Question

A glass jar contains a liquid of density $\text{'}d\text{'}$ upto a height $\text{'}h\text{'}$at a place where acceleration due to gravity is $\text{'}g\text{'}$, the atmospheric pressure is $P_a$. What is the pressure at the free surface of the liquid?

Answer 1

1. The free surface of the liquid means the top most surface.
2. The pressure at any point at depth h from the surface of the liquid can be defined as, $P=P_{atm}+\rho gh$.
3. Since there is no liquid column above the free surface (h = 0), the hydrostatic pressure will be 0.
4. But the atmospheric pressure will be there.
5. So, pressure at the free surface of the liquid is the atmospheric pressure itself.