List of substances impervious to air other than cork?
I have Physics presentation where i want to show that sound needs a medium to travel.Hence, i thought of putting a bell in a glass jar(there is no air in it as i would have burnt a piece of paper in it) and closing it with a cork...However, i cannot find a glass jar that's big enuff for the bell to fit yet small enuff for a wine cork...PLEASE suggest some other substances that are impervious to air other than cork!!!
As a former teacher, I can tell you that there is a standard apparatus for this demonstration. It consists of a bell shaped jar which you put on a greased plate to seal it. It is all attached to a vacuum pump to remove the air. The bell is dangling in the jar with small wires attached to rods that exit the grease sealed rubber bung.
The burning paper idea will not work.. a] it goes out before all the oxygen is used and b] it replaces it with another gas, carbon dioxide which also conducts sound. For the experiment to succeed you need a pretty good vacuum or you'll still hear the bell. .. I used to run a good vacuum pump for nearly a minute to achieve good results. The bell jar must be a suitable thick walled one for the purpose or it'll will implode. It needs a metal gauze surround and safety screen anyway.
It will never be totally silent as some sound will be conducted via the electrical wiring and you can never get a 100% vacuum with a school vacuum pump. However, done properly, this expt is very effective and will demonstrate with idea OK.
Incidentally, I can't understand why you put this question in the chemistry section when you say it is physics!!! Science is all about care and attention to detail.
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