Capillary Action Homework: ΔP, γ, R1, R2

AI Thread Summary
The discussion revolves around understanding capillary action and the Young-Laplace equation in the context of fluid mechanics. It highlights the behavior of water and mercury in capillary tubes, noting that water forms a concave meniscus due to adhesion, while mercury forms a convex meniscus due to stronger cohesive forces. The question also addresses the application of the Young-Laplace equation, particularly regarding the interpretation of radii of curvature when dealing with parallel plates. The poster seeks clarification on how to calculate pressures above and below the meniscus and whether rearranging the equation is appropriate. Overall, the conversation emphasizes the complexities of capillary action and the need for further guidance on applying theoretical concepts to practical scenarios.
MFAHH
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Homework Statement



Kindly view the attached.

Homework Equations



ΔP = γ(1/R1 + 1/R2)

The Attempt at a Solution


[/B]
I've began the topic of fluid mechanics, capillary pressure, surface tension and such and was given this question to try. Now from my limited knowledge it seems to me that in the case of the liquid being water, a concave meniscus will be formed due to the water's adhesion to the inner plate walls (due to the water's polarity) and this will result in upwards capillary action. As for the case in which the liquid is mercury, the greater cohesive force between the mercury and the walls will cause the height of the mercury between the plates to drop lower than the surface of the mercury outside, and the mercury will form a convex meniscus. Is this correct?

For the second part of the question, the young-laplace equation as given is in terms of two radii of curvature, but since we are dealing with plates, would I be right in thinking that it only has a single radius of curvature (the distance between the plates) and the other would be undefined (due to their being no definite end to plates in the direction parallel to them)? How this comes into play, and how to calculate the pressure above and below the meniscus, I'm not too sure on though. Can anyone please give some help?

Much appreciated.
 

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Anyone?
 
MFAHH said:

The Attempt at a Solution


[/B]
As for the case in which the liquid is mercury, the greater cohesive force between the mercury and the walls will cause the height of the mercury between the plates to drop lower than the surface of the mercury outside, and the mercury will form a convex meniscus. Is this correct?

http://en.wikipedia.org/wiki/Meniscus
 
SteamKing said:
http://en.wikipedia.org/wiki/Meniscus

Awesome, so from what I read there I'm more or less on the right track. As for the next part of the question, how is it that I am meant to proceed? Is it just that I rearrange the young Laplace equation for the pressures above and below? But then that answer won't be in terms of what I know from the question.
 
:oldconfused:
 
Anybody? :)
 

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