Question

Is it possible to realize whether a vessel kept under the tap is about to fill with water?

Answer 1

Yes. The frequency of a note generated by an air column is inversely proportional to its length. Consequently, as the length of the air column decreases, the frequency increases, i.e., the note becomes more shrill. In our case, when a vessel kept under the top is about to fill with water, as the water level rises, the length of the air column in the vessel goes on decreasing and the emitted sound becomes more and more shrill. Hence it is realised.