Sir, could you please explain that why does the pitch of sound keep changing as we fill an empty bucket?

PITCH OF THE SOUND DEPENDS ON THE FREQUENCY AT WHICH THE STANDING WAVE IN THE BUCKET WILL RESONATE AND THE FREQUENCY OF STANDING WAVE WILL DEPEND ON THE LENGTH OF THE AIR COULMN IN THE BUCKET .AS ONE FILL THE BUCKET THE LENGHT OF THE A  IR COULMN WILL CAHNGE AND THE FREQUENCY WILL ALSO CHANGE.

 

f=n v/l   where n=1,3,5