NCERT Solutions for Class 8 Science Chapter 13 - 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.

NCERT Solutions for Class 8 Science Chapter 13 – Free PDF Download

This is the right place you have reached to look for the NCERT solutions for Science Class 8 Chapter 13. Get the answer prepared by the experts in PDF format from the official website of Vedantu. Fulfil your requirements about the question and get the right NCERT Solutions for Class 8 Science Chapter 13.

Chapter 13 – Sound

Importance of Sound

Sound Is important because it can lead us to the ways that the visual can't. It is also potentially important because it can help us to determine what we see. Sound can also allow us to know about a character, place, and time. It helps us to communicate with one another. Sound can help us recognize someone's presence by just hearing the footsteps or hearing the voice. Chapter Sound Class 8 will help the students to learn more about how the sound plays. An important role in our lives.

Source of Sound

There are two types of sources of Sound, which are natural and human-made. Animals. Bing flowing streams are examples of natural sources of Sound. Sound of the road vehicles, trains, explosions. Factories are considered as examples of manmade sources of Sound. The vibration of a body can also produce Sound. The sound chapter Class 8 describes the sources of Sound in a straightforward way.

Audible and Inaudible Sound

A body's vibration can produce Sound unless the sound frequencies are less than 20Hz or more than 20,000. The human ear is not able to discover sound frequencies, which are less than 20 Hz. It sounds that we cannot see are known as inaudible Sound. Which sound frequencies are between 20 Hz and 20000 Hz that the human ear can detect are known as audible Sound. Learn more about the audible and inaudible Sound from the experts' solution in the CH 13 Science Class 8 answers.

Noise Pollution

Noise pollution is usually defined as regular exposure to elevated sound levels, which will cause adverse effects in humans or other living organisms. Consistent with the planet Health Organization, sound levels but 70 dB aren't damaging to living organisms, no matter how long or consistent the exposure is.

Unwanted sound (noise) can damage physiological health. Sound pollution is related to several health conditions, including cardiovascular disorders, hypertension, high-stress levels, tinnitus, deafness, sleep disturbances, and various other harmful and disturbing effects. Noise pollution, also widely known as environmental noise or noise pollution, is the propagation of noise with ranging impacts on human or animal life activity, most of them harmful to a degree.

The source of outside noise worldwide is especially caused by machines, transport, and propagation systems. Poor urban planning may produce noise disintegration or pollution; side-by-side industrial and residential buildings may result in sound pollution within the residential areas. Some of the most sources of noise in residential areas like loud music, transportation (traffic, rail, airplanes, etc.), lawn care maintenance, construction, electrical generators, explosions, and other people. In animals, noise can maximize the danger of death by changing predator or prey detection and avoidance, interfere with reproduction and navigation, and donate to permanent deafness. A substantial amount of the noise that humans produce occurs within the ocean.

In NCERT Science Class 8 Chapter 13, the experts have elaborated about the noise pollution in a very uncomplicated way, which will help the students understand how excessive and unwanted Sound can be the cause of the noise pollution. Mainly the human-made voices are the reason for the noise pollution. Noise pollution is mostly caused by bursting the crackers, loudspeakers, or The Sound of the vehicles.

Music & Noise

NCERT solutions Class 8 Science Chapter 13 will provide A detailed description of music and noise.

Noise is Sound with endless structure. The music consists of sounds with fundamental overtones. Noise consists of sounds with frequencies that range continuously in value from as low as you'll hear to as high as you'll listen to - not necessarily at equal intensity, however. Musical Sound is one that is pleasing to the ear. The Sound produced by a harmonium is musical. The string of a sitar also gives out a musical sound. But, if a musical sound becomes too loud, it would not be melodious anymore.

Exercise 13.8 total solutions: 13 Questions (4 short questions, 9 long questions).

Key Points to Remember

The following are the key points that are discussed in the chapter, understanding these points will help students to develop a deeper understanding. 

• Sound is produced by a vibrating body.

• The to-and-fro or back-and-forth movement of an object is known as vibration. 

• To travel, sound needs a medium. In simpler words, the sound can not travel in a vacuum.

• Waves that move through a solid object are known as mechanical waves.

• The direction of motion of the medium's particles and wave propagation are used to classify waves.

• Transverse and longitudinal waves are the two types of waves.

• Amplitude refers to the size of the disturbance in the medium on each side of the mean value.

• Frequency is defined as the number of oscillations per second.

• The ear is responsible for hearing.

• The auditory canal is a tube through which sound travels. Vibrations are sent to the inner ear, which then sends signals to the brain via the auditory nerve.

Key Features of NCERT Solutions for Class 8 Science Chapter 13

NCERT solutions Class 8 Science Chapter 13 provided by Vedantu offers proper guidance for the students. The Sound Class 8 NCERT solutions provide questions and answers from the NCERT books in a very detailed way. It's the only intention is to make the study easier to understand for students.

• Students can revise the Class 8 Science chapter Sound solutions before sitting in the exams.

• The Class 8 Science Chapter 13 solution provides a deep understanding of the students and gives them more insights into the chapter.

• The NCERT Solutions for Class 8 Science CH 13 are prepared by our well-experienced experts, helping you easily clear all your doubts.

• The NCERT Solutions for the Class 8 Science chapter sound allows you to understand how to answer the questions perfectly.

• The NCERT solution of Class 8 Science Chapter 13 will help you clear your fundamentals and the concept of the chapter.