NCERT Class VIII Science Solutions: Chapter 13-Sound Part 3

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Question 8:

What is the difference between noise and music? Can music become noise sometimes?

Answer:

Music is a sound which produces a pleasing sensation while noise is an unwanted and unpleasant sound. Music is produced by nature, musical instruments etc. Noise is produced by horns of vehicles, by machines etc. Music can become noise when we play it at very high volume or too many music are being played at the same time with unpleasant loudness.

Question 9:

List sources of noise pollution in your surroundings.

Answer:

Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers etc. Sources in the home may lead to noise pollution. Television and transistor radio at high volumes, some kitchen appliances, desert coolers, air conditioners, all contribute to noise pollution.

Question 10:

Explain in what way noise pollution is harmful to humans.

Answer:

Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution.

A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

Question 11:

Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.

Answer:

Closer to roadside, larger the noise pollution. So, I would suggest a house which is three lanes away from the roadside because the pollution level (both air and noise pollution) is somewhat less there.

Question 12:

Sketch larynx and explain its function in your own words.

Answer:

In humans, the sound is produced by the voice box or the larynx. Two vocal cords, are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. When the lungs force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords can make the cords tight or loose. When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose and thick.

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Sketch Larynx

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Question 13:

Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen earlier and thunder is heard later. Can you explain?

Answer:

Speed of sound is and speed of light is Light travels much faster than sound that is why lightning is seen earlier and thunder is heard.