Ch 05   Homework

(Adopted from Universe, Ch.5, with some modifications)

01. Your normal body temperature is 37℃. What kind of radiation do you predominantly emit? At what wavelength (in nm) do you emit the most radiation?
02. What wavelength of electromagnetic radiation is emitted with greatest intensity by your desk? To what region of the electromagnetic spectrum does this wavelength correspond?
03. Jupiter's moon Io has an active volcano named Pele whose temperature can be as high as 320℃. (a) What is the wavelength of maximum emission for the volcano at this temperature? In what part of the electromagnetic spectrum is this? (b) The average temperature of Io's surface is -150℃. Compare with a square meter of surface at this temperature, how much more energy is emitted per second from each square meter of Pele's surface?
04. The bright star Sirius in the constellation of Canis Major (the Large Dog) has a radius of 1.67 R⊙ and a luminosity of 25 L⊙. (a) What is the energy flux at the surface of Sirius? (b) What is the star's surface temperature?
05. (a) Calculate the wavelength of Hη, the spectral line for an electron transition between the n=7 and n=2 orbits of hydrogen. (b) In what part of the electromagnetic spectrum does this wavelength lie?
06. The wavelength of Hβ in the spectrum of the star Megrez in the Big Dipper (part of the constellation Ursa Major, the Great Bear) is 486.112 nm. Laboratory measurements demonstrate that the normal wavelength of this spectral line is 486.133 nm. Is the star coming toward us or moving away from us? At what speed?
07. The nebula NGC 2363 and its host galaxy NGC 2366 in the constellation Camelopardis (the Camel) are moving away from us at 252 km/s. At what wavelength does the red Hα line of hydrogen (which causes the color of the nebula) appear in the nebula's spectrum?
08. You are given a traffic ticket for going through a red light (wavelength 700 nm). You tell the police officer that because you were approaching the light, the Doppler effect cause the blue shift that made the light appear green (wavelength 500 nm). How fast would you have had to be going for this to be true? Would a speeding ticket be justified? Explain.