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# final2009_answers - ATOC/ASEN 5235 Cumulative Exam 10...

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ATOC/ASEN 5235 Cumulative Exam 10 December 2009 1. (5 points). In round numbers, the human body temperature is about 100°F. What is the wavelength of our maximum thermal emission? Answer: Wien’s law tells us that the wavelength of maximum emission is given by: λ max ~2897 / T where T is in degrees K and the wavelength is in units of μ m. Convert 100°F to K: deg K = (100 – 32) / 1.8 + 273 = 311 K. λ max = 2897/311 = 9.3 μ m 2. (5 points). Rank the following transitions from lowest energy to highest energy: rotation, vibration, electronic. 3. (5 points). Mark the following statement as true or false, and explain your answer: If I take a photograph of a clear, blue sky about 10° above the northern horizon at sunrise on 21 September, with a linear polarizer that only transmits vertically polarized light, the sky will appear dimmer than if I were to use a linear polarizer that only transmits horizontally polarized light. Answer: False. The Rayleigh scattered light from the sky at 90° from the sun, which is the situation described, will be vertically polarized. This is because its original horizontal component is in the direction of propagation from the horizon to your camera, which means it must be extinguished when the radiation is scattered toward your camera. Thus the radiation will be transmitted through the vertical polarizer. If you were to use a horizontal polarizer, the sky would appear dimmer because it would not transmit the vertically polarized scattered light. 4. (5 points). (a) Draw a diagram that shows sunlight being scattered at a 30° scattering angle. (b) Is this forward or backward scattering? 5. (10 points). Define “emissivity” and “absorptivity”, and give a statement of Kirchhoff’s Law. Use words, not mathematical equations. Answer: Emissivity is the amount of radiation emitted by an object relative to the amount emitted by a blackbody at the object’s temperature.

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final2009_answers - ATOC/ASEN 5235 Cumulative Exam 10...

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