In this problem you will consider the balance of thermal energy radiated and abs

Question

In this problem you will consider the balance of thermal energy radiated and absorbed by a person. Assume that the person is wearing only a skimpy bathing suit of negligible area. As a rough approximation, the area of a human body may be considered to be that of the sides of a cylinder of length L=2.0 m and circumference C= 0.8 m. For the Stefan-Boltzmann constant use 5.67*10^-8 W/m^2/K^4 . A) If the surface temperature of the skin is taken to be Tbody= 30 degrees C, how much thermal power Prb does the body described in the introduction radiate? Take the emissivity to be e=0.6 . Express the power radiated into the room by the body numerically, rounded to the nearest 10 W. B) Find Pnet, the net power radiated by the person when in a room with temperature Troom=20degrees C . Express the net radiated power numerically, to the nearest 10 W.

Explanation / Answer

For black body radiation, P(emit) = AseT4 is the emitted power by the body, where s is the S-B constant and e is the emissivity. Remember, T is in kelvin. The power absorbed by the body can be thought of as the power emitted by the surrounding - P(absorb) = AseT(surrounding)4 The difference, P(emit) - P(absorb), is the net power radiated by the person.

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