NCERT Solutions for Class 8 Science Chapter 13 Sound

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Written by Team Trustudies
Updated at 2021-02-11


NCERT solutions for class 8 Science Chapter 13 Sound Exercise

Q.1 Choose the correct answer.
Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids and gases



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

(d) solids, liquids and gases

Q.2 Voice of which of the following is likely to have a minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

(c) A man

Q.3 In the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.
(a) Sound cannot travel in vacuum. (T/F)
(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
(f) Unwanted or unpleasant sound is termed as music. (T/F)
(g) Noise pollution may cause partial hearing impairment. (T/F)



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

(a) True (b) False (c) False (d) True (e) False (f) False (g) True

Q.4 Fill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called __________.
(b) Loudness is determined by the __________ of vibration.
(c) The unit of frequency is __________
(d) Unwanted sound is called __________ .
(e) The shrillness of a sound is determined by the __________ of vibration.



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

(a) Time taken by an object to complete one oscillation is called __time period__.
(b) Loudness is determined by __the amplitude__ of vibration.
(c) The unit of frequency is __Hertz__.
(d) Unwanted sound is called __Noise__.
(e) The shrillness of a sound is determined by the __frequency__ of vibration

Q.5 A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

Time period = time ÷ number of oscillation
= 4second÷40 = 1/10 second = 0.1 second
Frequency = Total number of oscillations/Total time taken
=40/4 =10 Hz

Q.6The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

Number of vibrations per second = 500
Time period = time ÷ number of vibration
= 1/500 = 0.002 second

Q.7 Identify the part which vibrates to produce sound in the following instruments.
1. Dholak
2. Sitar
3. Flute



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

1. Dholak - Stretched membrane
2. Sitar - string of sitar
3. Flute - air column

Q.8 What is the difference between noise and music? Can music become noise sometimes?



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

The unpleasant sound is called noise. whereareas the pleasant sound is called music. noise can produce so many health hazards whereareas music brings about shooting effect.
Yes music can become a noise sometime when the musical instruments produce very high volume

Q.9 List sources of noise pollution in your surroundings.



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

Noise pollution sources are
(a) Firecrackers and loudspeakers.
(b) mixers at home
(c) Bus and car horns.
(d) High volumes in televisions and transistors.

Q.10 Explain in what way noise pollution is harmful to humans.



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

Noise pollution causes: (a) Lack of sleep
(b) Anxiety
(c) Hypertension.
(d) Hearing loss
(e) Insomnia

Q.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



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

I would suggest my parents to buy the house which is three lanes away from the road side. This would protect us from noise pollution which is maximum at road side building.

Q.12 Sketch larynx and explain its function in your own words.



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

The other name of larynx is voice . It is present at the upper end of the wind pipe. The function of larynx is to be produce sound

Q.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 why?



NCERT Solutions for Class 8 Science Chapter 13 Sound


Answer :

The speed of light is more than that of the speed of sound. Thus, due to more speed of light it reaches us before sound. So, lightning is seen earlier and thunder is heard later.



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