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Stefan's law Understanding

  1. Nov 27, 2007 #1
    Do all incandescent solids obey the fourth power law of temperature?

    I think they all obey [tex]\ T^4 [/tex]
    But the constants are different for them.

  2. jcsd
  3. Nov 27, 2007 #2

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    Are you saying that for a particular object, the "constant" remains constant for T=0 to infinity? What logical basis have you for such a conjecture? (Of course, it may not be a conjecture, may be an actual law -- that's what we're discussing here.)
  4. Nov 27, 2007 #3
    Stefan's constant [tex]\sigma[/tex] has the same value for all temperatures and all bodies.

    But the actual law is [tex]\ I= [/tex] [tex]\epsilon[/tex][tex]\sigma[/tex][tex]\ T^4 [/tex]

    where [tex]\epsilon[/tex] is the emissivity.

    I think [tex]\sigma[/tex] is constant for all but [tex]\epsilon[/tex] varies.
    Last edited: Nov 27, 2007
  5. Nov 28, 2007 #4

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    You are correct: sigma is a universal constant.

    For the same body, the emissivity may vary with temperature. So, I = e*sigma*T^4 actually becomes meaningless practically if e varies too much with T for a given body.
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