Physics bell jar question?

Question

Please look at the diagram below

http://i71.photobucket.com/albums/i159/JogaBonito7/DSC00560.jpg

Some students set up an experiment as shown in the diagram. However, no matter what they tried, they could always hear the ringing of the bell.

(1) What was the aim of the experiment?

(2) Give one possible reason for the lack of success.

Answer 1

The aim of this experiment is to remove air from the bell jar, thus providing no medium for the sound vibrations to travel through, as a vacuum is generated.

However, not all of the air can be successfully removed, as the joints of the apparatus are unlikely to be fully secure.