Stefan's Law And Definition Of Temperature

[neelakash]

The relation I= $$\sigma$$ $$\ T^4$$ is exact for blackbodies and holds for all temperatures.Why is this relation not used as a basis of a definition of temperature at,say, 100*C?

(i)We do not deal with all black bodies around us.So, for specific objects,we are to put the value of emissivity which is unknown to us.

(ii) T will be a very slowly varying function of Intensity I.The temperature difference of two bodies will be very difficult to find if the total radiation is not tracked.This means,you have to keep track of all the wavelengths...

(iii)The calculation will be cumbersome...

 

[Vazier]

i am not sure if this is the reason but the reason i think stefan's law is not used to define temperature is because it doesn't actually help us understand anything about temperature and also the energy given out by an object in the surrounding due to the difference of temperature depends on the temperature of the body to which it is giving the heat to...

 

[astrokreng]

Thank you for sharing your thoughts on Stefan's Law and its relation to temperature. While it is true that the relation I=σT^4 is exact for blackbodies, it is not practical to use this as a basis for defining temperature at a specific temperature, such as 100°C. This is because:

(i) Not all objects around us are perfect blackbodies, meaning they do not emit or absorb radiation in the same way. This makes it difficult to accurately determine the value of emissivity, which is a crucial factor in the equation.

(ii) In order to accurately measure temperature using this equation, one would need to track all wavelengths of radiation emitted by the object. This would be a very complex and time-consuming task, making it impractical for everyday use.

(iii) The calculation itself would also be cumbersome and require a lot of data and precise measurements, making it difficult to use as a practical definition of temperature.

Therefore, while Stefan's Law is an important concept in understanding the relationship between temperature and radiation, it is not practical to use it as a basis for defining temperature at a specific value. Instead, we use other methods such as measuring the expansion of a substance or the temperature at which a substance changes state, to define temperature at a specific value.