Give an experiment to show that sound needs a material medium for its propagation.

Solution:
Take an electric circuit which consists of a power supply source, a switch and an electric bell arranged inside a bell jar, which stands on the platform of a vacuum pump. The switch of the bell is pressed to close the electric circuit. When there is air within the bell jar, sound is heard. Air is now pumped out of the bell jar. When the air is completely removed from the bell jar, no sound is heard because the medium of air which has to carry sound from the bell to the bell jar, is removed. It shows that sound needs material medium for its propagation.