# Question about a mercury barometer with an imperfect vacuum

by guitarstorm
Tags: barometer, imperfect, mercury, vacuum
 HW Helper PF Gold P: 3,440 Let's forget about numbers for the time being and let's set up an equation balancing pressures. pair+ρHggh1=ρHggh10 (h1=29.80", h10=29.90"). Now use the ideal gas law to write $p_{air}=\frac{NkT}{A(h-h_1)}$ where A is the cross-sectional area of the column. Replace in the pressure balance equation. Write a second such equation for the second set of given pressures. Once you do this, observe that you have a system of two equations and two unknowns, h and NkT/A. Find them and use them in the third pressure balance equation. On edit, I add that the assumption here is that the temperature stays constant.