The following Experiment Clearly shows that sound requires a medium to propagate.
● Take an electric bell and an airtight bell jar.
● Suspend the bell inside the bell jar.
● Connect a vacuum pump to the bell jar as shown in the figure.
● Press the switch to hear the bell.
● Now, start the vacuum pump.
● When the air in the jar is pumped out gradually, the sound becomes fainter even though the same current is passing through the bell.
● As the amount of air decreases inside the bell jar, the sound becomes fainter.
● When there is no air inside the jar, there is no sound of the bell. This shows that sound requires a medium to propagate.
