Question

Describe an experiment to prove that a material medium is necessary for the propagation of sound.

Answer 1

A material medium is necessary for the propagation of sound. It can be proved with the help of the following experiment:
An electric circuit consisting of a cell, a switch and an electric bell is arranged inside a bell-jar, which stands on the platform of an evacuating pump.
The switch of the bell is pressed to close the electric circuit. Sound is heard when there is air within the bell-jar. Air is now gradually pumped out of the bell-jar. The intensity of sound goes on decreasing, and no sound is heard when the air is completely removed from the bell-jar. It is because the air which acts as a medium for the propagation of sound energy is removed.

From the above experiment, it is clear that sound can not be heard in the absence of air i.e. a material medium is necessary for the propagation of sound.