During capillary rise of a liquid in a capillary tube, the surface of contact that remains constant is ofa) Glass and liquid b) Air and glass c) Air and liquid d) All of these Correct answer is option 'C'. Can you explain this answer?

Question

During capillary rise of a liquid in a capillary tube, the surface of contact that remains constant is ofa)                                  Glass and liquid                               b)                                  Air and glass                               c)                                  Air and liquid                               d)                                  All of these                               Correct answer is option 'C'. Can you explain this answer?

Answer

During capillary rise of a liquid in a capillary rude the surface of contacts that remains constant is air and liquid.
So option ' C ' is correct answer.

Answer

The confusion is due to the phrasing of the question.
So, let us try to understand the question properly.
1. Imagine a capillary tube.
2. Water is rising inside.
3. Water rising in level implies water is touching more and more of the height of the glass. Hence, the contact of Water with glass is increasing. It is not constant.
Next, as Water level rises, the empty column above filled with air, its volume decreases. That means, the area of surface of Contact between air and glass is reducing. It is not constant.
But, if you look at how Water and the air column are interacting, they are touching (the surface of contact) in the same area. A circular cross-section. It is neither increasing, not decreasing. It remains constant.
Hence, the answer is 'C'
Hope this helps you.

Answer

During capillary rise of a liquid in a capillary tube, the surface of contact that remains constant is the interface between the air and the liquid (option C). This phenomenon is known as capillary action and is governed by the properties of both the liquid and the capillary tube.

Capillary action occurs due to the combined effects of adhesive and cohesive forces. Adhesive forces are the attractive forces between the molecules of different substances, while cohesive forces are the attractive forces between the molecules of the same substance.

Here is a detailed explanation of why the surface of contact between air and liquid remains constant during capillary rise:

1. Adhesive forces between liquid and capillary tube:
- The liquid molecules are attracted to the molecules of the capillary tube due to adhesive forces.
- These adhesive forces cause the liquid to rise in the capillary tube, forming a concave meniscus.
- The shape of the meniscus is determined by the balance between the adhesive forces between the liquid and the capillary tube and the cohesive forces within the liquid.

2. Cohesive forces within the liquid:
- Cohesive forces between the liquid molecules tend to pull the liquid together and minimize its surface area.
- In the case of capillary rise, the cohesive forces cause the liquid to rise higher in the center of the capillary tube, forming a concave meniscus.
- The height to which the liquid rises is determined by the competition between the adhesive and cohesive forces.

3. Surface of contact between air and liquid:
- The interface between the air and the liquid remains constant during capillary rise.
- This is because the adhesive forces between the liquid and the capillary tube are stronger than the adhesive forces between the liquid and air.
- As a result, the liquid is pulled up the capillary tube, maintaining a constant surface of contact with the air.

In summary, during capillary rise, the surface of contact that remains constant is the interface between the air and the liquid. This is due to the balance between adhesive and cohesive forces, with the adhesive forces between the liquid and the capillary tube being stronger than the adhesive forces between the liquid and air.

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