Surface tension in capillaries

In summary: The figures below represent capillaries of varying construction and arrangement. The diameter of the capillary portion is the same in each case, and all of the capillaries are constructed of glass, except where otherwise indicated. The equilibrium rise for water is shown at the left. Draw meniscuses in each figure to correspond to (a) the level reached by water rising up the clean, dry tube and (b) the level to which the water would recede after having been sucked up to the end of the capillary. The meniscuses in the capillary may be assumed to be hemispherical in shape.The equilibrium rise for water is shown at the left. Draw meniscuses in each figure to correspond to
  • #1
zircons
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0
The figures below represent capillaries of varying construction and arrangement. The diameter of the capillary portion is the same in each case, and all of the capillaries are constructed of glass, except where otherwise indicated. The equilibrium rise for water is shown at the left. Draw meniscuses in each figure to correspond to (a) the level reached by water rising up the clean, dry tube and (b) the level to which the water would recede after having been sucked up to the end of the capillary. The meniscuses in the capillary may be assumed to be hemispherical in shape. Pay attention to curvatures of meniscus as well.

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a) I think that they the water would just take up the same amount of volume in each tube? I'm confused about the paraffin one though.

b) I don't get this at all.
 
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  • #2
First do you understand why the water goes up the left hand tube?

If you do then see

http://simple.wikipedia.org/wiki/Surface_tension

and compare the contact angle for various materials such a water and glass (0 degrees) and water and paraffin wax (107 degrees).

What happens to the surface tension when the water rising up the glass tube reaches the paraffin wax?

a) Asks about water rising up the tubes. How far does it go? What does the meniscus look like when it stops?
b) Asks what happens if you suck water up the tube and then stop sucking. Clearly the water will sink back down but how far and is the end result the same as in a)? What does the meniscus look like then?

So the answer will be two sets of drawings. Each showing the curve of the meniscus.
 
  • #3
But where I'm confused is that, for example, the water rises up through the paraffin wax tube. But the amount of water makes the paraffin wax contact angle irrelevant because of the wax's location in the middle of the tube. The water rises above it.

Is my reasoning wrong?

For b, I feel like the end result will be the same as in a except opposite (from the other direction).
 
  • #4
But where I'm confused is that, for example, the water rises up through the paraffin wax tube.

Does it? Best start at the beginning..

What makes the water rise up the plain glass tube on the far left at all?
Why does it only rise to that point and no higher?
 
  • #5
Can you please clarify?

I can provide a better understanding of surface tension in capillaries and the figures provided. First, surface tension is the force that holds the molecules of a liquid together at its surface. In capillaries, this force is responsible for the rise and receding of water.

In figure (a), the meniscus at the left represents the level reached by water rising up the clean, dry tube. This is due to the adhesive forces between the water molecules and the glass surface, causing the water to cling to the sides of the tube and rise up. The meniscus is hemispherical in shape, with a convex curvature.

In figure (b), the meniscus at the right represents the level to which the water would recede after being sucked up to the end of the capillary. This is due to the cohesive forces between the water molecules, which causes the water to pull back and form a concave meniscus. The height of the meniscus is determined by the balance between the cohesive and adhesive forces.

In the paraffin tube, the meniscus would be slightly different due to the different surface properties of paraffin compared to glass. However, the same principles of surface tension would apply.

It is important to pay attention to the curvatures of the meniscus as they indicate the strength of the surface tension. A more curved meniscus indicates a stronger surface tension, while a flatter meniscus indicates a weaker surface tension.

I hope this clarifies the concept of surface tension in capillaries and how it relates to the figures provided.
 

1. What is surface tension in capillaries?

Surface tension in capillaries is the attractive force between molecules of a liquid at the surface of the liquid. In capillaries, this force is responsible for the curvature of the liquid at the edges of the capillary walls.

2. How does surface tension affect the movement of fluids in capillaries?

Surface tension plays a crucial role in the movement of fluids in capillaries. It creates a net inward force that pulls the fluid towards the center of the capillary, allowing it to move against gravity and through small spaces.

3. What factors can affect surface tension in capillaries?

Surface tension in capillaries can be affected by several factors, including the type of liquid, temperature, and the presence of surfactants. Higher temperatures and the presence of surfactants can decrease surface tension, while certain liquids may have higher surface tension than others.

4. How is surface tension related to the shape of capillaries?

The shape of capillaries, specifically their small diameter, is directly related to surface tension. The smaller the diameter, the higher the surface tension, as there is a greater curvature of the liquid at the edges of the capillary walls.

5. What are the practical applications of understanding surface tension in capillaries?

Understanding surface tension in capillaries has many practical applications, including in medical fields such as blood flow and drug delivery. It is also important in industrial processes, such as inkjet printing and microfluidics, where precise control of fluid movement is necessary.

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