Question

What is meant by the statement ‘the atmospheric pressure at a place is ’76 cm of Hg'? State its value in Pa.

Answer 1

1. The pressure equal to that exerted by a mercury column of $760mm$ height at sea level is taken as one atmospheric pressure (1 atm).
2. At sea level, the level of mercury in the tube is$76cm$above the level of mercury in the trough. Thus, the pressure equivalent to$76cm(or760mm)$ a high column of mercury is called one atmospheric pressure.
3. 1 atmospheric pressure =$760mm$ of mercury column = $76cm$of mercury column.
4. The SI unit of pressure is pascal$\left(Pa\right).$
5. A pascal (Pa) is defined as the pressure exerted by a thrust of one newton (1 N) acting on the area of one square metre$(1m²).$So $1Pa=1N/m²$
6. Pascal is a smaller unit. So in practice, a bigger unit of pressure called, a bar is used. The bar unit is related to the pascal unit as $1bar={10}^{5}Pa$.