Do Incandescent Solids Follow Stefan's Law?

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In summary, the conversation is discussing whether all incandescent solids obey the fourth power law of temperature and if there is a constant value for all temperatures and bodies. It is stated that Stefan's constant sigma has the same value for all temperatures and bodies, but the actual law is I = e*sigma*T^4 where e is the emissivity. It is also mentioned that while sigma remains constant, the emissivity may vary with temperature for a given body.
  • #1
neelakash
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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.

Agreed?
 
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  • #2
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.)
 
  • #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.
 
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  • #4
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.
 

1. What is Stefan's law?

Stefan's law is a physical law that describes the relationship between the total radiation emitted by a black body and its temperature. It states that the total energy radiated per unit surface area of a black body is proportional to the fourth power of its absolute temperature.

2. Who discovered Stefan's law?

Stefan's law was discovered by Austrian physicist Josef Stefan in 1879.

3. How is Stefan's law used in science?

Stefan's law is used in various fields of science, such as astronomy, thermodynamics, and atmospheric science, to calculate the amount of radiation emitted by a black body at a certain temperature. It is also used to study the properties of stars and other celestial bodies.

4. What is the significance of the fourth power in Stefan's law?

The fourth power in Stefan's law represents the relationship between temperature and energy. It means that as the temperature of a black body increases, the amount of energy it emits increases exponentially.

5. Are there any limitations to Stefan's law?

Yes, Stefan's law is only applicable to black bodies, which are theoretical objects that absorb all radiation that falls on them. Real objects, such as stars and planets, do not perfectly follow this law, as they reflect and absorb different amounts of radiation. Additionally, this law only applies to objects in thermal equilibrium, meaning that their temperature is constant.

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