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Idea: It is possible to measure pressure by relating pressure
differences to the variation in the height of a column of liquid.
for measuring pressure are:
1. Open-tube manometer
The pressure P of the gas in the closed cylinder on the left in fig.9.5 is related to atmospheric pressure P0 (exerted on the top of the column of liquid on the right) by:
|P - P0 = gh||(11)|
P absolute = P gauge + P0.
2. Mercury Barometer
Atmospheric pressure is measured by ensuring that the pressure at the closed end of the barometer tube in Fig.9.6 is zero (i.e. it is vacuum). Thus
|P0 = gh||(12)|
It turns out that the pressure of 1 atmosphere (1 atm), is equivalent to a column of mercury exactly 0.76 m high at a temperature of 0 o C with g = 9.80665 m/s 2 and = 13.595 x 103 kg/m 3. From this information, we conclude that
|1 atm = 1.013 x 105 Pa = 101.3 kPa.||(13)|