00:01
Okay, so here we've got a question about radiating energy from temperature.
00:04
So we're going to need the stefan boltzmann law, which i've written here at the top in the red box, which is that the power per unit area radiated by an object of temperature t is given by sigma t to the four sigma.
00:20
The stefan boltzman constant of 5 .67 times 10 to the minus 8 watts per meter squared per kelvin to the fourth.
00:26
So the first part of the question says, how much does the human body emit? so we're going to need, it's asking us for the power.
00:37
So power is going to be the surface area of the human body times stefan boltzman constant times temperature to the fore.
00:45
Now it tells us that the temperature is 35 degrees centigrade, which is equal to 35 plus 273 .15 kelvin, which is 308 .15 kelvin.
00:59
Sigma, we've got at the top in a red box.
01:01
And the area, it's asking us to assume that the human body is a rectangular 3d box with height 1 .86 meters, with width 0 .365 meters and with length or depth, 0 .365 meters.
01:26
So you can see that the surface area is going to be 2 times 1 .86 times 0 .36 for the the front and the back surfaces, plus 2 times 1 .86 times 0 .3 for the left and right surfaces here, plus 2 times 0 .365 times 0 .3 for the top and the bottom surfaces.
01:56
Okay, so now we can figure out the power which it would emit if it was ideal, if all the, all the powers or the energy was radiated.
02:12
And this would be a sigma t to the four with all of those numbers as above...