Question

(a) What is sound? What type of waves are sound wave in air?
(b) Describe an experiment to show that sound cannot pass through vacuum.

Answer 1

(a) Sound is a form of energy that makes us to hear. Sound waves are longitudinal waves in air.

(b) Sound cannot travel through vacuum. This can be shown by the following experiment:
(i) A ringing electric bell is placed inside an airtight bell jar containing air. We can hear the sound of the ringing bell clearly. Thus, when air is present as medium in the bell jar, sound can travel through it and reach our ears.
(ii) The bell jar containing a ringing bell is placed over the plate of a vacuum pump. Air is gradually suctioned from the bell jar by switching on the vacuum pump. As large amount of air is suctioned from the bell jar, the sound of the ringing bell weakens. Ultimately, when all the air is suctioned from the bell jar, there is no sound heard. Thus, when vacuum is created in the bell jar, the sound of the ringing bell placed inside it cannot be heard. This shows that sound cannot travel through vacuum.