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Home Minds On Light Waves and Colors Mission LC5 Color Subtraction Help Help 7

Mission LC5 Color Subtraction

The Question

Three colored spotlights - red, green and blue - with equal intensities may be turned ON and OFF in order to illuminate a shirt with different colors of light. Suppose that a shirt appears yellow when placed under the spotlights. One can say conclusively that the ____ spotlight(s) is/are turned ON.

(Note: the actual colors listed are generated at random and may vary from the above.)

Dig that Diagram

Many students of physics have seen a diagram similar to the one shown at the right. The diagram depicts three circles colored with the primary colors of light - red, green and blue. The primary colored circles overlap to produce other colors of light - known as the secondary colors of light: cyan, magenta and yellow. Complementary pairs of light colors are those colors that are exactly opposite each other on the diagram: red and cyan, magenta and green, and blue and yellow.

Minds On Time

The color a shirt appears is related to the wavelengths (colors) of light that it reflects. And of course to reflect a color of light, that light color must be shining on the shirt. A shirt is placed underneath the red, green and blue spotlights - any one of which could be on or off. The shirt is observed to be of yellow appearance. Yellow light must be reflected by the shirt. Referring to the Dig that Diagram section, yellow light is the combination of red and green light. So if red and green light is being reflected by the shirt, then you know for certain that it must be shining upon the shirt. The red and green spotlights are definitely turned on.

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