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 is in contact with a solid surface (like glass), it forms a meniscus. The shape of the meniscus depends on the angle of contact (also known as the contact angle) between the liquid and the solid.

2. **Identifying the Angle of Contact**:
- The angle of contact is defined as the angle formed between the tangent to the liquid surface and the solid surface at the point of contact. If this angle is less than 90 degrees, it indicates that the liquid wets the surface.

3. **Pressure Considerations**:
- In a liquid column, the pressure at a point is influenced by the height of the liquid above that point and the atmospheric pressure acting on the surface of the liquid.
- Let’s denote the pressure just inside the surface of the meniscus as P1 and the pressure at the surface (atmospheric pressure) as P2.

4. **Applying Hydrostatic Pressure Principles**:
- At the surface of the liquid (point 2), the pressure is equal to atmospheric pressure (P2 = Patm).
- Just below the surface of the meniscus (point 1), the pressure (P1) will be affected by the curvature of the liquid surface.

5. **Relating Pressure and Contact Angle**:
- When the angle of contact is less than 90 degrees, the liquid tends to rise in the capillary tube or wet the surface more, leading to a decrease in pressure just below the surface compared to the atmospheric pressure.
- This is due to the surface tension of the liquid, which creates a negative pressure just below the surface.

6. **Conclusion**:
- Therefore, since P1 (pressure just inside the surface of the meniscus) is less than P2 (atmospheric pressure), we conclude that:
\[ P1 < P2 \quad \text{(or P1 < atmospheric pressure)} \]

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