A barometer tube, containing mercury, is lowered in a vessel containing mercury until only $50 c m$ of the tube is above the level of mercury in the vessel. If the atmospheric pressure is $75 c m$ of mercury, what is the pressure at the top of the tube

33.3 k P a

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66.7 k P a

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3.33 M P a

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6.67 M P a

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Solution

The correct option is A $33.3 k P a$
Since the mercury rises only $50 c m$ it implies the rest of the excess atmospheric pressure is being countered by the pressure at the top of the tube.
So pressure at top=atmospheric pressure - $50 c m$ of Hg= $(75 - 50) c m = 25 c m$ of Hg= $1 / 3 \times 100 k P a = 33.33 k P a$

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A barometer tube, containing mercury, is lowered in a vessel containing mercury until only 50cm of the tube is above the level of mercury in the vessel. If the atmospheric pressure is 75cm of mercury, what is the pressure at the top of the tube

The correct option is A 33.3kPaSince the mercury rises only 50cm it implies the rest of the excess atmospheric pressure is being countered by the pressure at the top of the tube.So pressure at top=atmospheric pressure - 50cm of Hg=(75−50)cm=25cm of Hg=1/3×100kPa=33.33kPa

A barometer tube, containing mercury, is lowered in a vessel containing mercury until only $50 c m$ of the tube is above the level of mercury in the vessel. If the atmospheric pressure is $75 c m$ of mercury, what is the pressure at the top of the tube