To measure liquid pressure, a manometer is used.
Liquid pressure is defined as the increase in the pressure when there is an increase in the depth of the liquid. Liquid pressure is given by the following equation:
|P = ρgh|
- P is the liquid pressure
- ρ is the density of the liquid
- g is the acceleration due to gravity
- h is the depth
Working of manometer
A manometer is used for measuring the liquid pressure with respect to an outside source which is usually considered to be the earth’s atmosphere.
Liquid such as mercury is used for the measurement of the pressure. The other end of the U-tube is filled with the gas for which the pressure needs to be calculated. The end where the gas is filled is sealed while the other end is kept open. Now the atmospheric pressure, as well as the gas pressure, acts on the liquid.
- The air in the tube is said to be equal to the outside air pressure when the liquid is straight level in both the tubes.
- The air in the tube is said to be lighter than the out air’s pressure when the liquid rises above the straight level.
- The air in the tube is said to be heavier than the outside air’s pressure when the liquid is below the straight level.