486_HW1 - Physics 486 FA07 Homework Set 1 Due Sep 6 2007 1 Blackbody Radiation Radiant energy from the Sun reaches the surface of the earth head-on

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Physics 486 FA07 Homework Set 1 Due: Sep 6, 2007 1. Blackbody Radiation - Radiant energy from the Sun reaches the surface of the earth head-on at a rate of 1.4 kW/m 2 . The radius of the Sun is 7 × 10 8 m and its distance to the earth is 1.5 × 10 11 m. (See class hand-out for Stefan-Boltzmann’s constant, etc.) Terribly off-scale representation of the geometry described above a. What is the power per unit area emanating from the Sun? (Hint: Consider how the intensity of light from a source falls off with distance.) b. What is the surface temperature of the Sun and the wavelength at which it emits the most power? c. Consider the earth to be a perfect blackbody which maintains thermal equilibrium by radiating at the same rate as it receives from the Sun. What is the temperature at the earth’s surface? (You will have to take into account the complication that the area receiving the radiation is a flat disc whose radius is that of the earth while that emitted is from the entire earth’s spherical surface.) Does the answer make sense? If so, why? If not, what is missing?
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This note was uploaded on 09/20/2010 for the course PHYS 486 taught by Professor Staff during the Fall '08 term at University of Illinois, Urbana Champaign.

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486_HW1 - Physics 486 FA07 Homework Set 1 Due Sep 6 2007 1 Blackbody Radiation Radiant energy from the Sun reaches the surface of the earth head-on

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