If the angle of contact is less than `90^(@)` the pressure just inside the surface of a meniscus

Options

A. is less than atmospheric pressure
B. is greater than atmospheric pressure
C. is same as the atmospheric pressure
D. None of the above

Explanation

To solve the question regarding the pressure just inside the surface of a meniscus when the angle of contact is less than 90 degrees, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Meniscus Formation**:
- When a liquid (like water) is in contact with a solid (like the glass of a capillary tube), the shape of the liquid surface is influenced by the angle of contact (or wetting angle). If the angle of contact (θ) is less than 90 degrees, the meniscus will be concave upwards.

2. **Identifying Points on the Meniscus**:
- Let's denote two points on the meniscus: Point 1 (just inside the surface of the liquid) and Point 2 (a little lower down in the liquid). The pressure at these points will differ due to the curvature of the liquid surface.

3. **Applying Hydrostatic Pressure Principles**:
- According to hydrostatic pressure principles, the pressure difference between two points in a fluid column can be expressed as:
\[ P_1 = P_2 - \rho g h \]
- Here, \(P_1\) is the pressure at Point 1, \(P_2\) is the pressure at Point 2, \(\rho\) is the density of the liquid, \(g\) is the acceleration due to gravity, and \(h\) is the vertical height difference between the two points.

4. **Relating Pressures**:
- Since Point 2 is lower than Point 1, we can say that:
\[ P_2 > P_1 \]
- This means that the pressure at Point 2 (which is deeper in the liquid) is greater than the pressure at Point 1 (just inside the surface).

5. **Considering Atmospheric Pressure**:
- If we consider the atmospheric pressure \(P_0\) acting on the liquid surface, we can say that:
\[ P_1 < P_0 \]
- This is because the pressure at Point 1 is less than the atmospheric pressure due to the curvature of the meniscus.

6. **Final Conclusion**:
- Therefore, we conclude that the pressure just inside the surface of the meniscus (Point 1) is less than the atmospheric pressure by an amount related to the height difference and the density of the liquid:
\[ P_1 = P_0 - \rho g h \]
- Thus, the pressure just inside the surface of the meniscus is indeed less than the atmospheric pressure.

### Final Answer:
The pressure just inside the surface of the meniscus is less than the atmospheric pressure.

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