Computer

22

UV Light and Clothing

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Figure 1 shows the location of UV light in the electromagnetic spectrum. Notice that the ultraviolet band is broken into three types referred to as UVA, UVB, and UVC. The most harmful of these three, UVC light, is absorbed by the atmosphere and does not reach the Earth’s surface. UVA light is deeppenetrating and causes tanning, wrinkles, and some forms of skin cancer. UVB light is also responsible for many skin problems such as sunburns and several forms of skin cancer.

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New fabrics are being introduced to the clothing market that claim to block all UV light. There are additives to put in your wash to make your clothes more efficient at blocking UV light. But are these added expenses needed? How well do your current clothes and swimming suits protect your skin?

Figure 1

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OBJECTIVES

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In this experiment, you will measure the levels of UVB light that can pass through fabrics. You will compare fabric colors and types. You will then get the fabrics wet and again measure the amount of UVB light passing through.

In this experiment, you will • • •

Use a UVB Sensor to measure UVB light. Determine the amount of UVB light allowed through various fabrics. Determine whether the UVB-blocking abilities of fabrics change when wet.

MATERIALS

ring stand and clamp 6 squares of fabric two 4 × 6 inch index cards scissors cup of water stopwatch

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computer Vernier computer interface Logger Pro UVB Sensor coin (approximately 2 cm in diameter) tape

PRE-LAB PROCEDURE 1. Obtain the six pieces of fabric assigned by your teacher. There will be two types of fabric, three colors of each, for a total of six. Make sure that the people who handle the fabrics do not have any sunscreen or lotion on their hands. 2. In the spaces provided on the data table, fill in the information on fabric colors and types. Samples 1–3 should be one type of fabric and 4–6, the other.

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Computer 22 3. Prepare your test cards. a. Obtain two 4 × 6 inch index cards. b. Using the coin as your guide, draw three circles on each test card in the locations shown in Figure 2. The dashed lines indicate where the squares of fabric will be taped. c. Number the circles 1–6. d. Use scissors to cut out the circles. e. Tape the six squares of fabric over their assigned circle as shown in Figure 2. Make sure the tape is only on the edges and not covering any part of the circle.

2 3

1

Figure 2

Choosing a Method for Data Collection Method 1 uses remote data collection. It should be used if you have a LabPro interface with a desktop computer. Method 2 requires that the computer remains attached to the interface. This method should be used if you have a Vernier computer interface with a laptop computer that can be taken outside.

METHOD 1: Using LabPro Remotely 1. Have your test cards ready. 2. Connect the UVB Sensor to LabPro. 3. Prepare the computer for data collection by opening the file “22 Light and Clothing” in the Earth Science with Vernier folder. 4. Familiarize yourself with the sampling procedure by studying Table 1. Notice that data collection will last for 120 seconds. You will first monitor 15 seconds of full sunlight, then 15 seconds for each fabric sample, finally 15 more seconds of full sun.

Table 1: Sampling procedures Time (seconds)

Sample being measured

0 – 15

full sun

5. Once you are familiar with the sampling procedures, choose Remote ` Remote Setup from the Experiment menu. A summary of your setup will be displayed.

15 – 30

1

30 – 45

2

45 – 60

3

6. Click . The interface can now be disconnected from the computer. Important: (1) Be very careful not to press the START/STOP button on the interface until you are ready to begin collecting data, and (2) do not close the Logger Pro computer program.

60 – 75

4

75 – 90

5

90 – 105

6

105 – 120

full sun

7. Take your equipment outside. 8. Use the shadow of the UVB Sensor to aim it correctly without looking directly at the sun. a. Hold the sensor with your thumb and first finger, pointing the sensor in the general direction of the sun. 22 - 2

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UV Light and Clothing b. Find the sensor’s shadow and observe how it changes shape as you move the sensor around. c. Move the sensor around until the shadow becomes a small round circle. This indicates that the sensor is now pointing directly at the sun. d. Keeping this sensor orientation in mind, clamp the UVB Sensor onto the ring stand as shown in Figure 3. e. Once the sensor is securely on the ring stand, use the shadow again to make final adjustments to assure that the sensor is pointing directly at the sun. 9. Practice holding one of your sample circles over the tip of the UVB Sensor. It is okay if the fabric lightly touches the tip of the sensor. 10. When everything is ready, have the timer start the stopwatch while another person simultaneously presses the START/STOP button on the LabPro. Data collection will begin. 11. Take your readings using Table 1 as your guide. Data collection will stop automatically after 120 seconds. 12. When data collection is finished, go back to the computer and reattach the interface. If a Remote Data Available window appears, simply click the YES button and choose to retrieve remote data into the current file. If a window does not appear when the interface is reconnected, choose Remote ` Retrieve Remote Data from the Experiment menu. 13. Determine the average UVB intensity for each sample.

Figure 3

a. Study your graph and identify the eight 15 second sections. b. Using your mouse, click and drag a box to select the flattest region of the first 15 second section. c. Click the Statistics button, . The mean, or average, value for the selected data is listed in the Statistics box on the graph. Record this value in the “Dry Fabric” column of the data table. d. Close the Statistics box. 14. Repeat Step 13 for the six fabrics. 15. Wet the fabric samples by gently pouring a small amount of water on each. Some fabrics may repel the water and will need repeated applications before becoming saturated. The card will get wet, too. This is fine. 16. Once all six samples are saturated with water, gently shake the cards to remove any extra drops of water that could drip on the UVB Sensor. It is all right if the damp fabric touches the end of the sensor, but make sure no water gets in the sensor. 17. Repeat Steps 5–14 with the wet fabric, recording the UVB values in the “Wet fabric” column of the data table.

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Computer 22

METHOD 2: Interface Remains Attached to Computer 1. Have your test cards ready. 2. Connect the UVB Sensor to the Vernier computer interface. 3. Prepare the computer for data collection by opening the file “22 Light and Clothing” in the Earth Science with Vernier folder. 4. Familiarize yourself with the sampling procedure by studying Table 1. Notice that data collection will last for 120 seconds. You will first monitor 15 seconds of full sunlight, then 15 seconds for each fabric sample, finally 15 more seconds of full sun. 5. Take your equipment outside.

Table 2: Sampling procedures Time (seconds)

Sample being measured

0 – 15

full sun

15 – 30

1

30 – 45

2

45 – 60

3

60 – 75

4

75 – 90

5

90 – 105

6

105 – 120

full sun

6. Use the shadow of the UVB Sensor to aim it correctly without looking directly at the sun. a. Hold the sensor with your thumb and first finger, pointing the sensor in the general direction of the sun. b. Find the sensor’s shadow and observe how it changes shape as you move the sensor around. c. Move the sensor around until the shadow becomes a small round circle. This indicates that the sensor is now pointing directly at the sun. d. Keeping this sensor orientation in mind, clamp the UVB Sensor onto the ring stand as shown in Figure 4. e. Once the sensor is securely on the ring stand, use the shadow again to make final adjustments to assure that the sensor is pointing directly at the sun. 7. Practice holding one of your sample circles over the tip of the UVB Sensor. It is okay if the fabric lightly touches the tip of the sensor. 8. When everything is ready, have the timer start the stopwatch while another person simultaneously clicks the button. Data collection will begin. 9. Take your readings using Table 2 as your guide. Data collection will stop automatically after 120 seconds. 10. Determine the average UVB intensity for each sample. a. Study your graph and identify the eight 15 second Figure 4 sections. b. Using your mouse, click and drag a box to select the flattest region of the first 15 second section. c. Click the Statistics button, . The mean, or average, value for the selected data is listed in the Statistics box on the graph. Record this value in the “Dry Fabric” column of the data table. Close the Statistics box. 22 - 4

Earth Science with Vernier

UV Light and Clothing 11. Repeat Step 10 for the six fabrics. 12. Wet the fabric samples by gently pouring a small amount of water on each. Some fabrics may repel the water and will need repeated applications before becoming saturated. The card will get wet, too. This is fine. 13. Once all six samples are saturated with water, gently shake the cards to remove any extra drops of water that could drip on the UVB Sensor. It is all right if the damp fabric touches the end of the sensor, but make sure no water gets in the sensor. 14. Repeat Steps 8–11 with the wet fabric, recording the UVB values in the “Wet fabric” column of the data table.

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DATA Sample

Full Sun

Dry fabric UVB 2 (mW/m )

Dry fabric UVB (%)

Wet fabric UVB 2 (mW/m )

100

Wet fabric UVB (%)

Color

Fabric type

100

N/A

N/A

1

2

3

4

5

6

PROCESSING THE DATA 1. Calculate the percent UVB light allowed through by each fabric sample and record in the appropriate space in the data table. % UVB light =

UVB with fabric UVB of full sun

× 100

2. Did the type of fabric make any difference in the amount of UVB light allowed through? Use your data to explain your answer.

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UV Light and Clothing 3. Did the color of the fabric make any difference in the amount of UVB light allowed through? Use your data to explain your answer.

4. Did any of the fabrics let through more or less UVB light when wet? Use your data to explain your answer.

5. Special UV-blocking clothing is now being sold. Based on your results, do think it is worth the extra money for this specialty fabric? Explain.

EXTENSIONS 1. Obtain and test fabric that claims to block all UV light. 2. Obtain and test fabric that claims to allow a person to tan right through it. 3. Test a wider variety of fabrics to confirm or deny your conclusions above. 4. UVA light is not only responsible for tanning your skin, but for wrinkles, cataracts and some types of skin cancer as well. If your school has a Vernier UVA Sensor, test the same fabrics for their degree of UVA protection.

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Vernier Lab Safety Instructions Disclaimer THIS IS AN EVALUATION COPY OF THE VERNIER STUDENT LAB.

This copy does not include: z

Safety information

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Essential instructor background information

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Directions for preparing solutions

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Important tips for successfully doing these labs

The complete Earth Science with Vernier lab manual includes 33 labs, 6 projects, and essential teacher information. The full lab book is available for purchase at: http://www.vernier.com/cmat/esv.html

Vernier Software & Technology 13979 S.W. Millikan Way • Beaverton, OR 97005-2886 Toll Free (888) 837-6437 • (503) 277-2299 • FAX (503) 277-2440 [email protected] • www.vernier.com