Are All Sunglasses Created Equal?

Computer 20 Are All Sunglasses Created Equal? n co Figure 1 shows the location of UV light in the electromagnetic spectrum. Notice that the ultra...
Author: Barnaby Scott
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Computer

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Are All Sunglasses Created Equal?

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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 deep-penetrating 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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Have you ever been sunburned? If so, you are familiar with the fact that ultraviolet (UV) light can damage your skin. But UV light can damage your eyes as well. UV light is absorbed by your eye and can cause a burn just like a sunburn on your skin. This condition, sometimes called snowblindness or welders flash, usually only lasts a few days. But UV light can also cause cataracts – cloudy spots on the lens of your eye that could require surgery or lead to blindness. So how do you protect your eyes? Do sunglasses do a good job of blocking UV radiation? Are expensive sunglasses better than cheap sunglasses? Are sunglasses better than regular eye glasses? These are some of the questions you will investigate in this experiment.

Figure 1

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In this experiment, you will measure the UVB-blocking performance of various types of sunglasses and eyeglasses.

OBJECTIVES

In this experiment, you will

Use a UVB Sensor to measure UVB light. Determine the percent UVB light that is blocked by various kinds of sunglasses and regular eyeglasses.

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MATERIALS

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computer Vernier computer interface Logger Pro

UVB Sensor selection of sunglasses and glasses stopwatch or digital watch

PRE-LAB PROCEDURE 1. Obtain two pairs of sunglasses and one pair of regular eyeglasses for testing. Try to use sunglasses from two different price ranges. 2. In the spaces provided on the data table, fill in the UV protection claims on label, lens material, lens color, and price. If the owner of the glasses does not know these facts, find them by going back to the store where they were purchased or check the manufacturer’s web site.

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Choosing a Method 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 three pairs of glasses ready. 2. Connect the UVB Sensor to the LabPro. 3. Prepare the computer for data collection by opening the file “20 Sunglasses” in the Earth Science with Vernier folder. 4. Familiarize yourself with the sampling procedure. a. Look at the graph on the screen and notice that data collection will last for 120 seconds. b. Over this 120 second run, you will alternate between 20 seconds of monitoring the sun directly and 20 seconds of monitoring the sun through each of your three pairs of glasses. One person will be the timer who will call out the 20 second intervals. c. Study Table 1 so that you will be familiar with the sampling procedures before going outside. Table 1: Sampling procedures Time (seconds)

Sample being measured

0 – 20

Sun

20 – 40

Pair 1

40 – 60

Sun

60 – 80

Pair 2

80 – 100

Sun

100 – 120

Pair 3

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. 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.

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Earth Science with Vernier

Are All Sunglasses Created Equal? 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. 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 2. 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. When everything is ready, have the timer start the stopwatch while another person simultaneously presses the START/STOP button on the interface. Data collection will begin.

Figure 2

10. Take your readings using Table 1 as your guide. When you monitor through a pair of glasses, place the lens directly over the tip of the UVB Sensor as shown in Figure 1. Try not to bump the sensor. Data collection will stop after 120 seconds. 11. 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. a. Study your graph and identify the six 20 second sections. b. Using your mouse, click and drag a box to select the flattest region of the graph while you were testing Pair 1. 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 data table. d. Close the Statistics box. 12. Repeat Step 11 for the other pairs of glasses. 13. Print copies of your graph as directed by your teacher.

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METHOD 2: Interface Remains Attached to Computer 1. Have your three pairs of glasses ready. 2. Connect the UVB Sensor to the Vernier computer interface. 3. Prepare the computer for data collection by opening the file “20 Sunglasses” in the Earth Science with Vernier folder. 4. Familiarize yourself with the sampling procedure. a. Look at the graph on the screen and notice that data collection will last for 120 seconds. b. Over this 120 second run, you will alternate between 20 seconds of monitoring the sun directly and 20 seconds of monitoring the sun through each of your three pairs of glasses. One person will be the timer who will call out the 20 second intervals. c. Study Table 2 so that you will know the sampling procedures before you begin. Table 2: Sampling procedures Time (seconds)

Sample being measured

0 – 20

Sun

20 – 40

Pair 1

40 – 60

Sun

60 – 80

Pair 2

80 – 100

Sun

100 – 120

Pair 3

5. Take your equipment outside. 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 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. 7. When everything is ready, have the timer start the stopwatch while another person simultaneously clicks the button. Data collection will begin.

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Figure 3

Earth Science with Vernier

Are All Sunglasses Created Equal? 8. Take your readings using Table 2 as your guide. When you monitor through a pair of glasses, place the lens directly over the tip of the UVB Sensor as shown in Figure 3. Try not to bump the sensor. Data collection will stop after 120 seconds. 9. Determine the average UVB intensity for each pair of glasses. a. Study your graph and identify the six 20 second sections. b. Using your mouse, click and drag a box to select the flattest region of the graph while you were testing Pair 1. 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 data table. d. Close the Statistics box. 10. Repeat Step 9 for the other two pairs of glasses. 11. Print copies of your graph as directed by your teacher.

DATA Pair 1

Pair 2

Pair 3

UV protection claims on label

Lens material (glass/plastic)

Lens color

Approximate price

2

UVB Intensity of the sun (mW/m ) UVB Intensity while covered with 2 glasses (mW/m )

UVB blockage (%)

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PROCESSING THE DATA 1. Calculate the percent UVB blockage of each pair of glasses and record in the data table. % UVB blockage = UVB of sun – UVB with glasses × 100 UVB of sun 2. According to your data, did the following factors affect the UVB blocking abilities of the glasses you tested? Answer yes or no and explain your reasoning. a. UV protection claims on the label?

b. Lens material?

c. Lens color?

d. Price?

EXTENSIONS 1. Test a wider variety of sunglasses and glasses to confirm or deny your conclusions above. 2. UVA light is not only responsible for tanning your skin, but for wrinkles, cataracts and some types of cancer as well. If your school has a Vernier UVA Sensor, test the same glasses 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

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