Question

If the atmospheric pressure is 76 cm of Hg at what depth of water in a lake the pressure will becomes 2 atmospheres nearly.

• A. $862cm$
• B. $932cm$
• C. $982cm$
• D. $1033cm$

Answer 1

The correct option is D $1033cm$

Pressure at that depth $=2$ atmosphere $=2\times 76cm$ of $Hg$

Pressure is due to atmosphere $+$ pressure due to column of

water $=2\times 76cm$ of $Hg$

$⟹76cm$ of $Hg+$ depth $\times$ density of

water $\times g=2\times 76cm$ of $Hg$

Or

$h\times d\times g=76cm$ of $Hg$

Or

$h=76cm\times 13600\times \frac{g}{1000}\times g$

Note: pressure due to $h$ meter of $Hg=h\times densityofmercury\times g$$

Cancelling $g$ we have

$h=13.6\times 76=1033.6cm$ ( as cm is taken for atmosphere answer too comes in cm)