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Physics - Stefan-Boltzman Law

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The star Betelgeuse has a radius r=3.8 x 10^11m. Its surface temperature is 2800K (assume this is 1/2 of that of our Sun). Assuming Betelgeuse is a perfect emitter (e=1.0) what is its power output?
What is the ratio of this power output to the power output of our Sun?

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Stefan Boltzmann constant, sigma = 5.67 x 10^ -8 kg s^ -3 K^ -4.

The power flux from the star is given by F = sigma(T^4) = 5.67 x 10^ -8 x (2800^4)

= ...

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