Radiation - solving for Q - Stefan-Boltzmann law

AI Thread Summary
The discussion revolves around calculating the radiant energy absorbed by a person's head under two conditions: with hair and bald. The correct formula to use is q = e*sigma*T^4*A*t, where emissivity and surface area are crucial. The initial calculations were incorrect due to a misunderstanding of the area conversion from cm² to m². After correcting the area to reflect that 160 cm² is not equal to 1.6 m², the user arrived at the correct answers for both scenarios. Accurate unit conversion is essential for solving problems involving the Stefan-Boltzmann law.
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Homework Statement



A person is standing outdoors in the shade where the temperature is 27°C.
(a) What is the radiant energy absorbed per second by his head when it is covered with hair? The surface area of the hair (assumed to be flat) is 160 cm2 and its emissivity is 0.85.

(b) What would be the radiant energy absorbed per second by the same person if he were bald and the emissivity of his head were 0.66?

e = .85 for a, .66 for b
sigma = 5.67*10^-8
A = 1.6m squared
T = 300.15K (27 + 273.15)

Homework Equations



q = e*sigma*T^4*A*t


The Attempt at a Solution



By plugging in the known variables, I got

Q/(1 sec) = .85*(5.67x10^-8)*((300.15) ^4)*1.6m squared

Q =625.86 J/s

Q/(1 sec) = .66*(5.67x10^-8)*((300.15) ^4)*1.6m squared

Q = 485.96 J/s


I was told by webassign these answers were wrong. Am I not solving just for Q here? I can't think of any other way besides solving for Q. Also, I'm not sure on the temperature. Do I just take the 27 and convert to kelvin or do I have to do something else? thanks in advance for the help
 
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A meter squared is 100 cm by 100 cm = 10 000 cm².
So 160 cm² is not 1.6 m².
 
Delphi51 said:
A meter squared is 100 cm by 100 cm = 10 000 cm².
So 160 cm² is not 1.6 m².

thank you. By converting it right I got the right answer
 
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