Answer:
Put
an electric bell inside a closed glass
jar connected with a vacuum pump.
Initially, air from the jar is not taken out. Connect
the electric bell with a battery as shown in Figure. It rings and the
sound produced is heard by us.
Now start evacuating the air from by the vacuum pump we
will hear lesser sound, i.e., the loudness of the sound decreases. When there
is no air in the glass jar, we do not hear any sound.
This activity illustrates that sound waves require
material medium (in this case air) for its propagation.
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