Mention two instruments which measure the atmospheric pressure.

When an air bubble rises from the bottom of a deep lake to a point just below the water surface, the pressure of air inside the bubble

During a blood transfusion a needle is inserted in a vein where the gauge pressure is $2000\,Pa$. At what height must the blood container be placed so that blood may just enter the vein ?

[Density of blood $= 1.06 \times 10^3\,kgm^{-3}$ ].

A hollow sphere of radius $R$ is filled completely with an ideal liquid of density $\rho$. sphere is moving horizontally with an acceleration $2g,$ where $g$ is acceleration due to gravity in the space. If minimum pressure of liquid is $P_0$, then pressure at the centre of sphere is

If the atmospheric pressure is $P_a$, then the pressure $P$ at depth $h$ below the surface of liquid of density $\rho $ open to the atmosphere is

There is a circular tube in a vertical plane. Two liquids which do not mix and of densities $d_1$ and $d_2$ are filled in the tube. Each liquid subtends $90^o$ angle at centre. Radius joining their interface makes an angle $\alpha$ with vertical. Ratio $\frac{{{d_1}}}{{{d_2}}}$ is