# Rise in mercury level

Tags:
1. Apr 1, 2015

1. The problem statement, all variables and given/known data
A tube which is open at both ends is immersed in a beaker containing mercury. The top end which comes out of the mercury level is now sealed and then the tube is raised by some height such that some part still remains inside the beaker. The mercury inside the tube rises.
Which thermodynamic process takes place?
Why does the mercury inside the tube rise?

2. Relevant equations

none.
3. The attempt at a solution
Initially, let n be the number of moles of air inside the tube. Finally, the number of moles will be the same, since the air inside is sealed.
$$n=\frac{P_0V_0}{RT}$$
As the tube is raised, mercury level inside it rises. The process cant be adiabatic since heat excahange can take place. it could be isothermal but i don't know the exact reason.
As the tube is raised, the volume increases so pressure inside the gas decreases below $P_0$, so the mercury level tends to move due to pressure difference.

2. Apr 1, 2015

### Staff: Mentor

If you are asking whether this is a correct assessment, then yes, it is. You are also correct about the system not being adiabatic so that, when the system re-equilibrates, the temperature will again be the same as the original temperature.

Chet

3. Apr 1, 2015

### Pierce610

Excuse me but, then, is it an isothermal transformation? I think that when we move the tube, the other end immersed exchanges heat, due to friction, with ambient that keeps temperature constant.

4. Apr 1, 2015

### Staff: Mentor

This makes no sense to me. Irrespective of what happens along the way, if you wait long enough, the system will come to equilibrium with the room temperature (i.e., the original temperature).

Chet