A.) The emissivity of the human skin is 97.0 percent. Use 35.0 °C for the skin t

Question

A.) 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 1.87 m, a width of 41.5 cm and a length of 26.5 cm. Calculate the power emitted by the human body.

1.371×103 W You are correct.

B.) What is the wavelength of the peak in the spectral distribution for this temperature?

9.40×103 nm You are correct.

C.) 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 27.0 °C?

1370 W incorrect. Hint: Use the Stefan-Boltzmann law again.

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

??? Hint: Calculate the difference between the emitted and the absorbed power. What is the relationship between power, energy and time?

I need help with parts C and D, if you could explain how you got the answers that would be fantastic.

1370 W and 916 W are not correct answers for part C, and 455 J is not correct for part D

Explanation / Answer

Use Stefan's law with an emissivity of 0.97

= 2(0.415 + 0.265) * 1.87 + 2 x 0.415 * 0.265 = 2.76

Radiated power = 0.97 * 2.76 * 5.6704 * 10-8 (273 + 35.0)4 = 1366 W

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C) Absorption by body

= 0.97 * 2.76 * 5.6704 * 10-8 * (273 + 27)4 = 1230 W

D) Body loses = 1366 - 1230 = 136 J

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