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The sketch shows the configuration of a barometer but the fluid is water not mercury. The "pressure of the void" for water is the vapor pressure of water at 80°F. This pressure is about 0.5 psi. Use the schematic.
Calculate the height of the column of water, H.
♦ In the atmosphere at the bottom of the barometer the pressure is atmospheric. An equation relating pressure change from the atmosphere through the water to the water pressure in the void is:
patm - ρwatergoH = 0.5 lbf/in².
14.7(144)lbf/ft2 - ρwatergoH = 0.5(144) lbf/ft²
The above equation contains the single unknown quantity, the height of the column of water. We solve the equation taking proper care of units:
H = 32.8 ft
In principle water can be used in a barometer. However, the height, ~ 33 feet, makes the water barometer impractical in use.