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Detecting Things We Cannot See:
Learning the Concepts of Control
and Variable in an Experiment

From the Spring-Summer 1997 sciencelines

Submitted by Anita Brook-Dupree, 1996 TRAC teacher at Fermilab, Teacher, Alternative Middle Years School, Philadelphia, PA.

Particle physicists at Fermilab in Batavia, Illinois are faced with the problem of detecting the presence of sub-atomic particles they cannot see. During my summer as a TRAC teacher at Fermilab, I tried to think of ways to teach middle school students about things we cannot see. I want to thank my nine-year-old daughter Gia for the idea for the following activity. I was lamenting that I could not come up with ideas of how to relate the work of Fermilab scientists to anything that my students would understand. Then I was reminded by my daughter, that when I brought her to school on the annual "Take Your Daughter to Work Day" in April, she saw me doing Sunprints with my students. Sunprint paper detects the presence of ultraviolet light, which is something we cannot see.

Grade level: K-8th grade


1. Students will make a simple Sunprint and learn the term CONTROL as used in an experiment.

2. Students will generate a list of VARIABLES, learn the term variable, and test one of the variables.

Materials: ·

Sunprint paper can be purchased inexpensively at various science museum gift shops or directly from the manufacturer:

The Lawrence Hall of ScienceUniversity of California at BerkeleyBerkeley, CA 94720(510) 642-1016 FAX (510) 642-1055


This activity will take two class periods. First do a basic Sunprint with the students. This will serve as the CONTROL. Put the term CONTROL on the board and discuss the term CONTROL before you start. Tell the students that this is the print to which other prints will be compared.

The directions for a basic Sunprint are on the package of Sunprint paper that you will need to purchase to do this activity.

1. Select an item such as a key, leaf, or a paper cut out of a heart, a snowflake, or the student's initials.

2. Assemble the parts of the Sunprint kit in this order: a piece of cardboard, Sunprint paper blue side up, item, acrylic sheet.

3. Expose this assembly to the sun until the paper turns almost white. This may take from 1-5 minutes, depending on the sunlight. Try not to over expose the Sunprint paper.

4. Quickly rinse the Sunprint paper in a tub of water for about one minute. Dry the print flat.

Students may want to frame their Sunprints with construction paper. Save all the Sunprints so they can be compared to the prints done during the next class period.

During the next class period have students think in terms of VARIABLES. Put the word VARIABLE on the board and explain that this is the thing that will change. Have students brainstorm ideas to turn this art activity into an experiment. I have students write ideas about what they could change. These variables can be tested and the changes may beobservable on the paper. I encourage students to think like scientists. A list of variables might look like this:

The list can, and will go on and on with the teacher's help. Students love to write on the board, so I usually have a recorder write the ideas as they come in from the groups of four. After the list has been generated, students may choose a variable. Every one gets Sunprint paper in a black envelope and an opportunity to do the experiment. My favorite variable is the use of sunscreens on the acrylic plate using different SPF. The results are quite dramatic.

Background Information:

Sunprint paper is sensitive to UV light. When I called the Lawrence Hall of Science they told me that they cannot disclose the nature of the chemical that makes the paper UV sensitive. It is a trade secret. I was told that the proceeds from the sale of this paper are used to continue many of the educational programs funded by the Lawrence Hall of Science. They will FAX you an information sheet about their product.

Ultraviolet light, invisible to our eyes, is a higher energy type of light than the visible light that we ordinarily see. Sunprint paper absorbs ultraviolet light. Ultraviolet light causes a chemical change in the paper, which changes the color from blue to white. Then energy from ultraviolet light is what causes the chemical make-up of the paper to change. Water reacts with the unexposed Sunprint paper (paper covered by an object) changing the color to white.

Opaque objects that do not allow any UV light to pass will result in white areas on the Sunprint paper. Objects that allow UV light to pass will result in dark blue areas. Translucent objects, like a leaf or a crystal, will allow some UV light to pass, causing the paper to partially react and turn blue.

Follow-up activities:

Follow-up activities, depending on the age group you are working with, could include researching the electromagnetic spectrum to find the difference between ultraviolet light and other types of light. Another related educational topic is the depletion of the ozone layer, which allows more ultraviolet light to reach the earth.