# NCERT Solutions for Class 8 Science Chapter 13 Sound

## NCERT Solutions Class 8 Science Chapter 13 â€“ Free PDF Download

*According to the CBSE Syllabus 2023-24, this chapter has been renumbered as Chapter 9.

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, which are executed by a team of subject-matter experts with thorough knowledge of the subject. Referring to and solving these solutions will be one of the best ways to crack examinations and score outstanding marks. These solutions are easily accessible and completely reliable, with step-by-step instructions to understand solutions in the most simplified manner. Practising solutions is one of the most appropriate strategies to outperform in examinations.

The solutions are solved skillfully using easily comprehensible language for the Class 8 students. This helps them understand the concepts, thus promoting active and efficient learning. The solutions provided are reviewed by the expert team and carefully designed to score maximum marks on the lines of the CBSE exam.Â The NCERT Solutions assist in getting familiarised with the concepts given in the textbook.Â

## NCERT Solutions for Class 8 Science Chapter 13 Sound

### Access Answers to Science NCERT Class 8 Chapter 13 Sound

Exercise Questions

Sound can travel through

(a) gases only

(b) solids only

(c) liquids only

(d) solids, liquids and gases

Soln:

The answer is (d) solids, liquids and gases

Explanation:

For the sound to travel, it requires a medium. Solids, liquids and gases provide a medium through which sound can travel.

2. Voice of which of the following is likely to have a minimum frequency?

(a) Baby girl

(b) Baby boy

(c) A man

(d) A woman

Soln:

The answer is (c) A man

Explanation:

When compared to the voices of a baby boy, baby girl, andÂ woman, the voice of a man has a lower pitch. As the pitch of a man is low, which is proportional to the frequency of a sound, the manâ€™s voice is of minimum frequency as compared with others.

3. In the following statements, tick â€˜Tâ€™ against those which are true and â€˜Fâ€™ against those which are false.

(a) Sound cannot travel in a 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 the vibration is large, the 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 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)

Soln:

a) True â€“ A medium is required for sound to travel

b) False â€“ A vibrating object whose number of oscillations per second is known as its frequency. The time taken to complete one oscillation is called a time period.

c) False â€“ The square of the amplitude of vibration is proportional to the loudness of sound. Sound is loud when the amplitude of vibration is large. For a feeble sound, the amplitude is small.

d) True â€“ Sounds of all frequencies are not audible to human ears. The range of frequencies which are audible to human ears is between 20 Hz and 20,000 Hz. Sounds outside these frequencies are not audible to human ears.

e) False â€“ Higher the frequency, the higher the pitch of the sound, as the pitch is proportional to its frequency. For high-pitched sounds, its vibrating frequency is high, and for low-pitched sounds, its vibrating frequency is small.

f) False â€“ Music is a melodious and pleasing sound which is pleasant to hear. Noises are unpleasant sounds.

g) True â€“ Noises are unwanted and unpleasant sounds which cause temporary hearing impairment when heard continuously for a long period of time.

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) The shrillness of a sound is determined by the __________ of vibration.

Soln:

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

Soln:

The number of oscillations per second of the vibrating body is known as the frequency of oscillation.

Frequency =Â Total number of oscillations

Total time taken

=Â 50/5

= 10 Hz

The time period is the time taken to complete one oscillation. It is also the inverse of frequency.

Time period =Â  1/Oscillating frequency

=Â 1/10

= 0.1 s

âˆ´ frequency = 10 Hz

Time period = 0.1 s

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?

Soln:

The time period is defined as the time taken to complete one oscillation. It is also the inverse of frequency.

Time period =Â  1

Oscillation frequency

Oscillation frequency = 500 Hz

The time period of the vibration = 1/500 = 0.002 s

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

(a) Dholak

(b) Sitar

(c) Flute

Soln:

a) Dholak â€“ It consists of a head which is a stretched membrane. Vibrations are set into these stretched strings. When the head is beaten gently, these vibrations produce sound, and thus Dholak produces sound.

b) Sitar â€“ It is a musical instrument. Stretched strings are part of it. Vibrations are produced when the string is plucked when played. These vibrations produce sound, and thus sitar produces sound.

c) Flute â€“ Itâ€™s an instrument which has holes in it. It is a hollow pipe. The air inside the pipe is set into vibration when air is blown over its mouth, and this produces a pleasant sound.

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

Soln:

Music is a sound which is pleasant to hear. Sounds from flutes, pianos and violins are pleasant to hear.

Noises are sounds which are unpleasant to hear.

Sounds which are unpleasant to hear are:

(a) Sounds from bus horns and truck horns.

(b) Electrical generator sounds.

(c) Gunshot sounds.

(d) Jackhammer sounds

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

9. List sources of noise pollution in your surroundings.

Soln:

Noise pollution sources in ou surroundings are listed below:

(a) Bus and car horns

(b) Firecrackers and loudspeakers

(c) High volumes in televisions and transistors

(d) Mixers at home

e) Sirens from factories

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

Soln:

A number of health issues are associated with noise pollution. They are as follows:

(a) Stress

(c) Hearing loss

(d) Insomnia

(e) Hypertension

Soln:

It is better to buy the 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 the noise decreases. So itâ€™s better to buy the house which is three lanes away from the roadside.

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

Soln:

When we swallow something, the larynx moves.Â  There are two vocal cords inside the larynx. The air passes through a small gap which is present in between them. The lungs force the air into the gap when we speak, 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?

Soln:

The speed of light is more than the speed of sound. Thus, lightning is seen first, which is accompanied by thunder later.

### About NCERT Solutions Class 8 Science Chapter 13 Sound

The NCERT solutions cover the answers to the questions provided in the CBSE Class 8 Science Textbook along with extra questions, exemplary problems, important questions from previous question papers, worksheets and tips to write the exam.

Sound is a crucial Chapter in CBSE Class 8, and students must prepare this chapter to score well in their exams. NCERT Solutions for Class 8 Science Sound is one of the best tools to prepare for the Class 8 Science annual exams. The solutions for this chapter are also available in PDF format for the students to access and download for free.

### Subtopics of NCERT Solutions for Class 8 Science Chapter 13 Sound

1. Sound is Produced by a Vibrating Body
2. Sound Produced by Humans
3. Sound Needs a Medium of Propagation
4. We Hear Sound through Our Ears
5. Amplitude, Time Period and Frequency of a Vibration
6. Audible and Inaudible Sounds
7. Noise and Music
8. Noise Pollution

The Central Board of Secondary Education is one of the popular educational boards in India. CBSE follow the NCERT curriculum to conduct its examinations for Class 10 and Class 12, respectively. Class 8 is one of the crucial stages in studentsâ€™ academic life as it lays the foundation for the concepts taught in Class 10.

Sound is produced by vibrating objects. We hear a variety of sounds in our surroundings. Some key points to remember from the chapter are given below.

• In human beings, the vibration of the vocal cords produces sound.
• The eardrum senses the vibrations of sound, it sends the signals to the brain. This process is called hearing.
• The frequency is expressed in Hertz (Hz)
• Unpleasant sounds are called noise.
• Attempts should be made to minimise noise pollution
• Plantation on the roadside and elsewhere can reduce noise pollution.
• Sound travels through a medium (gas, liquid or solid). It cannot travel in a vacuum.
• Excessive or unwanted sounds lead to noise pollution. Noise pollution may pose health problems for human beings.
• The higher the frequency of vibration, the higher the pitch, and the shriller the sound.
Attempts should be made to minimise noise pollution.

Sound is an important topic for the Class 8 students as it comprises very basic concepts. Students should understand this topic thoroughly in order to avoid any difficulty in understanding related topics in their higher classes.

## Frequently Asked Questions on NCERT Solutions for Class 8 Science Chapter 13

Q1

### What are the topics and subtopics present in Chapter 13 of NCERT Solutions for Class 8 Science?

The topics and subtopics present in Chapter 13 of NCERT Solutions for Class 8 Science are as follows:
Sound is Produced by a Vibrating Body
Sound Produced by Humans
Sound Needs a Medium of Propagation
We Hear Sound through Our Ears
Amplitude, Time Period and Frequency of a Vibration
Audible and Inaudible Sounds
Noise and Music
Noise Pollution
Q2

### How can I score full marks in Chapter 13 of NCERT Solutions for Class 8 Science?

The NCERT Solutions for Class 8 Science Chapter 13 is prepared by highly experienced faculty after conducting vast research on each concept. While solving the textbook questions, students can refer to these solutions to get an overall idea about the topics covered in this chapter. The solutions can be accessed in both online and offline modes as per the needs of students. The PDF format of solutions is available on BYJUâ€™S, which can be downloaded and used by the students to get their doubts cleared instantly.
Q3

### Explain the concept of audible and inaudible sounds covered in Chapter 13 of NCERT Solutions for Class 8 Science.

The human ear can easily detect frequencies between 20 Hz and 20 kHz. Hence, sound waves with frequency ranging from 20 Hz to 20 kHz is known as audible sound. Human ears cannot detect sound frequencies of less than 20 vibrations per second, i.e. 20 Hz. So any sound below this frequency will be an inaudible sound for humans. In the high-frequency range, the human ear cannot detect frequencies above 20000 vibrations per second (20 kHz), and the amplitude of the wave would be dependent on the loudness of the sound. So the frequencies below 20 Hz and above 20 kHz come under the category of inaudible frequencies. The stepwise explanations in simple language boost the confidence of students to appear for the exam without fear.