Tag: fluids

The atmospheric pressure decreases by $1cm$ for every $125m$ increase in height.

No, it doesn't depend on the cross-section of the tube.

An aneriod  barometer is made up of a vacuum chamber covered by a thin elastic disk. High atmospheric pressure pushes against the disk and causes it to bulge inward, while low pressure does not push as hard, allowing the disk to bulge outward.

Fortin's barometer is used to measure atmospheric pressure. It is a modified form of Torricelli's simple barometer.

The word 'aneroid' means dry. They are called dry because they do not use any fluid in them. They work on the bulging and compression of diaphragm.

The first reason to use mercury is its high density. The atmospheric pressure measured by mercury barometer is the pressure equal to that at the bottom of the mercury column given by $h\rho g$.

'Aneroid' means dry. Aneroid barometers are those barometers that do no require any fluid to work and measure atmospheric pressure. Hence they are called dry barometers due to this absence of any fluid(specially liquid).

Mercury is the heaviest liquid. Therefore, it rises only to a height of $76cm$ to balance the atmospheric pressure. Water, being $13.6$ times lighter than mercury, will rise to a $13.6$ times larger height. So, the glass tube needs to be much longer.

True. Mercury is used as barometric liquid because it does not vaporise under vacuum condition.

Fortin's barometer is widely used in laboratories and in meteorological departments. Main advantage of Fortin's barometer is it is portable and it allows the mercury level in the cistern to be set to zero. this makes the reading move accurate.