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• The Knudsen regime is the pressure regime in which the mean free path is comparable to the dimensions of the container. (a) Given the container diameter d, the molecule’s collision cross section σ, and the temperature T, derive an expression for the pressure p at which the Knudsen regime occurs. (b) What is this pressure (in atmospheres) for a gas at room temperature (about 293 K) in a container with diameter 20 cm? Assume a molecular radius of 0.15 nm. A good mechanical pump can achieve a pressure of 10−4 atm; can such a pump produce Knudsen pressures in a 20-cm diameter container?
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