Explain that how does an open ended tube manometer measure pressure.

Explanation

An open tube manometer is a simple device.

By this device pressure of gas contained in closed container can be measured.
It cosists of a U- tube containing a suitable liquid. One end of the tube is open to the atmosphere and other end is connected to the system whose pressure we want to measure.
Consider pressure at point A is P.
The pressure P at A is equal to pressure at point B.
`P=P_(B)thereforeP=P_(A)=P_(B)P_(a)+hrhog`
hence `P=P_(a)+hrhog` ...(2)
where `P_(a)` is atmospheric pressure.
h= Height of mercury column from B.
`rho` = Density of liquid.