Lec13 - Lecture 13 Blackbody Radiation Lecture 13 Purdue University Astronomy 364 1 Specific Intensity dA Normal d 8 The amount of power passing

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Unformatted text preview: Lecture 13 Blackbody Radiation Lecture 13 Purdue University, Astronomy 364 1 Specific Intensity dA Normal d 8 The amount of power passing through an element along its normal direction per unit area per unit solid angle per unit frequency range The amount of energy crossing dA with a solid angle d in time dt and in frequency range d is given by dE = I ν ⋅ dA ⋅ dt ⋅ d Ω⋅ d ν Specific intensity or brightness I is in units of J s − 1 m − 2 ster − 1 Hz − 1 Mean Specific Intensity • Total Intensity (or simply, intensity) • Mean Specific Intensity Lecture 13 Purdue University, Astronomy 364 3 I = I ν d ν ∞ ∫ J ν = 1 4 π I ν d Ω ∫ For isotropic radiation, J = I Blackbody Radiation T Imagine a cavity whose wall is heated up to a temperature T. The radiation emitted by the wall is trapped inside the cavity. If the temperature is uniform over the wall, the system is said to be in thermodynamic equilibrium....
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This note was uploaded on 04/23/2011 for the course ASTR 364 taught by Professor Cui,weik. during the Spring '11 term at Purdue University-West Lafayette.

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Lec13 - Lecture 13 Blackbody Radiation Lecture 13 Purdue University Astronomy 364 1 Specific Intensity dA Normal d 8 The amount of power passing

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