Concept explainers
Iridescent peacock feathers are shown in Figure P27.68a (page 938). The surface of one microscopic barbule is composed of transparent keratin that supports rods of dark brown melanin in a regular lattice, represented in Figure P27.68b. (Your fingernails are made of keratin, and melanin is the dark pigment giving color to human skin.) In a portion of the feather that can appear turquoise (blue-green), assume the melanin rods are uniformly separated by 0.25 μm, with air between them. (a) Explain how this structure can appear turquoise when it contains no blue or green pigment. (b) Explain how it can also appear violet if light falls on it in a different direction. (c) Explain how it can present different colors to your two eyes simultaneously, which is a characteristic of iridescence. (d) A compact disc can appear to be any color of the rainbow. Explain why the portion of the feather in Figure P27.68b cannot appear yellow or red. (e) What could be different about the array of melanin rods in a portion of the feather that does appear to be red?
Figure P27.68 (a) Iridescence in peacock feathers. (b) Microscopic section of a feather showing dark melanin rods in a pale keratin matrix.
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Principles of Physics: A Calculus-Based Text
- A ray is traveling in material a when it reaches an interface with material b, where n < na. If the critical angle for total internal reflection at this interface is erit = 30.0°, what is the ratio of the speed of light in material a to the speed of light in material b, va/v6? O 1.6 O 0.50 O 0.25 O 1.0 O o o oarrow_forward9. A ray of light is emitted beneath the surface of a liquid with air above it. The fluid surface is the xy-plane. The ray emitted from point P(x,y,z) with the coordinates P(-3,0,-4) (in meters) undergoes total internal reflection at point O(0,0,0). What is the index of refraction for the liquid? Draw the ray diagram.arrow_forwardThe sun is 150,000,000 kmkm from earth; its diameter is 1,400,000 kmkm. For a science project on solar power, a student uses a 24-cmcm-diameter converging mirror with a focal length of 51 cmcm to focus sunlight onto an object. This casts an image of the sun on the object. For the most intense heat, the image of the sun should be in focus. The intensity of the incoming sunlight is 1050 W/m2W/m2. What is the total power of the light captured by the mirror? Express your answer with the appropriate units.arrow_forward
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