NCERT Solutions for Class 8 Science Chapter 10 - Sound

1. Choose the correct answer.

Sound can travel through

1. gases only

2. solids only

3. liquids only

4. solids, liquids and gases.

Ans: (d) solids, liquids and gases.

Sound can travel in any medium.

2. Which of the following voices is likely to have minimum frequency?

1. Baby girl

2. Baby boy

3. A man

4. A woman

Ans: (c) A man

Frequency of a sound is directly proportional to pitch. Here, the pitch of a man is minimum.

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.

Ans: T

Vacuum is an enclosed place in which there are no molecules or matter. Therefore, sound cannot travel through a vacuum where there is no molecule or atom to induce vibrations.

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

Ans: F

The number of oscillations per second of a vibrating object is known as its frequency. 

c) If the amplitude of vibration is large, sound is feeble.

Ans: F

Sound is feeble for small amplitudes.

d) For human ears, the audible range is \[20\] Hz to \[20,000\] Hz.

Ans: T

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.

Ans: F

The pitch of a sound is proportional to its frequency. As the frequency of vibration increases, the pitch of the sound also increases and vice versa.

f) Unwanted or unpleasant sound is termed as music.

Ans: F

Unwanted or unpleasant sounds are known as noise. 

g) Noise pollution may cause partial hearing impairment.

Ans: T

If one is subjected to loud unpleasant sound continuously for a long time, then it may cause temporary hearing impairment.

4. Fill in the blanks with suitable words.

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

Ans: Time taken by an object to complete one oscillation is called time period.

b) Loudness is determined by the ________ of vibration.

Ans: Loudness is determined by the amplitude of vibration.

c) The unit of frequency is _________.

Ans: The unit of frequency is hertz (Hz).

d) Unwanted sound is called _________.

Ans: Unwanted sound is called noise.

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

Ans: 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.

Ans: Time period is defined as the time required to complete one oscillation.

Frequency is defined as the number of oscillations per unit time.

Here,

Time \[t=4s\]

Number of oscillations \[n=40\]

Frequency \[f=\dfrac{n}{t}\]

Thus, \[f=\dfrac{40}{4}\]

\[\therefore f=10\] Hz

Time period is the inverse of frequency of an object.

Therefore, \[T=\dfrac{1}{f}\]

\[T=\dfrac{1}{10}\]

\[\therefore T=0.1s\]

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 period is the inverse of frequency of an object.

Therefore, \[T=\dfrac{1}{frequency}\]

\[T=\dfrac{1}{500}\]

\[\therefore T=0.002s\]

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

a) Dholak

Ans: Dholak has stretched membranes called heads that vibrate to produce sound.

b) Sitar

Ans: In sitar, the stretched strings are plucked and when they vibrate, they produce sound.

c) Flute

Ans: In flute, the air column inside it vibrates when blown which produces sound.

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

Ans: Noise is an unpleasant sound which is a result of irregular vibrations. Music is a sound which is pleasant to hear. Yes, music can sometimes become noise when it is played at very high volumes on loudspeakers.

9. List sources of noise pollution in your surroundings.

Ans: Following are the major sources of noise pollution:

1. Sounds of vehicle horns.

2. Explosions that include bursting of crackers and explosives.

3. Sounds of machines and loudspeakers.

4. Sounds of television and transistor radio at high volumes.

5. Sounds of kitchen appliances.

10. Explain in what way noise pollution is harmful to humAns:

Ans: Noise pollution is harmful to humans as it may cause many health-related problems; like insomnia, hypertension, headache, stress and may even lead to loss of hearing.

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: I would suggest that the house be three lanes away from the roadside because the house next to the roadside will be more noisy compared to the house three lanes away from the road.

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

Ans: Larynx is a part of the throat. It moves when we swallow something. There are two vocal cords inside the Larynx. The air passes through a small gap between them. The lungs force the air into the space when we speak and this vibrates the vocal cord, resulting in the production of sound. That is why the larynx is also known as a sound box.

Side and Top view of Larynx new

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? 

Ans: 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 because speed of light is greater than the speed of sound and therefore, light travels faster than thunder.

Sound Chapter Class 8 - Quick Overview of Topics Covered 

Important Points for Class 8 Science Chapter 10- Sound

1. Sound is produced by vibrating objects.

2. Vibration is the rapid back-and-forth movement of an object.

3. Sound travels through a medium (solid, liquid, or gas) by compressing and rarefying particles.

4. It cannot travel through a vacuum as no particles transmit the vibrations.

5. Sound travels at different speeds in different media: fastest in solids, slower in liquids, and slowest in gases. 

6. Characteristics of Sound

• Frequency: Number of vibrations per second, measured in Hertz (Hz). Determines the pitch of the sound.

• Amplitude: Height of the sound wave. Determines the loudness of the sound.

• Wavelength: Distance between two consecutive compressions or rarefactions.

• Time Period: The time taken for one complete vibration.

7. Human Ear

• The ear converts sound waves into electrical signals which are interpreted by the brain.

• Parts of the ear: Outer ear (collects sound), Middle ear (amplifies sound), Inner ear (transmits sound to the brain).

8. Noise: Unpleasant, irregular, and random sound waves.

9. Music: Pleasant, regular, and harmonic sound waves.

10. Sound Pollution

• Excessive or unwanted sound can have harmful effects on health and the environment.

• Reducing sound pollution includes using soundproof materials, regulating noise levels, and planting trees.

Benefits of Vedantu’s NCERT Sound Chapter Class 8 PDF

• Class 8 Science Chapter Sound Question Answer clearly explains all the questions discussed in the chapter.

• Sound Chapter Class 8 PDF Questions And Answers covers important concepts related to sound, including its production, propagation, properties, and effects.

• Class 8 Science Chapter Sound delves into the mechanisms of sound production in different musical instruments, human speech, and the functioning of the human ear.

• Sound Chapter Class 8 Question And Answer short question answers assist students in completing their last-minute revisions efficiently and effectively.

• Sound Class 8 incorporates practice questions and exercises that allow students to test their understanding of sound concepts. This practice reinforces learning and prepares students for exams.

• By referring to NCERT Solutions of Sound Chapter Class 8, students can effectively prepare for exams as the solutions cover all the topics and questions likely to be asked in assessments.

Important Study Materials For Class 8 Science Ch 10

For more insights, students can also download additional study materials provided by Vedantu for Chapter 10, Sound Class 8-

Conclusion

Vedantu’s NCERT Solutions for Class 8 Science Ch 10, Sound is essential for understanding the fundamental concepts of sound, such as its production, propagation, and properties. These solutions simplify complex topics, making it easier for students to grasp key ideas. Focusing on understanding how sound travels through different mediums and the characteristics of sound waves is crucial. The previous year’s question paper featured 7-8 questions from this chapter, emphasising its importance in exams. By studying these solutions, students can effectively prepare, ensuring they have a strong grasp of the material and are ready to excel in their exams.  

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