Cite an experiment to show that sound needs a material medium for its propagation.
The Bell-jar experiment shows that sound needs a medium for its propagation. An electric bell and an airtight glass bell jar are required. The electric bell is suspended inside the airtight bell jar. The bell jar is connected to a vacuum pump if you press the switch you will be able to hear the bell. Now start the vacuum pump. When the air in the jar is pumped out slowly, the sound becomes dimmer, although the same current is passing through the bell. After some time when less air is left inside the bell jar you will hear a very feeble sound. Now if we evacuate the bell jar no sound is heard.
