1. Describe an experiment to prove that material medium si required for the propagation of sound waves.

To demonstrate that sound needs material medium to travel, take a bell jar with an electronic buzzer placed inside such a way that its electronic terminals are fused in air tight condition through the glass.
The base of the bell jar is hot glued to a hard plate and the base of the plate has an exhaust pipe fitted to a suction air pump ready to draw the air inside.
The electronic buzzer is then switched on and one can hear the sound coming from the bell. This is because the air inside the bell is transmitting the sound waves to the wall of the bell jar which in turn vibrates and transmits the sound outside.
Then exhaust pump is then switched on to draw out the  air. As the air is sucked out of the bell jar, the sound intensity appears to go down outside. Finally, a point comes when no sound is heard from the buzzer although it has been buzzing.
Again when air is let in through the pipe, one can hear sound coming from the buzzer. This proves that sound needs a material medium to propagate.