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exam2009_answers - ATOC/ASEN 5235 Midterm Exam 8 October...

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ATOC/ASEN 5235 Midterm Exam 8 October 2009 All problems are worth 10 points Problem 1 . What are the three main processes by which the atmosphere interacts with radiation? Answer : Emission, Scattering, Absorption Problem 2 : A particular light bulb emits radiation at a wavelength of 500 nm with a power of 10 W. How many photons are emitted each second? Solution: Energy of one photon = E = hc/ λ . Since 1 W = 1 J s -1 : h = 6.625x10 -34 Js c = 3.0x10 8 ms-1 λ = 5.0x10 -7 m hc/ λ = 3.98x10 -19 J # photons per second = 2.51x10 19 Lots of photons!! Problem 3 : In class on 20090903, we derived the equation F = π L, where F is the irradiance (W m -2 ) and L is the radiance (W m -2 sr -1 ). Explain the assumption(s) involved when using this equation. That is, when is it appropriate to use F = π L? I am looking only for a single sentence. Answer: Only if the radiation field is isotropic, and we are considering only the hemispheric irradiance (that is, we integrated over a single hemisphere, not over 4 π sr). Problem 4. Give an estimate for the solar irradiance at the top of the atmosphere of Mars. Answer : The solar irradiance at Earth is 1361 W m -2 . We can use the inverse square law to calculate the irradiance at Mars. Since the Earth-Sun distance is 1 AU, and the Mars-Sun distance is 1.524 AU, the irradiance at Mars is 1361 x (1/1.524) 2 = 586 W m -2 . λ / photon 1 Js 10 photons # 1 - hc s × =
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Problem 5 : Why do diamonds sparkle, often looking like a whole suite of tiny prisms? Answer: This is essentially problem 1 from homework #4. The basic reason is that the critical angle for a diamond/air interface is only 24°. The average index of refraction for diamond in the visible region of the spectrum
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exam2009_answers - ATOC/ASEN 5235 Midterm Exam 8 October...

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