Question

How do changes in atmospheric pressure affect the height of the column of mercury in a barometer?

Answer 1

Well, we know that `1*"atmosphere"` pressure will support a column of mercury that is `760*mm` high.

Explanation:

And thus a mercury column, a mercury barometer, is an excellent means to monitor atmospheric pressure, or pressures LOWER than atmospheric pressure. Mind you, mercury has all but disappeared from laboratories and doctors' surgeries in that (i) it is toxic; and (ii) if you spill the mercury it is very difficult to clean it up.

And the length of the column is proportional to the pressure exerted on the column, i.e. `760*mm*Hg-=1*atm`, `380*mm*Hg-=1/2*atm`. So column length is a good and visual gauge of the pressure.

Of course, daily variations in atmospheric pressure will cause the length of the column to vary. Would the length of the column be the same at altitude? Why or why not?

For a bad example of how this is used in a calculation, see here., and here.