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Radiation pressure vs air pressure

  1. Dec 3, 2013 #1
    1. The problem statement, all variables and given/known data
    Consider the electromagnetic radiation inside a kiln, with a volume of 1 m3 and a temperature of 1500 K.

    Calculate the radiation pressure inside the kiln. How does it compare with the air pressure?

    2. Relevant equations
    PV = NkT

    3. The attempt at a solution
    I got the total energy using U/V = 8π5(kT)4/15(hc)3 and got U = 3.83 kJ. To find the radiation pressure would I just divide the energy by c? Also, how do I find the air pressure if I don't have a value for N?
  2. jcsd
  3. Dec 4, 2013 #2
    Radiation pressure is related to the energy density, not total energy. If you don't have a formula at hand, you can calculate the relation pretty easily by using for instance [tex]C_v = \frac{\partial U}{\partial T} = T\frac{\partial S}{\partial T} [/tex] to find entropy. Use that to find the free energy [itex] F = U - TS [/itex] and pressure [itex] p = -\frac{\partial F}{\partial V} [/itex].
  4. Dec 4, 2013 #3
    Thanks!, this helps a lot
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