Please help. Radiation question

[owura143]

Suppose the skin temperature of a naked person is 34°C when the person is standing inside a room whose temperature is 25°C. The skin area of the individual is 2.0 m2

a) Assuming the emissivity is 0.80, find the net loss of radiant power from the body

b) Determine the number of food Calories of energy (1 food Calorie = 4186 J) that is lost in one hour due to the net loss rate obtained in part (a). Metabolic conversion of food into energy replaces this loss.


I used

Q/t = emissivity x stefan-boltzmann constant x T^4 x A

= 0.8 X 5.67^-8 X 298.15^4 X 2

=719.277


b) 1 watt per hour = 3600J
total joules = 3600 X 719.277 = 2589399.087


2589399.087 /4186 = total calories


Answers are wrong

 

[mezarashi]

You should become a bit suspicious when you review your calculations and find that the given room temperature of 25 degrees is nowhere to be found!

The question was also framed asking specifically for the "net" loss, meaning, the total power emitted - total power absorbed.

 

[m2003]

.
Thank you for providing the necessary information for me to assist you with this radiation question. I understand that you have calculated the net loss of radiant power from the body to be 719.277 watts and the total calories lost in one hour to be 618.337. However, I would like to point out a few corrections to your calculations.

Firstly, when calculating the net loss of radiant power, it is important to use the difference in temperature between the body and the surrounding environment. In this case, the difference would be 34°C - 25°C = 9°C. Therefore, the correct calculation for the net loss of radiant power would be:

Q/t = emissivity x stefan-boltzmann constant x (T1^4 - T2^4) x A

= 0.8 x 5.67 x 10^-8 x (307.15^4 - 298.15^4) x 2

= 0.8 x 5.67 x 10^-8 x 463916.65 x 2

= 0.664 watts

Therefore, the net loss of radiant power from the body would be 0.664 watts.

Secondly, when converting from watts to joules, it is important to use the correct unit conversion factor. 1 watt per hour is equal to 3600 joules, not 1 watt per hour = 3600J. Therefore, the correct calculation for the total joules lost in one hour would be:

Total joules = 3600 x 0.664 = 2390.4 joules

Finally, when converting from joules to calories, the correct unit conversion factor is 1 calorie = 4.186 joules, not 1 food calorie = 4186J. Therefore, the correct calculation for the total calories lost in one hour would be:

Total calories = 2390.4 / 4.186 = 571.7 calories

Therefore, the total number of food calories lost in one hour due to the net loss of radiant power from the body would be approximately 572 calories.

I hope this clarifies any confusion and helps you to obtain the correct answers. If you have any further questions, please do not hesitate to ask.