What is the atmospheric pressure at sea level in millibars (mb)?

A U-tube contains water and methylated spirit separated by mercury. The colunms in the two arms are in level with $10.0 \mathrm{cm}$of water in one arm and $12.5 \mathrm{cm}$ of spirit in the other. What is the specific gravity of spirit?

Explain why,

Atmospheric pressure at the height of about $6 \mathrm{km}$ decreases to nearly half of its value at the sea level, though the height of the atmosphere is more than$100 \mathrm{km}$.

It is known that density $\mathrm{\rho }$ of air decreases with height $y$ as $\mathrm{\rho }=\mathrm{\rho }₀{\mathrm{e}}^{-\mathrm{y}/\mathrm{y}₀}$. Where ${\rho }_0= 1.25 \mathrm{kg} {\mathrm{m}}^{-3}$ is the density at sea level, and ${\mathrm{y}}_0$ is a constant. This density variation is called the law of atmospheres. Obtain this law assuming that the temperature of atmosphere remains a constant (isothermal conditions). Also assume that the value of $g$ remains constant.

Torricelli’s barometer used mercury. Pascal duplicated it using French wine of density$984 {\mathrm{kgm}}^{-3}$. Determine the height of the wine column for normal atmospheric pressure.

During blood transfusion the needle is inserted in a vein where the gauge pressure is $2000 \mathrm{Pa}$. At what height must the blood container be placed so that blood may just enter the vein? ( Take the density of blood to be $1.06 {\mathrm{Kgm}}^{-1}$)