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A barometer reads 75cm if mercury. When ...

A barometer reads 75cm if mercury. When `2.0cm^(3)` of air at atmospheric pressure is introduced into space above the mercury level, the volume of this space becomes `50 cm^(3)`. find the length by which the mercury column descends.

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Let the pressure of the air in the barometer be p. We have ,
`pxx50cm^(3)=(75cm of mercury)xx(2.0cm^(3))`
`p=3.0cm` of murcury.
The atmospheric pressure is equal to the pressure due to the mercury column plus the pressure due to the air inside, Thus, the mercury column descends by `3.0cm`.
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