Texts: Question 3:
The air in the classroom is composed of 77.768% N2, 20.861% O2, 0.930% Ar, 0.041% CO2, and 0.4% H2O vapor. The number density of N molecules in the room is n(N) = 1.9741025 m^(-3).
a. Estimate the number density of H2O molecules, n(H2O), in our classroom in units of m^(-3).
b. H2O has a molecular absorption band at a wavelength of λ = 6.3 μm with an absorption cross-section σ = 8.010^(-2) m^2. What is the mean free path of a λ = 6.3 μm photon in our classroom? Express your answer in appropriate units (km, m, cm, mm).
c. You are seated at the back of the classroom, and the projector screen at the front is 10 meters away. Could you see what is being projected on the screen if you were wearing infrared goggles that only let you see 6.3 μm wavelength light? Be quantitative.
d. The chairs in the room are spaced about 2 meters apart (COVID distancing measures). Could you see the person sitting in the chair immediately in front of you when wearing 6.3 μm goggles? Be quantitative.
e. Human skin temperature is about 28°C, while the room air, walls, and furniture are about 25°C. What is the typical wavelength of light emitted by objects of this temperature? Describe in words what our classroom would look like with all 35 students in attendance if you were wearing 6.3 μm infrared goggles, given what you just computed for parts b through d.
