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NCERT Solutions for Class 8 Science Chapter 13: Sound

Chapter 13 Sound
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NCERT Solutions for Class 8 Science chapter 13 Sound renders students with accurate solutions to all the exercises and in-text questions provided in the NCERT Class 8 textbook that aligns with the CBSE board. Here, students are provided with the ultimate study material, the NCERT Class 8 solutions that are executed by a team of subject matter experts with thorough knowledge of the subject. Referring and solving these solutions should be one of the best ways to crack examinations and score outstanding marks.

NCERT Solutions for Class 8 Science Chapter 13 by Swiflearn are by far the best and most reliable NCERT Solutions that you can find on the internet. These NCERT Solutions for Class 8 Science Chapter 13 are designed as per the CBSE Class 8 Science Syllabus. These NCERT Solutions will surely make your learning convenient & fun. Students can also Download FREE PDF of NCERT Solutions Class 8 Chapter

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NCERT Solutions for Class 8 Science Chapter 13: Sound

 

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

 

Solution:
Option (d) is the correct answer because sound requires a medium for its propagation.

 

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

 

Solution:
Option (c) is the correct answer because a man’s voice has lower pitch. And pitch is directly proportional to frequency.

 

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)

 

Solution:
(a) Sound cannot travel in vacuum. (T)
(b) The number of oscillations per second of a vibrating object is called its time period. (F)
(c) If the amplitude of vibration is large, sound is feeble. (F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T)
(e) The lower the frequency of vibration, the higher is the pitch. (F)
(f) Unwanted or unpleasant sound is termed as music. (F)
(g) Noise pollution may cause partial hearing impairment. (T)

 

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.

 

Solution:
(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) Shrillness of a sound is determined by the frequency of vibration.

 

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

 

Solution: Refer pdf.

 

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?

 

Solution:Refer pdf.

7. Identify the part which vibrates to produce sound in the following
instruments.
(a) Dholak
(b) Sitar
(c) Flute

 

Solution:
a) Dholak– The vibrating part is a stretched membrane.
b) Sitar – The stretched strings vibrate and produce the sound.
c) Flute – The vibrating part is the air column.

 

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

 

Solution:
Music           
Music is the sound which is pleasant
to the ears.                                                                                                              Sounds from musical instruments such
as flute, piano, etc. are examples of
music.

Noise
Noise is the sound which is unpleasant to
the ears.
Sounds from gunshots, bursting of
firecrackers, loudspeakers, etc. are
examples of noise.

Yes, sometimes when the music is played at high volumes, it becomes noise.

 

9. List sources of noise pollution in your surroundings.

 

Solution:
The various sources of noise pollution in our surroundings are:
a. Sound from the vehicles
b. Sound from the bursting of crackers
c. Sound from loudspeakers, TV, etc.
d. Sound of sirens from factories

 

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

 

Solution:
Noise pollution can cause a number of health problems like:
(a) Stress
(b) Headache
(c) Hearing loss
(d) Insomnia
(e) Hypertension

 

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.

 

Solution:
It is always better to buy a house which is three lanes away from the roadside as there will be less noise as compared to the one on the main road. The noises can be caused by vehicles. As the distance between the source and the listener increases, the intensity of noise decreases.

 

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

 

Solution:
Larynx is known as the voice box. There are two vocal cords inside the larynx. As air passes through a small gap present between the two vocal cords, the lungs force the air into the gap and this vibrates the vocal cord, due to which sound is produced.

 

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?

 

Solution:
The speed of the light is more than the speed of sound. This is the reason why lightning is seen first.

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