Name Date Class Lab 25: Color in Light Color in Light Purpose To observe light color addition and subtraction through filters, receptors in the eye, different types of color blindness, and prisms Background Throughout the ages, philosophers and scientists speculated about the substances that made up everything in the universe. Color was one of the properties that was not fully understood, as evidenced by the early belief that there were different colored atoms: blue atoms and green atoms and atoms of every color made up the colors of objects that we can see. Isaac Newton was the first person on record to study light and its connection with the colors that we observe. He used prisms to break white light into its component wavelengths. Then, by recombining these component wavelengths, Newton came to understand that all of the colors together made up white light. Our understanding today of how different eyes detect color differently is largely due to early explorations with filters and prisms in ingenious optical setups. Skills Focus Observing, predicting, applying concepts, controlling variables, drawing conclusions Procedure 1. Start Virtual Physics and select Color in Light from the list of assignments. The lab will open in the Optics laboratory. 2. The laboratory will be set up with a garden gnome on an optics table with a detector, or virtual eye, in front of it. The white line on the table shows the direction of the light leaving the object and bouncing into the eye. Observe the image in the Virtual Eye display. 3. Predicting What do you think you will see in the detector window if a red filter is placed between it and the object? Color in Light Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. ISBN 1-269-73240-4 80 Name Date Class Color in Light 4. Observing Filters block all light except the light that is the color of the filter itself. Pick up the filters from the counter and place them in the light path. The gray rectangular part of the piece is the part that needs to be in the light path. The filters flip up into that structure when engaged. Right click on the filters and click the red filter check box. Were you correct in your prediction? What is visible to the eye? Flip the filter in and out and compare the different parts of the gnome to see what happens to the different colors when viewed through the filter. Why do you think some parts of the gnome look black, while other parts, like the pillar, look red? 5. Predicting What colors do you think you will you see if a blue filter is also placed in the light path, in addition to the red filter? 6. If all light but the blue light has been filtered out, and then a red filter is also applied, what color do you think you would see? Right click on the filters and click the red and blue filter check boxes to test your prediction. What do you observe? ISBN 1-269-73240-4 7. Applying Concepts Now pull the filter off the table in any direction to return it to the counter. In the Virtual Eye detector screen you can see checked boxes labeled with the primary colors of red, green and blue. These control the color receptors in the eye. Unchecking any of the boxes turns off the receptors that can detect the chosen colors. Experiment with turning on and off various colors and report your findings about color subtraction. Color in Light 81 Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. Name Date Class Color in Light 8. Colorblindness occurs when certain color receptors in the eye don’t work as they should. Experiment with the two main types of colorblindness: redgreen and blue-yellow, and report how the colorblindness affects the observed colors of the gnome. Select a colorblindness type by checking each of the types in the Virtual Eye detector screen. 9. Controlling Variables Click on the Clipboard on the right hand side of the table to bring up a list of preset experiments. Select Experiment 12: Color Addition and Subtraction. The table is now set up with white light shining through four triangle-shaped prisms to diffuse the colors of the rainbow and a slit control in the center of the table to block out portions of the rainbow before the light is recombined through more prisms. Drag the second prism farther down on the mounted base to spread out the beam of light more. In the Virtual Eye, uncheck the Grid box to be able to see the light beam better. Move the windows, so you can see the display in the Virtual Eye, and the laboratory view at the same time. Change the amount of light passing through the slits by clicking the up and down green arrows on the shutter device. What color do you see when you add just red through yellow? What color results when you combine yellow through blue? What colors do you need to add to produce a light purple? 10. Drawing Conclusions You have been experimenting with color addition and subtraction and the additive primary colors. Explain what happens when you add all of the colors together. Where do you see color addition of light occurring in your daily experience? Color in Light Virtual Physics Lab Workbook, by Brian F. Woodfield, Steven Haderlie, Heather J. McKnight, and Bradley D. Moser. Published by Pearson Learning Solutions. Copyright © 2008 by Pearson Education, Inc. ISBN 1-269-73240-4 82 
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