Solving an Air Pressure Question: Who Is Right?

[Callmelucky]

Homework Statement

I might be wrong but I think it is author.

Relevant Equations

Pressure= density * g * h

Can someone please answer this question, so I can figure who is wrong here, me or author. Thank you.


1.question (picture below): empty epruvete turned upside down is dipped in glass filled with water to the depth H. While doing that water enters the epruvete and reaches height of h. The AIR pressure inside the epruvete is: I wrote just density(of air) * g(gr. const.)* height(of epruvete - h). The answer is apparently Po(air pressure) + density * g(gr. const.) * (H-h). I am not sure if it's ment density of water or air(since it's not stated), but if they mean density of water I don't understand how is that so, I don't get what water has to do with air pressure inside the epruvete(if pressure = F/A), so please explain if you can/want. Thank you.

But anyway I think that air pressure inside the epruvete should be density(of air) * g(gr. const.) * height(of epruvete - h), if hidrostatic pressure= density * g * height.

Thank you.

 

[BvU]

1. A mercury barometer is a pipe with a closed top that is long enough to have a vacuum above the mercury.

So yes, there is sufficient Hg to fill a column.

2. I have no idea what an epruvete is (google come up with that ?). But from the picture I expect the pipe is not empty at all, but filled with air. There is no Hg here, so they mean the density of water. The pressure at the water level in the pipe is ambient pressure plus some $\rho g \,\Delta h$ :

which I hope you understand by now... ?
( height(of epruvete - h) ... ?)

$\$

 

[Callmelucky]

1. A mercury barometer is a pipe with a closed top that is long enough to have a vacuum above the mercury.

So yes, there is sufficient Hg to fill a column.

2. I have no idea what an epruvete is (google come up with that ?). But from the picture I expect the pipe is not empty at all, but filled with air. There is no Hg here, so they mean the density of water. The pressure at the water level in the pipe is ambient pressure plus some $\rho g \,\delta h$ :
View attachment 321768

which I hope you understand by now... ?
( height(of epruvete - h) ... ?)

$\$

epruvete is test tube, I thought that is the same on all languages(my bad).

Yeah but, in task it's asked for air pressure inside test tube.

It's not a barometer.

 

[Merlin3189]

Edit: Sorry. I didn't read BvU properly. I think he already said this.

Eprouvette is just a test tube. Eprouver = to test (from french)
Presumably filled with air. As pushed into water, air is compressed and stops water rising to outside level.

Level depression is delta h, so internal pressure is just (density of water) x (delta h) x (g) above atmospheric.
IE. just the hydrostatic pressure, because the pressure of the water at the water/air interface in the tube must be that. What's inside the tube is irrelevant.

 

[Callmelucky]

1. A mercury barometer is a pipe with a closed top that is long enough to have a vacuum above the mercury.

So yes, there is sufficient Hg to fill a column.

2. I have no idea what an epruvete is (google come up with that ?). But from the picture I expect the pipe is not empty at all, but filled with air. There is no Hg here, so they mean the density of water. The pressure at the water level in the pipe is ambient pressure plus some $\rho g \,\Delta h$ :
View attachment 321768

which I hope you understand by now... ?
( height(of epruvete - h) ... ?)

$\$

I didn't understand at first, now I do. Thank you for taking time to answer both of my questions.

 

[Callmelucky]

Edit: Sorry. I didn't read BvU properly. I think he already said this.

Eprouvette is just a test tube. Eprouver = to test (from french)
Presumably filled with air. As pushed into water, air is compressed and stops water rising to outside level.

Level depression is delta h, so internal pressure is just (density of water) x (delta h) x (g) above atmospheric.
IE. just the hydrostatic pressure, because the pressure of the water at the water/air interface in the tube must be that. What's inside the tube is irrelevant.

thank you for clarifying,