[net.physics] Stefan's Law of Radiative Cooling

wasser_1@viking.DEC (John A. Wasser) (05/07/85)

>>
>>	Consider that if you were at f1 and looked in any direction
>>	you would see black-body radiation that depended on the
>>	temperature of f2.   If f2 is colder than you, you would
>>	loose heat to it by radiation.  If f2 is hotter than you
>>	you would gain heat from it.  If f2 is the same temperature
>>	as you, you would neither loose nor gain.
>
> There is an appeal to fuzzy thinking here.
>
	What fuzzy thinking?  According to my physics book "Heat energy
	flows spontaneously from hot objects to cooler objects but not
	vice versa." and they give the formula:

		(delta Q) / t = K (T1**4 - T0**4)

	(delta Q)/t  is the ammount of heat lost by radiation per unit time
	K            is some positive constant
	T1           is the temperature of the hot object
	T0           is the temperature of the 'surroundings' (in this 
	             case, the other object)

	This formula is called Stefan's Law and it is clear that an
	object hotter than its surroundings will loose heat to its
	surroundings in a quantity proportional to the difference
	in the fourth power of the respective temperatures.

	In short, the hotter object will loose heat and the cooler
	object will gain heat until the two objects are the same
	temperature.  At that point (T1 .eq. T0) the transfer of
	heat energy stops.

	I'm sorry I didn't put all this information in the original
	post... I thought the readers of net.physics would know
	this stuff.

		-John A. Wasser

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