Question

A bucket kept under a running tap is getting filled with water. A person sitting at a distance is able to get an idea of when the bucket is about to be filled.

What causes the change in the sound?

Answer 1

1. When a bucket is placed under a running tap to fill it with water, a person at a distance is able to hear the sound of water getting shriller.
2. The change in sound is actually caused by the decrease in the length of the air column, thereby, causing a shift in frequency.
3. Since frequency$\left(f\right)$ is inversely proportional to the length of the air column$\left(l\right)$,
   $f\propto \frac{1}{l}$
   On filling water, the air column is decreased, so the frequency of sound increases.

Therefore, the changes in the sound are caused, because the air column is decreased in filling the water in the bucket.