Q.3. Cite an experiment to show that sound needs a material medium for its propagation.
Divya Prakash Singh
Bell jar experiment showing sound cannot travel in a vacuum:
Take an electric bell and an airtight glass bell jar. 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 gradually, the sound becomes fainter, 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. And finally, when there is no air present inside the jar, there is no sound detectable.
This proves sound needs a material medium to propagate and cannot propagate through the vacuum.