Question

(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 moon?

Answer 1

(a) If the air is gradually pumped out of the glass vessel, no sound of the electric bell can be heard because vacuum is created in the vessel and there are no air molecules to carry sound vibrations. Hence, sound waves require material medium for its propagation.

(b) Sound cannot be heard on the surface of moon because there is no air on the moon to carry the sound waves. Hence, sound waves cannot be propagated in vacuum.
Astronauts talk to one another on the surface of moon through wireless sets that uses radio waves. This is because radio waves can travel through vacuum, whereas sound waves cannot travel through vacuum as they require material medium for their propagation.