Lakhmir Singh Solutions Class 9 Physics Solutions for Exercise in Chapter 5 - Sound

Question 61 Exercise

a) An electric bell is suspended by thin wires in a glass vessel and set ringing. Describe and explain what happens if the air is gradually pumped out of the glass vessel.

b) Why cannot a sound be heard on the moon? How do astronauts talk to one another on the surface of the moon?


a) When the air is gradually pumped out of the glass vessel, the ringing of the electric bell cannot be heard as there is a creation of a vacuum inside the glass vessel. As there are no air molecules inside the glass jar, sound waves cannot travel.

b) Sound cannot be heard on the moon because there is no air on the moon which acts as a carrier of sound waves. Astronauts talk to one another with the help of radio waves as these waves can travel through the vacuum

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