NCERT Solutions for Class 8 Science Chapter 13-Sound, contains solutions to various questions in Exercise for Chapter 13. At the end of the Solutions, all the keywords and Notes which are important to understand Science Chapter 13-Sound, have been explained in a simple and easy to understand manner. NCERT Solutions for Class 8 help to check the concept you have learned from detailed classroom sessions and the application of your knowledge.
| Category | NCERT Solutions for Class 8 |
| Subject | Science |
| Chapter | Chapter 13 – Sound |
Download NCERT Solutions for Class 8 Science Chapter 13 Sound
NCERT Solutions for Class 8 Science Chapter 13-Sound– NCERT Exercises
Question 1
Choose the correct answer :
Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids and gases.
Answer 1.
(d) solids, liquids and gases.
Question 2
Which of the following voices is likely to have minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
Answer 2.
(c) A man
Question 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.
(b) The number of oscillations per second of a vibrating object is called its time period.
(c) If the amplitude of vibration is large, sound is feeble.
(d) For human ears, the audible range is 20 Hz to 20,000 Hz.
(e) The lower the frequency of vibration, the higher is the pitch.
(f) Unwanted or unpleasant sound is termed as music.
(g) Noise pollution may cause partial hearing impairment.
Answer 3.
(a) T
(b) F
(c) F
(d) T
(e) F
(f) F
(g) T
Question 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.
Answer 4.
(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 (Hz).
(d) Unwanted sound is called Noise.
(e) Shrillness of a sound is determined by the frequency of vibration.
Question 5
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer 5.
Total number of oscillations = 40
Total time taken to complete 40 oscillations = 4 seconds
Time period is the time taken to complete one oscillation
Therefore, Time period = 4/40 = 0.1 seconds
Frequency is defined as the number of oscillations in one second or 1/Time period
Therefore, Frequency = 1/Time period = 1/0.1 = 10 hertz.
Question 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?
Answer 6.
The time period of the vibration is equal to the inverse of its frequency.
Time period = 1/ frequency = 1/ 500 = 0.002 seconds.
Question 7
Identify the part which vibrates to produce sound in the following instruments:
(a) Dholak (b) Sitar (c) Flute
Answer 7.
(a)The vibrating part in a dholak is a stretched membrane.
(b)The vibrating part in a Sitar is its stretched strings.
(c)The vibrating part in a flute is the air column inside it.
Question 8
What is the difference between noise and music? Can music become noise sometimes?
Answer 8.
Noise is defined as the unwanted, unpleasant sound which is judged to be disruptive to hearing.
Music, on the other hand, is defined as the pleasant sound produced which is pleasant to the ears, such as the sound produced by the musical instruments.
Yes, music can sometime become sound for some people. It is a subjective issue. For example, old people tend to regard the modern-day music as noise whereas teenagers seem to enjoy it. So, for old people it is noise whereas for teenagers it is music.
Question 9
List sources of noise pollution in your surroundings.
Answer 9.
Sources of noise pollution in our surroundings are-
- Televisions at high volumes
- Loudspeakers
- Burning of crackers
- Horns of trucks, cars and motorcycles etc.
- Sound of machines operating in factories
- Loud music in parties and weddings
Question 10
Explain in what way noise pollution is harmful to humans.
Answer 10.
There are many harmful effects of noise pollution. They include-
(a)Noise pollution can cause temporary or permanent damage to our ears
(b)It can increase the risk of high blood pressure
(c)It can result in insomnia or sleep deprivation
(d)It can cause headaches, stress and severe hypertension
Question 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.
Answer 11.
It is suggested to buy a house that is three lanes away from the roadside because buying a house on the roadside would cause the people living there to suffer from a lot of noise pollution especially from the transport like honking of cars, buses and trucks. That would lead to various other problems including health problems like stress, anxiety, tension and other disturbances in daily life.
Question 12
Sketch larynx and explain its function in your own words.
Answer 12.
The larynx or the voice box is responsible for phonation and for maintaining the pitch, loudness and amplitude of vibration produced by us. It is also known as the voice-box and allows us to produce sound.
Question 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?
Answer 13.
Lightning is seen earlier and thunder is heard later because the speed of light is very much faster as compared to the speed of sound. The speed of light is 299,792,458 m/sec whereas the speed of sound is only about 330m/sec in air. As a result of this difference in speed, the sound produced by thunder takes some time to reach our ears whereas light reaches almost immediately to our eyes.
Topics Covered in Chapter 13 Sound Class 8 Science :-
- Sound is Produced by a Vibrating Body
- Sound Produced by Humans
- Sound Needs a Medium for Propagation
- We hear Sound through Our Ears
- Amplitude, Time Period And Frequency Of A Vibration
- Audible and Inaudible Sounds
- Noise and Music
Important Terms Relevant to understand NCERT Solutions for Class 8 Science Chapter 13 – Sound
Vibrations: Vibrations are the mechanical phenomena which causes the atoms to oscillate about an equilibrium point.
Larynx: Larynx is also known as the voice-box. It houses the vocal chords and is responsible for maintain pitch, loudness and phonation.
Loudness: Loudness is an attribute of sound which determines the magnitude of the auditory sensation heard by our ears.
Frequency of oscillations: The number of oscillations made by a vibrating body in one second is known as its frequency. Its unit is Hertz(Hz).
Amplitude: The maximum displacement of a vibrating body from its mean or equilibrium position is known as its amplitude.
Pitch: Pitch is an attribute of sound which is governed by the rate of vibrations producing the sound. It is also known as shrillness.
Noise:Noise is an unwanted, loud and unpleasant sound produced by a source that is judged to be disruptive to hearing.
Music: Music is the sound produced by an abject which is pleasing to the ear such as the sound produced by the musical instruments.
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