Question

Atmospheric pressure at a certain place is equivalent to $78cm$ of mercury. That place is

• A. $250m$ above sea level
• B. $250m$ below sea level
• C. $125m$ above sea level
• D. at the sea level

Answer 1

The correct option is B $250m$ below sea level

Atmospheric pressure at that place is $78cm$ of mercury.
We know that the atmospheric pressure at the sea level is $76cm$ of mercury.
This means, this place has an atmospheric pressure $(78-76)cm=2cm$ more than the atmospheric pressure at the sea level.
We know that the atmospheric pressure increases by $1cm$ for every $125m$ decrease in height.
So, this place is $(125\times 2)m=250m$ below sea level.