Question

suppose mercury instead of water was used as the manometer fluid . How would this effect the accuracy of the measurement?

Answer 1

Using mercury instead of water will increase the accuracy . Following are the advantages of using mercury inplace of water as a manometric liquid:

1. Mercury is relatively denser than water, consequently the length of the column of water would have to be about 34 feet high to exert pressure equal to that of the atmosphere while the column of mercury need to be only 30 inches to exert pressure equal to that of the atmosphere.
2. Mercury has a very low vapor pressure when compared to that of water. So it is more sensitive than water to the changes in the atmospheric pressure and rises more quickly to record the changes in the atmospheric pressure.
3. Mercury's freezing point is much lower than that of water's so it can record the atmospheric pressure at temperatures below that of 0 degrees centigrade.
4. Mercury does not evaporate easily so very little mercury vapor enters the vacuum above the mercury in the tube.
5. Mercury being a metal shines brightly and so can be used to read the markings on the tube easily.