✔ 最佳答案
No. Your concept and calculations are not correct.
Stefan's Law states that the emission and absorption of thermal radiation is proportional to the fourth power of the absolute temperature.
Since the sun has a surface temperature much much higher than the surroundings, the rate of absorption by an object under the sun is bound to be higher than the rate of emission by the object itself, which is assumed to have initial temperature more or less of that of the surroundings.
For example, assume the surface temperature of the sun is about 6000 K, and the temperature of the surroundings is about 300 K, then
rate of thrmal energy absorbed by an object = k.(6000)^4 watts
rate of thermal energy emitted by the object = k.(300)^4 watts
[where k is a constant, actually it is called the Stefan's constant in physics].
The rate of net heat gained = k[(6000)^4 - (300)^4] watts
But this is only true if the object is a "perfect black body". Practically, objects could not be perfectly black. Hence, a term quantitfying certain percentages of the emission or absorption need to be introduced. This term is called the "emissivity"
Therefore, in general, the rate of net heat gain becomes e.k[(6000)^4 - (300)^4] watts, where e denotes the "emissivity" which has values range from 0 to 1 (a perfect black body has e=1). A black coloured object usually has e close to 1, whereas a white coloured object has low values of e. Hence, black coloured objects have a larger net heat gain than white coloured objects
Your calculation is wrong in the following way,
Black clothes net absorption : 100(80%) - 80 (80%) = 16
White clothes net absorption : 100(20%) - 20 (20%) = 16
When compared with Stefan's Law, the [80] and [20] denote the heat radiated by the object. Since the object is assumed initially of temperature equal to the surroundings, the two values should not differ. Let's assume it be 10, say. Then the calculation should work like this,
2009-11-15 21:57:10 補充：
Black clothes net absorption : 100(80%) - 10 (80%) = 80 - 8 = 72
White clothes net absorption : 100(20%) - 10 (20%) = 20 - 2 = 18
Clearly, black clothes absorb heat far better than whote clothes.
Hope this could clear your concept.
