NCERT Class VIII Science Solutions: Chapter 13-Sound Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 23:

An alarm bell is kept inside a vessel as shown in Fig person standing close to it can distinctly hear the sound of alarm. Now if the air inside the vessel is removed completely how will the loudness of alarm get affected for the same person?

As Showing in Fig is a an Alarm Bell is Kept Inside a Vessel


The loudness of the sound will decrease as the air is removed slowly from the plastic bottle. If the air in the plastic bottle is removed completely, there is vacuum in the bottle. The sound cannot travel through vacuum and we cannot hear the sound of the alarm clock at all.

Question 24:

The town hall building is situated close to BooJho՚s house. There is a clock on the top of the town building which rings the bell every hour. Boojho has noticed that the sound of the clock appears to be much clearer at night. Explain hall.


The noise level is quite low at night. Therefore the sound of the clock appears much clearer at night than in the day.

Question 25:

Suggest three measures to limit noise pollution in your locality.


  1. Trees must be planted along the roads and around the buildings.
  2. Use of horns should be minimised.
  3. Silencers must be installed in transport vehicles and industrial machines.
Measurement of Noise