I have the following problem I'm trying to solve. Let's say we have a barometer filled with water as in the following diagram:
The question to be answered is what's the pressure $p$ on the inside of the closed upper lid of the tube? The distance from the water surface to the bottom of the barometer tube is $20$ cm.
My reasoning is as follows. Since the hydrostatic pressure given by $$ p = - \rho gh $$ comes from the weight of the fluid above some submerged body, then the pressure $p$ at the top of the tube should be $0$ since there isn't any water above it. I'm not sure if my reasoning is incorrect or if I didn't correctly understand the concepts. Could somebody tell me if my reasoning is correct? Thank you!