1. Consider an oven in thermal equilibrium with a photon gas that is inside the oven. Suppose in particular that the oven has green walls, meaning that the walls would look green if illuminated in white light. As you know, an object which looks green in white light reflects more greens and absorbs more of other colors, so it would have a ratio of Ireflected/Io that would look something like the one shown in the figure. (Io represents the initial intensity as a function of energy.)
In your own words, explain the graphs of Iabsorbed/Io and Iemitted/Io. Why do they look as they do, and what's the meaning of them? (This is an illustration of the Kirchhoff Law.)
Enter your answer here:
2. If you assume a human being emits radiation as a blackbody, roughly how many kCal of energy are emitted by your skin per day? (Remember: 1 kCal = 1 "food calorie" = 1000 cal = 4.184 J.)
Comment on the size of your answer -- what's going on here?
3. The cosmic microwave background radiation ("CMBR") has a temperature of about 2.9 K. What is the approximate wavelength at which the CMBR spectrum has its greatest intensity? (i.e., at what wavelength is the peak of the spectral density function?)
Check the correct answer: a) 2 x 10-9 m = 2 nanometersb) 2 x 10-6 m = 2 micrometersc) 2 x 10-3 m = 2 millimetersd) 2 meters Below is a space for your thoughts, including general comments about today's assignment (what seemed impossible, what reading didn't make sense, what we should spend class time on, what was "cool", etc.): You may change your mind as often as you wish. When you are satisfied with your responses click the SUBMIT button.
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