Question

Part 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 1.56 m, a width of 38.5 cm and a length of 33.5 cm. Calculate the power emitted by the human body.   

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 23.5 °C?   

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

Answer 1

Part A) Given, the emissivity of human skin is,

Temperature of the skin,

Height of the Human body,

Width of the Human body,

Length of the HUman body,

Therefore the total surface area of the body is,

The power radiated by the body can be calculated by using Stefan-Boltzmann Law, which is given by

where is the Stefan-Boltzmann Constant, where

here all the terms in are constant, where is the Boltzmann constant, is the speed of light in vacuum, is the Planck's constant.

Therefore Power radiated by the body can be found out as,

substituting the all the values,

Therefore power emitted by the human body is

Part B) We can again calculate the power emitted in an enviroment having temperature,

Stefans-Boltzmann law will be

Therefore the power emitted in this environment will be .

Since power will be emitted in this environment compared to earlier case, which is .

Reduction in emission of power is,

Therefore is there in the environment for the body to absorb,.

Also the absorbance of the body is,

Absorbed Power,

Power absorbed in the room at , is .

Part C) Power radiated by the body at is which is

Therefore our body loses energy in one second at .