A manometer reads the pressure of a gas in a enclosure as shown in figure(a) When some of the gas is removed by a pump, the manometer reads as in (b). The liquid used in the manometers is mercury and the atmospheric pressure is `76 cm` of mercury.

(i) Give the absolute and gauge pressure of the gas in the enclosure for cases (a) and (b) in units of cm of mercury .
(ii) How would the level change in case (b) if `13.6 cm` of water are poured into the right limb of the manometer?

Answer

A, B, C, D

Explanation

(i) Absolute pressure in part (a)
`=76cm` of `Hg+20cm` of `Hg`
`=96cm` of `Hg`
Gauge pressure in part (a) `=20cm` of `Hg`
Absolute pressure in part (b)
`=76cm` of `Hg-18cm` of `Hg=58 cm` of `Hg`
Gauge pressure in part (b) `=-18 cm of Hg`
(ii) `13.6 cm` of water is equivalent to `1 cm` of `Hg`. so the new level difference will become `19 cm`.