Find the pressure of saturated tungsten vapour at a temperature `T = 2000 K` if a tungsten filament is known to lose a mass `mu = 1.2-10^-13 g//(s. cm^2)` from a unit area per unit time when evaporating into high vacuum at this temperature.

Explanation

Here we must assume that `mu` is also the rate at which the tungsten filament loses mass when in an atmosphere of its own vapour at this temperature and that `eta` (of the previous problem) `~~ 1`. Then
`p = mu sqrt((2 pi RT)/(M)) = 0.9 n Pa`
from the previous problem where `p` = pressure of the saturated vapour.