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Homework Help: Radiation: Net Heat Flow

  1. Jun 19, 2017 #1
    1. The problem statement, all variables and given/known data
    What is the net heat flow of an aluminum disk (emissivity = 0.05) with radius
    10 cm and temperature 293K placed inside a room where the temperature is 300K?

    Asurface = π*r2 = 0.01π m2
    2. Relevant equations
    Hnet = A*e*σ(Tradiate4-Tabsorb4)

    3. The attempt at a solution
    By simply plugging in the values, I get a value of 0.13. However, the answer is not among the choices.

    Where did I possibly go wrong?
  2. jcsd
  3. Jun 19, 2017 #2


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    That's the numerical answer that I got (don't forget to include your units in the future), with the possible exception of a negative sign.

    What are the other choices?
  4. Jun 19, 2017 #3
  5. Jun 19, 2017 #4


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    Hmm. The given answer choices differ from our answer by a factor of around √2, for what that's worth.

    Unless there's more to the problem though I think our answer of 0.13 W is correct*. I don't know, maybe it's a mistake in the book/coursework?

    *I'll let you figure out if it's into or out of the disk.
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