Question

Write answers to the following questions.

(a) Give a simple experiment to show that a medium is necessary for the propagation of sound.

(b) How is sound produced in drums?

(c) What is noise?

Answer 1

(a) Take an electric bell and hang this bell inside an empty bell-jar fitted with a vacuum pump (as shown in the figure).

Initially, one can hear the sound of the ringing bell. Now, pump out some air from the bell-jar using the vacuum pump. It will be observed that the sound of the ringing bell decreases. If one keeps on pumping the air out of the bell-jar, then at one point, the glass-jar will be devoid of any air. At this moment, no sound can be heard from the ringing bell although one can see that the prong of the bell is still vibrating. When there is no air present inside, we can say that a vacuum is produced. Sound cannot travel through vacuum. This shows that sound needs a material medium for its propagation.

(b) As we know that vibration is necessary for the production of sound. When a drum is hit by a stick its membrane starts vibrating, and this vibration produces sound.

(c) An excess of unwanted sound in the environment is known as noise. Examples of such noise are loudspeakers and running vehicles.