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NCERT Solutions, , , , Class-VIII (CHAPTER-13), SOUND, , Answers, , . (d) air, liquid and solids, . (a) Baby girl., », (b), ©), (d), (e), (, , (8) T, Fill in the blanks with suitable words., , 7m an ma, , (a) Time taken by an object to complete one oscillation is called time period., (b) Loudness is determined by the amplitude., (c) The unit of frequency is hertz., , (d) Unwanted sound is called noise., , , , (e) Shrillness of a sound is determined by the pitch of vibration., , . No. of oscillations = 40., , Time- taken = 4 sec., Frequency = no. of oscillation/ time-taken, = 40/4 = 10 Hz., No- of vibration in 1 second = 500,, Therefore, frequency= 500Hz., Time-period = 1/ frequency, = 1/500 = 0.002 second., . (a) Dholak- Stretched membrane., (b) Sitar- Stretched string, , (c) Flute- Air column.

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NCERT Solutions, , , , 10., , 11., , 12., , 13., , 8. The unpleasant sound is called noise. Whereas pleasant sound is called music. Noise, can produce so many health hazards, whereas noise music brings about soothing, effect., , Yes, music can become a noise sometimes when the musical instruments produce, very high volume sounds., , The sources of noise pollution are:, , (i) The sound produced by buses and trucks., , (ii) The sound produced at the construction site., , (iii) The sound produced by playing of T.V., radio and loudspeaker., , (iv) Bursting of crackers, and sound of big machines in the factories., , The noise pollution may cause many health related problems. Lacks of sleep,, hypertension, anxiety etc. are some of the problems that may caused due to noise, pollution. Moreover, a person who is exposed to a loud sound continuously may get, temporary or permanent deafness., , I would suggest my parents to buy the house which is three lanes away from the, roadside. This would protect us from noise pollution which is maximum at roadside, building., , The other name of larynx is voice box. It is present at the upper end of the windpipe., The function of larynx is to produce sound., , The light travels at the speed of 3,00,000 km/s which is very large in comparison to, the speed of sound which travels at the rate of 330 m/s in air. That is why lightening, , is seen earlier and thunder is heard later.