Class 8 NCERT Science Chap 13 Solution

CHAPTER 13 

SOUND

Here is the answer of chapter 13 SOUND of NCERT science of class 8.The complete solution of CHAPTER 13  SOUND is given here which is prepared subject expert. Some important extra questions and important points about Chapter 13 are also given.

Textbook questions:-

Ques1.  Choose the correct answer. 

(1)  Sound can travel through

a)Gases only

b)Solids only

c)Liquids only

d)Solids, liquids and gases 

Ans 1.Solids, liquids and gases. 

Ques 2) Voice of when of the following is likely           to have minimum frequency? 

a)Baby girl 

b)Baby boy 

c)A man 

d)A woman 

Ans.2 Baby girl

Ques 3.   In the following statements, tick 'T' against those which are true and 'F' against those which are false.

a)Sound cannot travel in vaccum. (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 20Hz to 20,000Hz.(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)

Answers .

a)T

b)F

c)F

d)T

e)F

f)F

g)T

Ques 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)Shrillness of a sound is determined by the -----------of vibration. 

Answers .

a)Time period 

b)Amplitude 

c)Hertz

d)Noise

e)Pitch

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

Ans 5. Number of oscillations = 40

Time taken = 4seconds 

Frequency = number of oscillations /time

                  = 40/4

                  = 10Hz

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

Ans 6. Number of vibration in 1 second = 500

Therefore, frequency = 500Hz

Time period = 1/frequency

                    =1/500

                    =0.002second

Ques7 Identify the part which vibrates to produce sound in the following instruments.

a)Dholak

b)Sitar

c)Flute

Answers.

a)Stretched membrane 

b)Stretched string

c)Air column

Ques8 What is the difference between noise and music? Can music become noise sometimes? 

Ans 8. The unpleasant sound is called noise. Whereas pleasant sound is called music. Noise can produce so much health hazards, whereas music brings about soothing effect. 

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

Ans 9. The sources of noise pollution are automobiles, loud speakers, aeroplanes, machine etc. 

Ques 10 .Explain in what way noise pollution is harmful to human.

Ans 10.  Noise pollution causes:-

1)Temporary or permanent deafness 

2)Blood pressure 

3)Lack of concentration 

Ques 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. 

Ans 11.  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. 

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

Ans 12.  The other name of larynx is voice is box. It is present at the upper end of the windpipe. The function of larynx is to produce sound. 

Ques13  Lightening and thunder take place in the sky at the same time and at the same distance from us. Lightening is seen earlier and thunder is heard later. Can you explain why?

Ans 13.The speed of light is much greater than the speed of sound. Hence, lightening is seen earlier and thunder is heard later, even through both are produced at the same time and same place. 

This is the complete solution of CHAPTER 13 SOUND. This is according to latest syllabus of CBSE 2020-21.

Here's some important points about the  CHAPTER 13 SOUND of class 8 Science NCERT.

IMPORTANT POINTS:-

1)Frequency :- The number of oscillation in seconds is called frequency. The SI unit of frequency is Hertz. 

2)Amplitude:-  The maximum displacement of a vibrating body from its mean position on either side. 

3)Time period:- The time taken by a vibrating body to complete an oscillation  is called time period. It is denoted by T.

4)vibration:- Vibration is defined as to and fromotion of the body in the same path about its mean position. 

5)Pitch:- Characterstics of sound that depends upon the frequency of vibration. 

6)Noise:- Sound produces by irregular vibration which is unpleasant to ears. 

7)Decible:-  A unit to measure the loudness of the sound.

8)Music:- Sound produced by regular vibrations which is pleasant to ears in music.

These are some important points about the Chapter 13 SOUND of Class 8 Science.

Here's some extra questions are given according to CHAPTER 13 SOUND of class 8 Science NCERT.

Extra Question/Answers

Ques 1.What happens when you ring the bell of your bicycle?

Ans 1. When we ring the bell of bicycle it starts vibrating and produces sound.

Ques 2. Which part of our throat produces sound?

Ans 2 .The sound of our voice is produced by the vibration of two vocal cords in our throat causes by air  coming from lungs.

Ques 3. How sound is produced in a radio or television?

Ans 3.The sound in a radio or television is produced by the vibration of tjin diaphragm of a speaker.

Ques 4.Which part of a bee and mosquito produced buzzing sound?

Ans 4.The buzzing sound of a bee and mosquito is produced by the vibration of their wings.

Ques 5. What is the range of audible sound vibrations for normal human ears?

Ans 5. The range of audible sound vibration for normal human ear is 20Hz to 20,000Hz.

Ques 6.What is the range of ultrasonic vibrations?

Ans 6.The range of ultrasonic vibration is more than 20,000Hertz.

Ques 7.Name the characterstics which help us distinguish between Men and woman voice?

Ans 7.Pitch.

Ques 8.Why should we not put any pointed or hard thing in our ear?

Ans 8.Beacause it tears the eardrum.The tearing of ear drum can make a  person deaf.

Ques 9.Suggest four ways of minimizing noise?

Ans 9.a)The machines which produced   minimum noise should be used.  

b)The factories should not be in town sheep  area.

c) Fire crackers should be banned.

d)Domestic appliances should be lubricated.

Ques 10. What is noise pollution ?State two ways in which noise produced in home?

Ans 10 . The persistence of unwanted sound or loud noise in the environment which sometimes had harmful effects  on human health is termed as Noise pollution.

The two ways in which noise is produced in home are:-

1)Radio and television when put on high volumes.

2)Air coolers, air conditions etc cause noise pollution.

These are some extra Questions of Chapter 13 SOUND of class 8 Science NCERT.

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