Question:
The height of a mercury column in a barometer in a Calcutta Laboratory was recorded to be $75 \mathrm{~cm}$. Calculate this pressure in SI and CGS using the following data: Specific gravity of mercury $=13.6$, Density of water $=1000 \mathrm{~kg} / \mathrm{m}^{3}, \mathrm{~g}=9.8 \mathrm{~m} / \mathrm{s}^{2}$ at Calcutta. Pressure $=\mathrm{h} \rho \mathrm{g}$ in usual symbols
Solution:
$\mathrm{H}=75 \mathrm{~cm}$, density of mercury $=13600 \mathrm{~kg} / \mathrm{m}^{3}, \mathrm{~g}=9.8 \mathrm{~ms}^{-2}$ then, pressure $=10^{5} \mathrm{~N} / \mathrm{m}^{2}$.
In C.G.S. units, $P=10 \times 10^{5}=10^{6} \mathrm{dyne} / \mathrm{cm}^{2}$