# Solutions01 - HOMEWORK 1 Astronomy &amp; Astrophysics...

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Astronomy & Astrophysics – Chapter 8 11a. How much more energy is emitted by a star at 20,000 K than one at 5,000 K? (Assume the sizes are similar.) E = 4 π R 2 σ T 4 E 1 / E 2 = (T 1 / T 2 ) 4 = (20,000 / 5,000) 4 = (4) 4 = 256 X 11b. What is the predominate color of each star in part (a)? Use the Wien displacement law and express your answers in wavelengths. λ max = 0.0029 / T 1 = 0.0029 / 20,000 = 1.45 x 10 -7 m = 145 nm λ max = 0.0029 / T 2 = 0.0029 / 5,000 = 5.80 x 10 -7 m = 580 nm 5a. What is the energy of one photon of wavelength λ = 300 nm? Express your answer both in joules and in electron volts. E = h c / λ = (6.623 x 10 -34 Js) (3 x 10 8 m/s) / (300 x 10 -9 m) = 6.623 x 10 -19 J (/ 1.602 x 10 -19 J/eV) = 4.13 eV 5b. An atom in the second excited state (n = 3) of hydrogen is just barely ionized when a photon strikes the atom. What is the wavelength of the photon if all its energy is transferred to the atom? 1 /

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## This note was uploaded on 11/09/2009 for the course PHYSICS 3021 taught by Professor Staff during the Spring '08 term at Georgia Institute of Technology.

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Solutions01 - HOMEWORK 1 Astronomy &amp; Astrophysics...

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