Question

Describe the bell jar experiment to prove that sound requires a medium to propagate.

Answer 1

Hint: Here the objective is to demonstrate that sound needs a material medium for its propagation. Bell jar is laboratory equipment. It is used for creating a vacuum. It is named as its shape is similar to that of a bell. Sound is a mechanical wave. For its propagation it needs a material medium like air, water, etc. A sound wave travels in the form of a longitudinal wave. It requires a material medium for its propagation.

Complete solution:
Let's discuss.

Sound originates from some vibrating body. Vibrations are produced by tuning forks, drums, bells,etc. Human voice originates from the vibrations of the vocal cords. The bell jar experiment to prove that sound requires a medium to propagate. It is a laboratory equipment used for creating a vacuum. A bell jar is placed on a base that is vented to a hose fitting and can be connected via a hose to a vacuum pump. The air pressure inside the jar can be varied by pumping the air out of the bell jar.

This experiment is done by placing an electrical bell in the bell jar. The sound from the bell jar fades because the air is pumped out of the sealed bell jar. No more sound is heard from the bell at particular vacuum, but we can see that the hammer continues hitting the gong and sound is produced. Because of the vacuum inside the jar the sound is not audible to our ears. This proves that the sound wave cannot travel through vacuum. Thus the sound wave needs a material medium for its propagation.

Note: We can infer that sound needs a material medium for its travel. The audible frequency ranges from 20 Hz to 20 kHz. The frequency below 20 Hz and above 20KHz is called infrasonic and ultrasonic respectively.