A berometer correctlu reads the atmospheric pressure as 76cm of mercury. Water droplets are slowly introduced into the barometer tube by a dropper. The height of the mercury column first decreases and then become constant. If the saturation vapour pressure at the atmospheric tgemperature is 0.80cm of mercury, find the height if the mercury column when it reaches its minimum value.

Explanation

Pressure is minimum when the vapour
present inside is at saturation vapour
pressure. As this is the maximum pressure
which the vapour can exert.
Hence the normal level of mercury drops
down by 0.8 cm
:. The height of Hg column
(Given SVP at atmospheric temperature
= 0.08 cm of Hg )
= 76 - 0.80 cm
= 75.2 cm of Hg.