Question

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

Answer 1

Hint:Bell jar is the equipment that resembles the shape of a bell. This bell jar is provided with an electric bell. Since the sound needs a material medium for its propagation, as the vacuum is created inside the jar, sound cannot travel through the vacuum.

Complete answer:
We know that sound waves are in the form of longitudinal waves since the particles in the medium travel parallel to the propagation of the wave. Sounds can be produced by vibrating bodies such as tuning forks, strings of guitar. Humans produce sound by vibrating the vocal cords.

For the propagation of the sound wave, we have seen that it needs a material medium for propagation. Let’s prove it using the bell jar experiment.

Bell jar is the equipment that resembles the shape of a bell. Let’s connect the base of the bell jar to the vacuum pump via hose pipe. Now, let’s fix an electric bell inside the bell jar and connect it to the supply and close the key. We will hear the continuous ringing of the bell. Now, we turn ON the vacuum pump to draw out the air inside the bell jar. We will observe that the intensity of the sound produced by the electric bell gradually decreases as we continue to draw out the air. After some time, when all of the air inside the bell jar is taken out, there will be total vacuum inside the bell jar. We will not hear any sound of the electric bell even when it's hammer continues to hit the gong.

Therefore, from this experiment we can conclude that sound needs a material medium for its propagation and it cannot propagate through the vacuum.

Note: Vacuum has no particles that can be compressed. Note that light waves that are electromagnetic waves can propagate through air as well as vacuum. It does not require a material medium for its propagation.