- #1

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[itex] B_\nu=\frac{2h\nu^3}{c^2}\frac{1}{e^\frac{h\nu}{k_BT}-1}[/itex]

which has units of total power per unit area of the body, per unit solid angle, per unit frequency (W m

^{-2}sr

^{-1}Hz

^{-1})

Now, how do I find the thermal energy emitted per unit volume? I thought I could just get rid of the unit solid angle by writing

[itex] B_\nu=\frac{8\pi h\nu^3}{c^2}\frac{1}{e^\frac{h\nu}{k_BT}-1}[/itex]

But I am still left with units of W m

^{-2}Hz

^{-1}. Also, does Planck's law even matter for a transparent body, because a black body is completely absorbing? How else would you calculate the true amount of radiated thermal energy?