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hw_7

# hw_7 - ME 125NT Intro to Nanotechnology Due Problem Set 7...

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ME 125NT Intro to Nanotechnology Due: 5/27/2008 1 Problem Set 7 Problem 8.22 in book Solar radiation in the wavelength range of 290-400 nm burns our skin. (a) What range of the electromagnetic spectrum do these wavelengths correspond to? (b) A batch of particles with band gaps ranging from 3.0 to 3.5 eV is prepared for use in sunscreen. What percentage of the harmful wavelengths can this range of particles absorb? Problem 8.31 in book The luminosity of the sun is 3.827×10 26 Watts (1 Watt = Joule/s). This is the approximate power it emits over a range of photon wavelengths, in all directions, out into the solar system. The distance from the earth to the sun is approximately 150,000,000 km (Figure 8.13). The earth’s diameter is 12,756 km. (a) Assuming no photons are absorbed or scattered in the space between the sun and the earth, how much of this power is incident on the earth’s surface? (b) We’ll assume that 40 percent of the sun’s total luminosity is emitted at a wavelength of 550 nm. (This happens to be yellowish light). What is the energy (in Joules) of a single photon with this wavelength? (c) How many photons with this wavelength are incident on the earth every

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hw_7 - ME 125NT Intro to Nanotechnology Due Problem Set 7...

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