A barometer tube is 80 cm long (above the mercury reservoir). It reads 76 cm on a day. A small amount of water is introduced in the tube and the reading drops to 75.4 cm. Find the relative humidity in the space above the mercury column if the saturation vapor pressure at the room temperature is 1.0 cm.

Question

Philoid · Accepted Answer

The reading of barometer gives the pressure in cm of Hg

Given

Reading of barometer on a day= atmospheric pressure of that day P= 76cm of Hg=0.76m of Hg

Drop in pressure when water is introduced P’=75.4cm of Hg

=0.754m of Hg

So, vapor pressure =P-P’=0.76-0.754=0.006m of Hg

Given saturation vapor pressure = 1cm of Hg=0.01m of Hg

So

the relative humidity in the space above the mercury column is 60%.