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Theraven1982
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Homework Statement
I have a fairly simple question, but for some reason I can't find the answer. It's about Planck's law, and cosmic background radiation.
We know Planck's law, and we know the temperature of the universe (approx 2.7 K). Furthermore, we know the mean number of photons in a field mode at T.
How much photons per litre does the background radiation contain?
Homework Equations
Planck's law: http://upload.wikimedia.org/math/8/8/5/88585bfa92a0a16aff8f1659935218c3.png"
number of photons excited in a mode at T: 1/(e^{hw/kT}-1)
I've just started following a physics course, after a few years of inactivity...
Any kicks in the right direction are welcome ;).
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