# Stefan's Law And Definition Of Temperature

1. Nov 23, 2007

### 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...

2. Nov 23, 2007

### 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....