Measuring Height of Meniscus in Capillary Action

In summary, the conversation discusses capillary action in a tube and the expression of Jurin's Law. The height measured in this law is not from the bottom of the tube, but rather the height difference caused by capillary action. If there was no surface tension, there would be no height difference. The height is measured from different points on the meniscus, and this may vary depending on whether the meniscus is concave or convex. The goal is to determine the surface level of the fluid in the center of the container, and the lowest edge of the meniscus is read for a concave meniscus. The Wikipedia article on the meniscus provides a good overview of this concept.
  • #1
Cogsy
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I've been reading up on capillary action in a tube, and I have some questions:

  1. Say we insert a tube in a pool of fluid; Jurin's Law expression is ##h=\frac{2\sigma \cos \phi}{r\rho g}##. However, this height is not the height of the fluid measured from the bottom of the tube, but rather the difference in height produced by the capillary action. So, if a magical fluid had somehow no surface tension, there would be no height difference between the liquid inside the tube and the one outside of it, am I correct?
  2. From which point in the meniscus do you measure said height? I've seen some authors draw the line up to the curved edge, others to the points where the meniscus makes contact with the tube, and some even do it in between. Also, does said point vary depending on whether the meniscus is concave or convex?
 
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  • #2
The idea is to determine the surface level of the fluid in the center of the container where it's essentially not influenced by the capillary action at the wall surface. So you read the lowest edge of the meniscus as viewed with your eye at the same level (for a concave meniscus).

The Wikipedia article on the meniscus has a reasonable overview.
 

What is capillary action?

Capillary action is the process by which liquids move through narrow spaces, such as tubes or capillaries, due to the forces of adhesion and cohesion.

Why is measuring the height of meniscus important in capillary action?

The height of the meniscus can provide information about the surface tension and viscosity of the liquid, as well as the diameter of the capillary tube. It is also a key factor in determining the rate of capillary action.

How do you measure the height of meniscus in capillary action?

To measure the height of the meniscus, a ruler or graduated cylinder can be used to mark the starting and ending points of the liquid in the capillary tube. The difference between these two points is the height of the meniscus.

What factors can affect the height of meniscus in capillary action?

The height of the meniscus can be affected by the surface tension and viscosity of the liquid, as well as the diameter and material of the capillary tube. Additionally, external factors such as temperature and atmospheric pressure can also play a role.

Can the height of meniscus be used to determine the surface tension of a liquid?

Yes, the height of the meniscus can be used along with other measurements, such as the diameter of the capillary tube, to calculate the surface tension of a liquid using the Young-Laplace equation.

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