Barometric Pressure

Barometers and Manometers

1. Illustrated below is a mercury barometer. If the height, h, of the mercury column is 0.7535 m, what is the pressure of the atmosphere in atm?

Hint: convert m to mm, then multiply by (1 atm / 760 mm)

2. Illustrated below is a setup for measuring the pressure of a gas. The gas is hooked up to a mercury manometer. Suppose that a perfect vacuum is above the mercury column on the right side and the difference in the height of the columns is 0.1844 m. Calculate the pressure of the gas in cm Hg. 

Hint: Since this is a close-end manometer, the pressure of the gas is simply equal to the difference in the height of the liquid columns

3. Illustrated below is a setup for measuring the pressure of a gas. The gas is hooked up to a mercury manometer; the mercury column on the right side is open to the atmosphere and the difference in the height of the columns is 0.1844 m. Calculate the pressure of the gas in cm Hg if the barometric pressure is 758.4 Torr.

Hint: from the picture, you can tell that the pressure of the gas is higher than the barometric pressure; it pushes down harder on the mercury column.  The difference in the barometric pressure and the pressure of the gas is equal to the difference in heights of the mercury levels.  You add the height of the mercury column to the barometric pressure to get the gas pressure.

4. Illustrated below is a setup for measuring the pressure of a gas. The gas is hooked up to a mercury manometer; the mercury column on the right side is open to the atmosphere and the difference in the height of the columns is 0.1316 m. Calculate the pressure of the gas in cm Hg if the barometric pressure is 758.4 Torr. 

Hint: from the picture, you can tell that the pressure of the gas is lower than the barometric pressure; it does not push down as harder on the mercury column.  The difference in the barometric pressure and the pressure of the gas is equal to the difference in heights of the mercury levels.  You subtract the height of the mercury column to the barometric pressure to get the gas pressure.