question_answer 20)

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

Answer:

  Take an electric bell and an air tight glass bell jar. The electric bell is suspended inside an air tight glass jar which is connected to a vacuum pump. Working : (i) When we press the switch, we will be able to hear the bell. (ii) When the air in the jar is pumped out gradually, the sound becomes feeble although the same amount of current is flowing through the bell. (iii) When the air is removed completely, we will not be able to hear the sound of the bell. Conclusion : This experiment shows that sound requires a medium for its propagation.