I wanted to pursue this research, what would you recommend that I do next? Leave me with a sense of where the research would go from here.