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Blackbody problemby Sneil
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#1
Oct405, 10:18 PM

P: 18

Hi, im having trouble with the last question in my assignment. It's on blackbody radiation and total power per area and whatnot. those questions i was able to do fine, however when i came to this problem i was a little lost..
here it goes, i'll type the whole thing out.. "The most important energy source in so called main sequence stars is fusion of four protons into He nuclei. A star has a radius r How many he nuclei does the star produce per second if He production is the dominant energy source? Use the Q value for the conversion 4H >He to estimate the amount of raditation energy generated by hydrogen burning, and assume that the radiation energy output per second corresponds to the energy generated by hydrogen burning in a second." any help would be greatly appreciated. thanks Neil 


#2
Oct505, 02:17 AM

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P: 6,653

You appear to be missing an essential piece of information: the surface temperature of the star. Without that, it is not possible to answer the question. AM 


#3
Oct505, 03:51 AM

P: 10

through Carbon Nitrigen Oxygen cycle Well I can't remeber whole thing but you can find it in any text book. Also a minimum temperature is required at core for this process ro take place But surface temperature would be much lesser 


#4
Oct505, 08:11 AM

P: 18

Blackbody problem
sorry, i calculated surface temp to be 4990k
the question says turns to He (of atomic mass # 4) i was just hoping for a formula i would be able to work with as i don't kow where to begin, but ill give the radius too if you want all the info. r=7.02*10^8 m anyone able to help this early in the mourning? thanks for the help, it is greatly apreciated Neil 


#5
Oct505, 08:54 AM

Admin
P: 21,827

To be in equilibrium, the energy production in the star must equal the energy radiated, so
E_{gen} = E_{rad}. E_{gen} = Number of reactions * Q_{reaction}. and one should have a formula for blackbody radiation, the StefanBoltzmann law E = ([itex]\sigma T^4[/itex]) *A. For He can be produced from 4 protons indirectly by the PP or CNO cycles. http://csep10.phys.utk.edu/astr162/l...y/ppchain.html http://csep10.phys.utk.edu/astr162/lect/energy/cno.html or more generally http://csep10.phys.utk.edu/astr162/lect/index.html 


#6
Oct505, 09:05 AM

P: 18

thanks man, im a little lost as to how i incorporate the radius, but ill figure it out
thanks 


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