NCERT Class 8 Science Chapter 13 Sound

NCERT Class 8 Science Chapter 13 Sound Solutions to each chapter is provided in the list so that you can easily browse through different chapters NCERT Class 8 Science Chapter 13 Sound and select need one. NCERT Class 8 Science Chapter 13 Sound Question Answers Download PDF. NCERT Class 8 Science Solutions.

NCERT Class 8 Science Chapter 13 Sound

Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 8 Science Solutions are part of All Subject Solutions. Here we have given NCERT Class 8 Science Chapter 13 Sound and Textbook for All Chapters, You can practice these here.

Sound

Chapter: 13

NCERT TEXT BOOK EXERCISES

Q. 1. Choose the correct answer: 

Sound can travel through:

(a) gasses only.

(b) solids only.

(c) liquids only.

(d) solids, liquids and gasses

Ans. (d) solids, liquids and gasses.

Q. 2. Voice of which of the following is likely to have minimum frequency:

(a) Baby girl.

(b) Baby boy.

(c) A man.

(d) A woman.

Ans. (a) Baby girl.

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)

Ans. True. 

(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)

Ans. False. 

(c) If the amplitude of vibration is large, sound is feeble. (T/F)

Ans. False. 

(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)

Ans. True. 

(e) The lower the frequency of vibration, the higher is the pitch. (T/F)

Ans. False. 

(f) Unwanted or unpleasant sound is termed as music. (T/F)

Ans. True. 

(g) Noise pollution may cause partial hearing impairment. (T/F)

Ans. True.

Q. 4 Fill in the blanks with suitable words:

(a) Time taken by an object to complete one oscillation is called _________.

Ans. time period.

(b) Loudness is determined by the _________ of vibration.

Ans. amplitude.

(c) The unit of frequency is __________.

Ans. hertz.

(d) Unwanted sound is called __________.

Ans. noise.

(e) Shrillness of a sound is determined by the __________ of vibration.

Ans. frequency.

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

Ans. Time taken by pendulum to complete 40 oscillation = 4 seconds.

Time taken by pendulum to complete

1 oscillation = 4/40 = 1/10 = 0.1 sec.

Time period of pendulum = 0.1 sec.

Frequency of pendulum

= 40 oscillation/4 time = 10 Hz.

Q. 6. The 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?

Ans. Time taken to complete 500 vibrations = 1 second

Time taken to complete 1 vibration = 1/500

= 0.002. Time period of vibration = 0.002 second.

Q. 7. Identify the part which vibrates to produce sound in the following instruments:

(a) Dholak.

Ans. Stretched membrane.

(b) Sitar.

Ans. Strings.

(c) Flute.

Ans. Air column.

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

Ans.

Music	Noise
1. Sound which is pleasant to the ears is called music.	1. Sound which is unpleasant to the ears is called noise.
2. Vibrations are regular and periodic in music.	2. Vibrations are irregular and non-periodic in noise.

Music become noise sometimes when it crosses the bearable range of sound for our, ears.

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

Ans. There are various sources which cause sound pollution in our surroundings like: Honking of horns, loud sounds of machines in factories, loud musics in parties and marriages, loud sound of T.V. or radio, loud sounds of domestic electronic appliances like mixer grinder etc., are some sources of noise in our environment.

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

Ans. (i) Noise pollution can cause temporary or permanent deafening.

(ii) It can cause many health related problems like high blood pressure.

(iii) It can cause mental illness due to lack of sleep.

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 to buy? Explain your answer.

Ans. I would suggest my parents to buy a house which is three lanes away from the roadside. It is because the house situated on the roadside will have the following disadvantages in comparison to the house three lanes away from roadside:

(i) Lot of noise due to passing of vehicles.

(ii) Smoke and dust produced due to traffic on road.

(iii) Sound of pressure horns at the time of traffic jams or during peak hours of the traffic.

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

Ans. 

The human beings produce sound by using the larynx. Larynx is situated in our throat at the top of wind-pipe. The larynx contains two ligaments known as vocal cords. Sound is produced by the vibrations of vocal cords.

Q. 13. 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.

Ans. Lightening and thundering take place simultaneously but we see light earlier than thunder because light travels faster than sound, so it reaches us before the sound does.