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Wonders of Physics

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Manometer – mercury levels difference changes with different density of liquid used

The pressure of a gas is measured using a manometer as shown in the diagram.


The mercury in the manometer is replaced with a liquid which is less dense. How does the value of h change?

A It becomes zero.

B It decreases, but not to zero.

C It stays the same.

D It increases.

Solutions: Option D

The pressure to be measured remains constant. Since P = pgh, where p is the density of the liquid used in the manometer. If a liquid of lower density is used, height h of the liquid (level difference) will be greater. The gravitational field strength g remains constant.