Answer :
When the capillary tube is shortened to below the height that water rises due to capillary action, the water level adjusts to the new height of the tube and stays at 12cm, corresponding to option b.
The student's question involves the phenomenon of capillary action in physics, which describes the ability of a liquid to flow in narrow spaces without the assistance of external forces. Specifically, the question is about what happens to the water level in a capillary tube when its height is reduced to a level below the height that the water naturally rises due to capillary action.
If the height of the capillary tube is reduced from 18cm to 12cm, which is below the original capillary rise of 16.3cm, the water will not create a fountain nor flow down the sides. The water inside the tube will simply adjust to the new height of the tube, forming a concave meniscus at the top, and stay at a height of 12cm because the force of capillary action can no longer support a column of water higher than the physical height of the tube.
