Assume that the person is wearing only a skimpy bathing suit of negligible area.

Question

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=2.0m and circumference C=0.8m.

For the Stefan-Boltzmann constant use =5.67×108W/m2/K4.

Part A

Take the emissivity to be e=0.6.

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=2.0m and circumference C=0.8m.

For the Stefan-Boltzmann constant use =5.67×108W/m2/K4.

Part A

If the surface temperature of the skin is taken to be Tbody=30C, how much thermal power Prb does the body described in the introduction radiate?

Take the emissivity to be e=0.6.

Explanation / Answer

I am assuming that by the "area of sides of a cylinder" it means the curved surface area of the cylinder. So area of the sides of cylinder is A = CL = (0.8m)(2m) = 1.6m2 which is the area of the human body.

The thermal radiation emitted per unit time by a body of emissivity e, area A and temperature T is given by;

u = eAT4

or u = (0.6)(5.67×108W/m2/K4)(1.6m2)(273 + 30)4

or u = 458.8W

So the human body radiates 458.8W of thermal power.

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