A vertical glass capillary tube, open at both ends, contains some water. Which of the following shapes may not be taken by the water -in the tube?

Options

A.
B.
C.
D.

Explanation

To determine which shape may not be taken by the water in a vertical glass capillary tube that is open at both ends, we need to consider the forces acting on the water and the nature of surface tension.

### Step-by-step Solution:

1. **Understanding the Setup**:
- We have a vertical glass capillary tube that is open at both ends and contains water.
- The forces acting on the water are gravitational force (weight of the water, \( mg \)) acting downwards and surface tension acting upwards at the water's surface.

2. **Analyzing the Forces**:
- The gravitational force pulls the water downwards, while surface tension tends to pull the water upwards.
- For the water to remain in the tube, these forces must be balanced.

3. **Identifying Possible Shapes**:
- The water can take various shapes depending on the balance of these forces.
- Common shapes include a flat surface, a concave meniscus (curving upwards), or a convex meniscus (curving downwards).

4. **Considering the Shapes**:
- **Flat Surface**: This is possible as the forces can balance out.
- **Concave Meniscus**: This shape is typical in capillary action due to surface tension being stronger than the weight of the water.
- **Convex Meniscus**: This shape is generally not possible in a vertical tube open at both ends because the weight of the water would dominate over surface tension, causing the water to fall rather than form a convex shape.

5. **Conclusion**:
- Therefore, the shape that may not be taken by the water in the tube is the **convex meniscus**.

### Final Answer:
The shape that may not be taken by the water in the vertical glass capillary tube is a **convex meniscus**.

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