# Homework Help: Question: Radiation of Our body

1. Jun 4, 2006

### cfkorea

Using Stefan-Boltzmann's Law, Determine the quantity of

outgoing energy per unit time from Our Body.

The answer should be of form Watt(W).

You must consider that our body not only radiate but also absorp

energy.

I don't need the exact answer but idea. thanx.

2. Jun 4, 2006

### Dr Transport

What have you done so far???? You have to show some of your prior work.

3. Jun 4, 2006

### cfkorea

This is raw problem.

4. Jun 4, 2006

### Tide

Then show some raw work! :)

5. Jun 5, 2006

### Reshma

:rofl:

cfkorea, is the human body a blackbody?

6. Jun 11, 2006

### bugon

Often, most of the energy lost by the body is not in the form of "black body radiation", but instead through conduction to the air and heat going to evaporate our sweat (latent heat).

Think about it, when it is above 37C outside, we should be heating from the environment, both through radiation and conduction, but instead we still lose the 100-200W we generate.

Incidentally, we're almost all black in the IR (the emissivity is about 0.98 to long wavelength infrared).

Oh, and if you want an answer, simply plug in the numbers to:

$P = A \sigma_{SB} (T_{skin}^4 - T_{environment}^4)$

where A is the effective surface area (about 1 square meter). It is not the nominal 2 because some of the skin faces other parts of the skin and cannot efficiently radiate). $\sigma_{SB}$ is the Stefan-Boltzmann constant. The first term is the energy radiated to the environment while the second is the energy radiated by the environment back to the skin. This assumes a black body. (otherwise, the whole thing would have been multiplied by the emissivity).

– NJS
(http://www.sciencebits.com" [Broken])

Last edited by a moderator: May 2, 2017