The emissivity of the human skin is 97.0 percent. Use 35.0 °C for the skin tempe

Question

The emissivity of the human skin is 97.0 percent. Use 35.0 °C for the skin temperature and approximate the human body by a rectangular block with a height of 1.81 m, a width of 39.0 cm and a length of 32.5 cm.

A. Calculate the power emitted by the human body.


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B. Fortunately our environment radiates too. The human body absorbs this radiation with an absorbance of 97.0 percent, so we don't lose our internal energy so quickly. How much power do we absorb when we are in a room where the temperature is 20.0 °C?


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C. How much energy does our body lose in one second?

Explanation / Answer

Total surface area A = 2*(1.81*0.39 + 0.39*0.325 + 0.325*1.81) = 2.8418 m2

Total radiation from body Q = AT4 where is emissivity = 0.97, is constant = 5.67*10-8 W/m2-K4, T is absolute temperature = (35+273) = 308 K

So, Q = 1406.5 W (or 1.4 kW)

This will be the power emitted by the body.

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