Subject Experts Solutions for Chapter: Sound, Exercise 3: TOUGH NUT

Sheena recently went to a planetarium where she learnt about the universe and the celestial objects. Next, she enthusiastically narrated her experience to Reena. While doing so she also told her that recently an explosion took place on the moon and it was heard on the earth.

Do you think this is possible?

Why do we get to see the lightning first and hear the thunder later?

When an aeroplane flies close over our houses, the glass windows start shaking. Why?

Two friends Rajesh and Rakesh were walking on the road on a moonlit night. Rajesh: I like to stare at the moon. It looks so peaceful. Rakesh: Yes, the moon is a quiet, comfortable place. I like the fact that there is no traffic on the moon and therefore, no sound pollution. Rajesh: Even the presence of traffic could not have caused noise pollution on the moon. Rakesh: Yes, that is true. The moon is smaller than the Earth and has much less gravity. So sound waves cannot travel on the moon and cause noise pollution. Rajesh: No, that is wrong! We know that sound waves cannot travel in vacuum and always need a medium. Since there is no air on the moon, sound cannot propagate on the moon.

Who is right—Rakesh or Rajesh?

Two friends Rajesh and Rakesh were walking on the road on a moonlit night. Rajesh: I like to stare at the moon. It looks so peaceful. Rakesh: Yes, the moon is a quiet, comfortable place. I like the fact that there is no traffic on the moon and therefore, no sound pollution. Rajesh: Even the presence of traffic could not have caused noise pollution on the moon. Rakesh: Yes, that is true. The moon is smaller than the Earth and has much less gravity. So sound waves cannot travel on the moon and cause noise pollution. Rajesh: No, that is wrong! We know that sound waves cannot travel in vacuum and always need a medium. Since there is no air on the moon, sound cannot propagate on the moon.

List three types of pollution not mentioned above.

Two friends Rajesh and Rakesh were walking on the road on a moonlit night. Rajesh: I like to stare at the moon. It looks so peaceful. Rakesh: Yes, the moon is a quiet, comfortable place. I like the fact that there is no traffic on the moon and therefore, no sound pollution. Rajesh: Even the presence of traffic could not have caused noise pollution on the moon. Rakesh: Yes, that is true. The moon is smaller than the Earth and has much less gravity. So sound waves cannot travel on the moon and cause noise pollution. Rajesh: No, that is wrong! We know that sound waves cannot travel in vacuum and always need a medium. Since there is no air on the moon, sound cannot propagate on the moon.

State three measures which we can take to reduce noise pollution. 

Rahul's exams will start from next Sunday. He has to prepare for his exams but is afraid that a local festival is approaching on the same dates when some inconsiderate people in his locality will worship God with loudspeakers on full volume, at times, even till late night. Last year, Rahul suffered from headache and nausea due to the blaring sound of loudspeakers and he is afraid that the same practice will be repeated this time. Rahul's friend Jason advises him to go and talk to the elders in their society. Rahul, with much fear and nervousness, approaches the elders and shares his problem with them. The elders hold a meeting separately and decide that due to the forthcoming exams of students in the community, loudspeakers will not be used at the time of the local festival.

Can noise pollution affect an individual's health?

Rahul's exams will start from next Sunday. He has to prepare for his exams but is afraid that a local festival is approaching on the same dates when some inconsiderate people in his locality will worship God with loudspeakers on full volume, at times, even till late night. Last year, Rahul suffered from headache and nausea due to the blaring sound of loudspeakers, and he is afraid that the same practice will be repeated this time. Rahul's friend Jason advises him to go and talk to the elders in their society. Rahul, with much fear and nervousness, approaches the elders and shares his problem with them. The elders hold a meeting separately and decide that due to the forthcoming exams of students in the community, loudspeakers will not be used at the time of the local festival.

What are the things that we can learn from this passage?