Angle of contact varies between

Options

A. 0 to `pi`
B. `pi//2` to `(3pi)//2`
C. 0 to `2pi`
D. `pi` to `2pi`

Answer

To solve the question regarding the variation of the angle of contact, we can break it down into a step-by-step explanation.

### Step-by-Step Solution:

1. **Understanding Angle of Contact**:
The angle of contact (or contact angle) is defined as the angle formed between the tangent to the liquid surface at the point of contact and the solid surface. It indicates how a liquid interacts with a solid surface.

2. **Case of Water in a Glass Tube**:
When water is placed in a clean glass tube, it tends to rise due to adhesion between the water molecules and the glass. In this case, the angle of contact (θ) is very small, approaching 0 degrees. This indicates that the liquid wets the surface well.

3. **Case of Mercury in a Glass Tube**:
Conversely, when mercury is placed in a glass tube, it does not wet the surface and forms a convex meniscus. Here, the angle of contact (θ) is approximately 180 degrees. This indicates that the liquid does not adhere to the solid surface at all.

4. **Variation of Angle of Contact**:
The angle of contact can vary depending on the combination of the liquid and solid surfaces. It can take values from 0 degrees (complete wetting) to 180 degrees (non-wetting).

5. **Conclusion**:
Therefore, the angle of contact varies between 0 degrees and 180 degrees (0 to π radians).

### Final Answer:
The angle of contact varies between 0 and 180 degrees (0 to π radians).

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