The open-tube manometer is another device that can be used to measure pressure. The open-tube manometer is used to measure the pressure of a gas in a container.
The pressure of the gas is given by h (the difference in mercury levels) in units of torr or mmHg. Atmospheric pressure pushes on the mercury from one direction, and the gas in the container pushes from the other direction. In a manometer, since the gas in the bulb is pushing more than the atmospheric pressure, you add the atmospheric pressure to the height difference:
Pgas > Patm Gas pressure = atmospheric pressure + h (height of the mercury)
Pgas < Patm Gas pressure = atmospheric pressure - h (height of the mercury)
You could be asked about a
closed-tube manometer. Closed-tube manometers look similar to regular manometers except that the end that’s open to the atmospheric pressure in a regular manometer is sealed and contains a vacuum. In these systems, the difference in mercury levels (in mmHg) is equal to the pressure in torr.
