1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Please help. Radiation question

  1. Apr 18, 2007 #1
    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


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

    2589399.087 /4186 = total calories

    Answers are wrong
  2. jcsd
  3. Apr 19, 2007 #2


    User Avatar
    Homework Helper

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook