Question

Give four reasons for using mercury as a barometric liquid in a simple barometer.

Answer 1

The main reasons for using mercury as a barometric liquid in a simple barometer are discussed below:

1. Mercury does not evaporate under the vacuum conditions and hence the mercury column in the barometer represents the true atmospheric pressure.
2. At ordinary temperatures, the vapour pressure of the mercury is negligible and therefore the mercury column in the barometer represents the true atmospheric pressure.
3. Mercury being extremely dense counter-balances the atmospheric pressure easily in the barometer which is not possible in less dense liquids such as water and alcohol.
4. Mercury can be easily obtained in the pure state and hence we can easily record the true atmospheric pressure because the pressure is directly proportional to the density of the liquid.
5. Mercury being opaque and shiny is easily visible in the glass tube.
6. In mercury, the cohesive forces predominate the adhesive forces, and therefore mercury does not wet the sides of the glass tube which ensures a correct reading.