The manometer is basically U-tube containing water. The manometer is used to measure pressure difference or it is used to measure the pressure of a gas. Each of the surfaces is acted upon equally by atmospheric pressure and the levels are the same.

If one side of the manometer is connected to a gas supply, the gas exerts a pressure on the surface A and the level B rises.

The pressure of the gas supply can be calculated from the formula below;

Pressure gas=atmospheric pressure+pressure due to liquid column

P_gas = atm + ρgh

Example: use the information given on the diagram below to answer the following questions:

1. Name the pressure on the surface a and b.
2. Determine the pressure of the gas of atmospheric pressure is 101,000 Pa.

Solution

1. A = pressure of gas

B = atmospheric pressure

2. P_gas = atm + ρgh

But atm = 101,000 Pa,    ρ = 101,000 Pa      g=10m/s²

H = 60cm – 20cm = 40cm

P_gas = 101,000 Pa +13600km/m³*10m/s²*0.40m

        =155,400 Pa

P_gas = 155,400 Pa