Applications of Capillarity

Capillarity, or capillary action, refers to the property of liquid to rise in a capillary tube. The capillary tube here refers to a small passageway or some small cross-sectional area, such as the space between cell fibres or openings in porous materials. Also, while capillary action or capillarity generally refers to rising, it can also refer to a liquid’s depression and is not strictly limited to vertical direction. For example, due to the capillary property of water, it is attracted to the fibres of a towel regardless of its orientation.

Capillarity

Capillarity is created due to surface attraction or interfacial forces. The term interface refers to the surface which separates two phases of matter, and either phase can be solid, liquid, or gaseous. The rise of water in a tube is an example of capillary rise. In this case, the rise of water is caused by the attraction force working between the molecules of water and the glass wall. This force of attraction equates to the gravitational attraction working on the water column and causes the water to reach a specific height. The rise of the water column is directly proportional to the thinness of the tube. It means the narrower the tube is, the higher the water reaches. In contrast to that, the rise of mercury is inversely proportional to the thinness of the tube. It means the narrower the base of the tube, the greater the depression of mercury. The first incident of capillarity was recorded by the great Italian painter and polymath Leonardo Da Vinci. After that, Robert Boyle conducted an experiment on capillarity in 1660, and he documented that partial vacuum had no effect on the rise of the liquid. Later, in 1805, Pierre Simon Laplace and Thomas Young presented a mathematical model of the wicked phenomenon. Later, in 1900, Albert Einstein wrote his first scientific paper on the property of capillary action. Another such example of capillarity is the wicking in the human eye. In this case, the ear duct in the human eye uses capillary action to release excess tears into the nasal passage. Another such example of capillary action or capillarity is the use of tissue paper to wipe up spilled liquid. Also, before donating blood, generally the attendant pricks the finger to collect blood samples to check the iron level in the blood. After that, the blood is placed inside a capillary tube, and the blood rises rapidly inside the tube due to the capillarity of the blood. As, the main component of blood is water, it can be said that the blood is primarily made of water. Another prominent example of capillarity is the process in which plants, even tall trees, can transfer water from the roots through the whole body.

Formula Of Capillary rise

The formula for capillary rise,

h = 2 * T / (r * p * g)

h = height of capillary rise

T = Temperature in Kelvin

r = the radius of the capillary tube

p = density of liquid

g = gravitational force

This formula is applicable to an angle of contact of zero degrees. Otherwise, the formula of capillary rise used is,

h = 2 * T * cos x / (r * p * g)

Where,

h = height of capillary rise

T = Temperature

Cos x = cos value of angle of contact

r = the radius of the base of the tube

p = density of the liquid

g = gravitational force

Capillary action occurs as a combination of two forces. These forces are the cohesive forces induced by the liquid and the adhesive force which works between the liquid and the capillary tube. These two adhesive and cohesive forces are two kinds of inter-molecular forces. These forces actually pull the liquid upwards, causing it to rise. As mentioned earlier, some liquids like mercury behave in contrast to that. Mercury gets depressed by capillary action. This phenomenon is known as convex meniscus.

Capillary force

The term capillary force refers to the interaction between the liquid surface and the solid, and this capillary force causes the liquid to rise inside the tube.

Conclusion

Capillary rise is a basic concept in physics. This is a property seen in the liquid substance by which it can rise inside a very thin tube. This concept is very useful for understanding basic physics, chemistry, and biology and thus is very important for different government exam aspirants.