PHGN341: Thermal Physics
Quiz 2
January 25, 2012
NAME:
1. Consider an ideal gas simulator similar to the Gas Properties PhET. The virtual chamber is 45 nm long and 30 nm
high and has temperature and pressure sensors. You have the choice of filling the chamber with unknown molecules
which are identified as molecule A and molecule B. (1 nm = 10−9 m, kB = 1.38 × 10−23 , 1 amu = 1.66 × 10−27 kg)
(a) You find that if you add 500 molecules of type A into the chamber and adjust the heat you can get standard
temperature (300 K) and pressure (1 atm = 105 Pa). Under these conditions the simulator reports the rms speed
of the molecules to be 419 m/s. What is the mass of the type A molecules in amu units assuming they are diatomic
molecules?
mA =
amu. (Can you guess what the type A gas is composed of?)
(b) You empty the chamber and then launch 500 type B molecules into the chamber and adjust the heat to obtain
standard conditions as before. The simulator reports the rms speed of the molecules to be 1360 m/s. What is the
mass of the type B molecules in amu units assuming they are monatomic?
mL =
amu. (Can you guess what the type B gas is composed of?)
(c) From the above information find the depth, D, of the chamber in nm.
D=
nm.
(d) Based on the kinetic theory of effusion, using your results above what would you expect for the ratio of the effusion
half-lives for the two molecules under the conditions described above?
τB
τA
=
(e) Give one additional test of the kinetic effusion model that you can perform with the ideal gas simulator and explain
how you would go about performing the test and what you would expect from the kinetic theory.
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