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lec13 - Lecture 13 Blackbody Radiation Lecture 13 Purdue...

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Lecture 13 Blackbody Radiation Lecture 13 Purdue University, Astronomy 364 1
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Specific Intensity dA Normal d 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
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Mean Specific Intensity Total Intensity (or simply, intensity) Mean Specific Intensity Lecture 13 Purdue University, Astronomy 364 3 I = I ν d ν 0 J ν = 1 4 π I ν d Ω For isotropic radiation, J = I
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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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