In a capillary tube experiment, a vertical 30 cm long capillary tube is dipped in water. The water rises up to a height of 10 cm due to capillary action. If this experiment is conducted in a freely falling elevator, the length of te water column becomes

Options

A. 10 cm
B. 20 cm
C. 30 cm
D. zero

Answer

To solve the problem, we need to analyze the situation of the capillary action in a freely falling elevator.

### Step-by-Step Solution:

1. **Understanding Capillary Action**:
In a normal scenario, when a capillary tube is dipped in water, the water rises due to surface tension. The height to which the water rises (h) is determined by the balance of forces acting on the water column, including gravity and surface tension.

2. **Given Data**:
- Length of the capillary tube (L) = 30 cm
- Height of water column in normal conditions (h) = 10 cm

3. **Effect of Free Fall**:
When the elevator is in free fall, it is accelerating downwards with acceleration equal to the acceleration due to gravity (g). In this case, the effective gravitational force acting on the water column becomes zero because both the water and the elevator are falling together.

4. **Surface Tension in Free Fall**:
The capillary rise is caused by the balance of surface tension and gravitational force. In free fall, since the effective gravitational force is zero, the water column will not rise due to surface tension. Therefore, the height of the water column in the capillary tube will be affected.

5. **Conclusion**:
In a freely falling elevator, the height of the water column becomes zero because there is no gravitational force acting on the water to counterbalance the surface tension. Thus, the water will not rise at all.

### Final Answer:
The length of the water column in a freely falling elevator becomes **0 cm**.

---