A capillary tube 20 cm long is dipped in water and water rises to 8 cm inside it. If the whole setup is placed in a freely falling lift (free fall), what will be the length of the water column in the tube?

8 cm
10 cm
4 cm
20 cm

Correct answer: 20 cm

Solution

Capillary rise h is inversely proportional to g. In free fall, effective g = 0, so the capillary force is no longer balanced by gravity and water rises to fill the entire available tube. Since the tube is 20 cm long, the water column becomes 20 cm (it cannot overflow as a continuous spout in this idealized result).

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