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Sound CBSE Class 8 Science Revision Notes Chapter 13

What is sound.

A sound is a form of energy that is produced when air molecules vibrate in a particular pattern called waves. Hence, the sound is a wave.

Vibration can be described as a back and forth motion of an object.

Depending upon the vibrations, a sound is produced. Sound cannot be produced without any vibration.

Figure 1 Production of Sound through Vibrations

Figure 2 Different instruments produce different sounds

How do humans produce sound?

Human beings have a voice box or larynx which is present in their throat on the upper side of the windpipe.

The larynx has two vocal cords which have a narrow slit between them so that air can pass through it.

As the lungs throw the air out of the windpipe, it passes through the slit and hence allows the production of sound as the vocal cords start vibrating.

The vocal cord muscles also play a role in the production of sound.

Their thickness and tightness describe the quality or type of the voice a person has.

The vocal cords in males are of length 20 mm and females have 15mm long vocal cords. Children, on the other hand, have very short length vocal cords. Hence, the voices, their quality and their type are always different in women, men and children.

Figure 3 Larynx or Voice box

Propagation of sound through a medium

Sound always requires a medium to travel from the source of its production to the receiver end. Different mediums of propagation of sound are air, liquid and solids.

Sound cannot travel through a vacuum as it lacks any medium of transmission.

Figure 4 Sound Waves

How sound travels in a medium?

Sound needs some vibration of molecules to travel.

Solids, liquids and gases all have molecules present in them which allow the propagation of sound.

These molecules or particles in solids, liquids and gases are packed in varied ways.

Solids have tightly packed particles in them and hence they allow fast propagation of sound through them as the vibrations can be carried easily from one particle to another.

Liquids have slightly loosely packed particles and hence it takes a little time for sound to travel in water or through a liquid.

Gases have completely loosely packed particles and hence sound takes the most time in travelling through the air.

How do we hear?

We know that sounds are produced as waves in the air or any other medium.

As these sound waves travel to our ears they convert them into electrical signals or messages that our brain can understand.

Our ears have a special structure that allows this function.

There are three major parts of the human ear:

Figure 5 The Human Ear

The outer ear (Pinna): It catches the sound waves and forwards them to the next part of the ear, that is, the middle ear.

The middle ear : It converts the sound waves into vibrations that then travel to the inner ear. It can do this with the help of the eardrum. The eardrum is a thin rubber-like sheet present in the Middle ear. As the sound waves reach the eardrum, it vibrates and these vibrations propagate to the inner ear.

The inner ear (cochlea): It receives the vibrations sent by the eardrum. It contains a liquid substance and the vibrations that enter the inner ear moves through this liquid. There are tiny hairs present inside the inner ear that turn these vibrations into signals for the brain and pass them to the brain through the hearing nerve. As the brain receives the signal it interprets the sound. However, this whole process is so quick that we cannot notice it.

Frequency, Time Period and Amplitude of a Sound

Figure 6 Displacement of Particles by Production of Sound and Representation of A Sound Wave

The loudness of a sound

The loudness of a sound depends upon the amplitude of the sound.

The higher the amplitude, the higher is the displacement of the particles and the higher is the loudness of the sound.

The loudness of the sound is directly proportional to the square of its amplitude.

The SI unit for measuring the loudness of a sound in decibels (dB).

Pitch of the sound

Every person has a different sound quality.

Also, every musical instrument vibrates to produce a different kind of sound. This quality of sound is characterized by its Different quality of sounds may have same pitch and loudness.

The pitch of a sound depends upon the frequency of the sound wave.

The pitch would be higher if the frequency of the sound is high.

Different organisms and objects have different type of sound because of varied pitch:

Figure 12 Loudness and Pitch of a Sound

How Loudness and Pitch are different from each other?

Audible and inaudible sounds.

Sounds that can be heard by human ears are called audible sounds . The range of audible sounds is from 20 Hz to 20 KHz.

Sounds that cannot be heard by human ears are called inaudible sound . Any sounds having a frequency less than 20 Hz or greater than 20 KHz are categorized as inaudible sounds.

Figure 15 Loudness of Sound from various Sources

The inaudible sounds can be divided into two categories as infrasound and ultrasound.

Figure 16 Infrasound and Ultrasound

Noise and Music

Noise can be regarded as an unpleasant sound. Noise consists of sound waves of varied frequencies which have no particular periodic pattern of repetition. Therefore, noise is regarded as a mixture of sound waves with irregular frequencies.

Music , on the other hand, is a pleasant sound that has a clear pitch. Musical sound can be created by arranging and combining different sounds in a particular order. The frequencies of a musical sound are harmonious in nature.

Figure 17 Noise And Music

Noise pollution

Noise pollution can be defined as the presence of undesirable and unpleasant sounds in the earth's environment.

Human beings can bear sounds ranging up to 85 decibels only. Above that, any noise can damage our hearing power.

Generally, any sound that has a frequency of more than 30 dB is considered noise.

The unwanted noise causes an adverse effect on the health of the organisms present on the earth.

According to the World Health Organization, the maximum sound limit that is ideal for cities is 45 dB only.

However, it has been found that the sound range in many big cities of the world lies up to 90 dB.

Hence noise pollution is common in many cities today and even rural areas to a great extent.

Figure 18 Noise Pollution

Causes of noise pollution

Transport noise: The sound of the traffic on roads, railways and aircraft leads to noise pollution. As the number of vehicles such as cars, motorcycles, buses and trucks is increasing in the cities, especially the Metropolitans, noise pollution is extremely high there.

Industrial noise: Industries, factories and other commercial businesses cause high-intensity sounds that pollute the environment.

Neighbourhood noise : The noise from the radios, televisions, air conditioners, coolers, kitchen applications and other electrical appliances used in houses lead to noise. Not only this, commercialization around the residential areas often leads to unwanted sounds due to small-scale industries such as printing, car repairing etc.

Construction noise: Construction of houses, industries and various architectures also lead to sound pollution.

Political activities: Noise pollution is also created due to the rallies and demonstrations conducted by various political parties in cities and rural areas.

Bursting of crackers and fireworks: People burst crackers on several occasions such as festivals and ceremonies that lead to sound pollution in the neighbourhoods.

Natural sounds: The environment of the earth also sometimes leads to unpleasant sounds due to lightning, thunderstorms, earthquakes, volcanic eruptions, sounds of various animals etc.

Figure 19 The Noise Thermometer

Effects of Noise Pollution

Excessive noise in the surroundings can lead to serious health problems such as hypertension, lack of sleep or insomnia, anxiety, lack of memory, stress, irritation and even nervous breakdown.

It can lead to temporary or permanent hearing loss in human beings as well as animals.

Excessive noise leads to increased blood pressure. It increases cholesterol levels in the blood and therefore increases the chances of cardiovascular diseases in a person.

If sound intensity is more than 180 dB it can lead to the death of a person.

Noise pollution also leads to a decrease in the production of digestive juices by our body.

It can affect animals as well and can lead to their death and loss of habitats. Excessive noise decreases a person's ability to concentrate especially on children and they are unable to concentrate well on their studies due to neighbourhood noises.

Unwanted sounds in the environment can hinder the animals from finding their prey or their direction of motion.

Prevention of Noise Pollution

Factories and other industries should be set up at a distance from residential areas.

Silencing devices should be incorporated into heavy vehicles such as aircraft, industrial equipment, machinery and other home appliances.

We should always play television, radio and other music systems at a low sound so that it does not harm the neighbourhood.

Use of horns should be minimized especially near public places such as hospitals, religious places and schools.

Soundproofing systems should be installed in industries, party halls and other buildings that produce a high amount of unwanted sounds.

Trees should be planted in huge numbers as they can absorb unwanted noise from the environment.

People who work in noisy conditions such as industries and mines should be provided earplugs to protect their ears.

People should be made aware of noise pollution its adverse effects so that they can take an active involvement in preventing it.

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NCERT Solutions for Class 8 Science Chapter 13 Sound

Chapter 13 Sound Class 8 Science NCERT Solutions

Class 8 science chapter 12 friction ncert questions and answers - topics, chapter 13 sound ncert solutions for class 8 science  - notes, chapter 13 sound class 8 science questions and answers - mcq questions with answers, contact form.

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Chapter 13 Class 8 - Sound

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Get NCERT Solutions, Extra Questions, Worksheets, and Notes of Chapter 13 Class 8 Sound. Teachoo also provides solutions of all Maths and Science  NCERT Questions with explanation of Concepts.

In this chapter, we will study

What is Sound ?

How is sound produced ?

Different Musical Instruments and how sound is produced in them

What is Medium of Sound? In which medium does sound travel?

Amplitude, Frequency and Time Period of Sound

Difference between Frequency and Amplitude

How is sound produced by Humans

How do we hear sounds ?

What do you mean by Noise and Music?  

What is the difference between Noise and Music

What is Noise Pollution ?

What are the c auses and effects of Noise Pollution

How to reduce Noise Pollution ?

What is Hearing Impairment?

What are Audible and Inaudible Sounds

What are Ultrasonic Sounds ?

What are the different methods of producing sound ?

When we hear a sound, does any part of our body vibrate ? Name the part.

Does any part of the body vibrate when we speak ? Name the part.

Why is the voice of men, women and children different ?

In which medium sound travels more faster - Water, Glass, Air, Vacuum. Why?

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• Important Questions for CBSE Class 8 Science Chapter 13 - Sound

CBSE Class 8 Science Chapter-13 Important Questions - Free PDF Download

The CBSE important questions of Chapter Sound Class 8 have been set, keeping in mind the board’s syllabus and question pattern. Professionals set Class 8 Science Sound important questions after thorough and careful evaluation of the chapter. There are MCQ-type questions along with concise type, short type, and long type. NCERT Class 8 Science Chapter 13 essential questions are also included here making sure that our students get the best possible preparation before examinations.

The crucial questions of chapter Sound Class 8 help the students clearly understand the lesson, focus on the important questions, gather knowledge, and boost their confidence before appearing in the final examinations. Vedantu is a platform that provides free CBSE Solutions (NCERT). You can also download Class 8 Maths NCERT Solutions and Class 8 Science NCERT Solutions to help you to revise complete syllabus and score more marks in your examinations.

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Study Important Questions for Class 8 Science Chapter 13 – Sound

Very Short Answer Questions:

1. Which one the following acts as a medium for propagation of sound.

B. Gas 

C. Liquid 

D. All of These

Ans: D. All of these act as a medium for propagation of sound.

2. The range of audible sound for a human being is ____________. 

A. 20 Hz to 20,000 Hz 

B. 20 Hz to 10,000 Hz 

C. 10 Hz to 10,000 Hz

D. 20 Hz to 40,000 Hz

Ans: A. 20 Hz to 20,000 Hz is the range of audible sound for a human being.

3. The loudness of sound depends upon ______________. 

A. Amplitude 

B. Frequency

C. Time Period

Ans :A. amplitude is the property on which loudness of the sound depends upon.

4. Which one of the following will have long vocal cords? 

A. Women 

C. Children 

D. None of the above

Ans: B. Men have long vocal cords

5. Shrillness of a sound is determined by___________________ of vibration.

B. Frequency 

C. Time Period 

Ans : B. Frequency of vibration determines the shrillness of a sound.

6. Which one of the following instruments produces sound through vibrations? 

A. Ghatam 

C. Flute 

Ans: D. Sitar is the instrument which produces sound through vibration.

7. To and fro motion of an object is called _____________. 

Ans : Vibration is the to and fro motion of an object.

8. Define frequency? 

Ans : Frequency is the number of oscillations made per second. 

9. What is the unit of frequency? 

Ans: Hertz is a unit of measurement for frequency. The sign for it is Hz.

10. _______ and _______ are two important properties of any sound. 

Ans: Amplitude and frequency are two important properties of any sound.

11. In humans, sound is produced by the ______________. 

Ans : in humans, sound is produced by the Voice box or larynx 

12. For the human ear, the range of audible frequencies is roughly from ______ to ______ Hz. 

Ans: 20 to 20,000 is the range of audible sound for the human ear.

13 Define noise. 

Ans : Noise is the name given to unpleasant sounds.

14. Give two examples of noise pollution.

Ans: During an event, the use of crackers and loudspeakers .

15. What would be the sound produced in a bus station or railway station called as? 

Ans: Unpleasant noise will be produced in both locations, which is known as noise.

16. Sound cannot travel through a _____________. 

Ans : Sound cannot travel through a vacuum.

Short Answers Questions:

17. Briefly describe the loudness of sound. 

Ans: The Square of the amplitude of the vibration producing the sound determines the loudness of the sound. For example, doubling the amplitude increases the loudness by a factor of four. The decibel is a measurement of how loud something is (dB).

18. Classify the following into music and noise. Desert coolers, sound produced by harmonium, string of sitar, television and transistor radio at high volumes

19.  Describe oscillatory motion. 

Ans: Oscillating is the process of swinging back and forth in a continuous motion, and oscillating motion is the result of that process.

20.  Label the parts of the human ear in the below given picture.

Ans : A. Inner ear, B. Eardrum

21.  Correct the following statements. 

a. Noise is one which is pleasing to the ear. 

Ans : Musical sound is one which is pleasing to the ear

22. Sounds of frequencies more than 20 Hz but less than 20,000 Hz cannot be detected by the human ear. 

Ans: Sounds of frequencies more than 20 Hz but less than 20,000 Hz can be detected by the human ear.

23.  Explain with an activity that sound travels in liquids. 

Ans: Fill a bucket with water and, using one hand, shake a bell under the water, making sure the bell does not touch the bucket's body. Now carefully place your ear on the water's surface; you will hear the ringing bell, proving that sound can travel through water .

24. Give an example to show that the frequency determines the shrillness or pitch of a sound. 

Ans : A low-frequency vibration is produced by a drum. As a result, it makes a low-pitched sound. A whistle, on the other hand, has a high frequency and hence generates a higher pitch sound.

25. It is said that “The loudness of sound depends on its amplitude”. What happens to the sound when the amplitude of vibration is large and vice versa?

Ans : Because the loudness of sound is determined by its amplitude, so  the sound produced is loud when the amplitude of vibration is significant. The sound generated is weak when the amplitude is tiny.

26. Sound plays an important role in our life. Why? 

Ans : Sound is crucial because it enables us to communicate with one another.

27. Identify the type of frequency in the below given pictures.

 a. High frequency  

 b. low Frequency

Long Answers Questions:

28. Explain how sound is produced in human beings. 

Ans: The voice box or the larynx in humans produces the sound. The larynx is located near the top of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that a thin slit for air passage is left between them. The vocal cords vibrate when the lungs force air through the slit, producing sound. The muscles that link to the voice cords can tighten or loosen them. The sort or quality of voice produced when the vocal cords are tight and thin differs from that produced when they are loose and thick.

29. Demonstrate an activity to show that sound needs a medium for propagation 

Ans: Take a tumbler, either metal or glass. Make sure it's completely dry. Put a cell phone in there. Request that a friend call this cell phone from another cell phone. Pay close attention to the ring. Now, wrap your hands over the tumbler's rim. Place your mouth in the space created by your hands. Tell your friend to ring the phone once more. While sucking air from the tumbler, listen to the ring. Keep an eye on the tumbler and take it out of your mouth. It's probable that the decreased volume of air in the tumbler contributed to the ring's decreased volume. There would be no sound if the tumbler is completely devoid of air. This demonstrates that sound requires a medium in order to travel.

30. List the harmful effect of Noise pollution

Ans : Excessive noise in the environment can lead to a variety of health issues. 

a. Lack of sleep, 

b. Hypertension (high blood pressure), 

c. Anxiety, 

d. A person who is continuously exposed to a loud sound may suffer from temporary or permanent hearing loss.

31. How can we control Noise pollution?

Ans : We must control the causes of noise pollution in order to reduce noise pollution. 

a. Aircraft engines, transport vehicles, industrial machines, and household appliances must all have noise-cancelling devices fitted. 

b. All loud operations must take place outside of any residential areas. Industries that produce noise should be located distant from such regions.

c. Automobile horns should be used sparingly. Low-volume television and music systems are recommended.

d. Trees should be planted along highways and around buildings to reduce the amount of noise that reaches households, hence lowering the negative impacts of noise pollution.

CBSE Important Questions Class 8 Science Chapter 13

Solved questions from sound chapter class 8 questions.

1. Explain how sound is produced in human beings.

Answer: The voice box or the larynx produces the sound in human beings. The larynx is at the upper end of the windpipe. A narrow slit is left between the two vocal cords because they are stretched over the larynx. This helps in the passage of air. The lungs force air through the slit, producing sound as the voice box vibrates. Muscles that are attached to the vocal cords make the cords tight or loose. When the vocal cords are flexible and thick, the type or quality of voice is different from that of when they are tight and thin.

2. Explain an activity to show that sound needs a medium to propagate.

Answer: Take a metal or glass tumbler, making sure that it is dry. Place a cell phone in it and ask a friend to ring that phone with another cell phone. Now carefully listen to the ring. Now surround the rim of the tumbler with your hands. After this, put your mouth on the opening between your hands. Now ask your friend to call the cell phone again. Listen to the ring while sucking air from the tumbler. Observe and remove the tumbler from your mouth. It is possible that the decreasing amount of air in the tumbler had something to do with the decreasing loudness of the ring. If the air is sucked completely from the tumbler, you will not hear any sound. This is how we can prove that sound needs a medium to propagate.

3. How can we control noise pollution?

Answer: We can control noise pollution by controlling the sources of noise. Following are some of the ways we can control noise pollution:

1. Silencing devices should be used in aircraft engines, industrial machines, transport vehicles, and home appliances.

2. All noisy activities should be conducted far away from residential areas. Industries should be set up away from residential areas because of how much noise they produce.

3. The use of TV, music systems, and automobile horns should be minimised. 

4. More trees should be planted to curb the harmful effects of noise pollution.

4. Describe the oscillatory motion.

Answer: Oscillation is the process of swinging to and fro in an uninterrupted manner and oscillation motion is the movement created by this process.

5. What are some of the harmful effects of noise pollution?

Answer: Excessive noise leads to many health problems in humans. Some of them    are:

Lack of sleep

Hypertension, i.e. high blood pressure

If a person is exposed to excessive noise for an extended period of time, they might temporarily or permanently face hearing loss.

Why are Important Questions for Class 8 Science Chapter 13 - Sound Necessary?

Vedantu’s Important Questions for Class  8 Science Chapter 13 - “Sound” are the finest material to understand and practice the topics in the best way.

The material carries all the information in detail and pointwise.

All the cases of the material are solved in the simplest way which explains the term clearly.

Vedantu’s Important Questions for Class  8 Science Chapter 13 - Sound provides all the main topics so that the student can focus on it and prepare for the exam. 

V encourage all Class 8 students to take advantage of the resources offered by Vedantu to learn and excel in Chapter 13 - Sound. By using the resources provided by Vedantu, students can gain a strong understanding of the concepts covered in the chapter and improve their chances of success in Science and other subjects.

In addition to the resources mentioned above, Vedantu also offers personalized online tuition classes, live interactive learning, and doubt-solving sessions. These resources can be especially helpful for students who are struggling with particular concepts or who need extra help preparing for their exams.

FAQs on Important Questions for CBSE Class 8 Science Chapter 13 - Sound

1. Will the Sound Chapter Class 8 Questions Help me?

Class 8 Science ch 13 important questions are currently available on our website in PDF format with solution keys. These important questions of chapter sound Class 8 have been compiled by our professionals keeping in mind the question pattern as given by CBSE and the questions appearing in previous years. The questions compiled are that they would help students better prepare for the upcoming examinations, grow their knowledge, strengthen their base, and boost their confidence. NCERT Chapter 8 Science essential questions are also included here to ensure students get the best preparation possible before their examinations.

2. What are Some of the Class 8 Chapter 13 Important Questions?

The Class 8 Chapter 13 crucial questions are now available on our website with a detailed analysis of the questions and a solution key. Chapter 13, Sound, is a very vital chapter that appears every year in examinations. We have compiled some MCQs, very short questions, short questions, and long questions to aid the students. This helps the students strengthen their knowledge about the Sound chapter. Some of the most common questions we see appearing each year are:

Define frequency. What is the unit of frequency?

Describe the loudness of sound.

Describe oscillatory motion.

Explain how sound is produced in human beings.

What are the harmful effects of sound pollution?

How can we control noise pollution?

3. What is an oscillatory motion?

Periodic or oscillatory motion is defined as a motion that repeats itself. Due to a regulating force or torque, an item in such motion oscillates around an equilibrium position. Regardless of whatever way the body is pushed, such force or torque tends to restore (return) the system to its equilibrium position. Two conditions must exist for vibration to take place and they are toughness and momentum. The complete explanation along with important questions of Class 8 Science Chapter 13 is easily available on Vedantu app and website.

4. Explain larynx function.

The larynx, or voice box, produces sound in humans. The larynx is located near the top of the windpipe. Because the vocal cords are stretched over the larynx, a tiny slit is left between them. The larynx moves when we swallow something.Two vocal cords can be found in the larynx. Between them, there is a little space through which the air travels. When we talk, our lungs drive air into the gap, which causes the vocal cord to vibrate, producing sound.

5. What is noise pollution?

Any unpleasant or undesired noise that interacts with or affects humans or wildlife is referred to as noise pollution. Noise pollution, despite the fact that it is always there, receives less attention than water and air quality concerns since it cannot be seen, tasted, or smelled. It is the presence of loud, unwelcome, and irritating sounds in our surroundings. By blowing their horns and making noise with their engines, motor vehicles on the road pollute the environment. For revision notes and NCERT solutions for Chapter 13 Class 8 Science, visit Vedantu.

6. How is noise pollution caused?

Outside noise is mostly generated by machines, transportation, and propagation systems all around the world. Poor urban design can lead to noise disintegration or pollution. For example, sound pollution in residential neighbourhoods can be caused by industrial and residential buildings being built next to one other. Loud music, transportation (traffic, rail, aircraft, etc. ), lawn care maintenance, building, electrical generators, explosions, and people are some of the most common sources of noise in residential neighbourhoods.

7. What is the difference between music and noise?

Noise is made up of noises with frequencies that vary in value from as low as you can hear to as high as you can hear. But not always in equal strength. The term "musical sound" refers to a sound that is agreeable to the ear. A harmonium's sound is pleasing to the ear. A sitar's string produces a musical sound as well. However, if a melodic sound grows too loud, it ceases to be melodious. To know more, solve the important questions by visiting the page Important questions for Class 8 Science and  download a free PDF of the same.

Chapterwise Important Questions for CBSE Class 8 Science

Cbse study materials.

Sound Class 8 Science Extra Questions and Answers

Sound Class 8 Science Chapter 13 Extra Questions and Answers are provided here. We prepared these extra questions based on the latest NCERT Class 8 Science Book. CBSE Class 8 Science Chapter 13 Sound Extra Questions will help you to properly understand a particular concept of the chapter.

Class 8 Science Chapter 13 Sound Extra Questions

Very short answer type question.

Question 1: Name one animal which can hear ultrasonic sounds.

Answer: Dogs

Question 2: How is sound produced?

Answer: Sound is produced by vibrating objects.

Question 3: How does an object produce sound?

Answer: Sound is produced when an objects vibrates.

Question 4: Name the sound producing organ in humans.

Answer: Voice box (larynx)

Question 5: Name the organs of hearing in our body.

Answer: Our ears are the organs of hearing in our body.

Question 6: Name that part of ear which vibrates when outside sound falls on it.

Answer: Eardrum vibrates when outside sound falls on it.

Question 7: Name the unit used to measure the loudness of sound.

Answer: The loudness is expressed in a unit called decibel (dB).

Question 8: Name the quantity whose unit is ‘hertz’.

Answer: The unit of frequency is called “hertz”.

Question 9: Does any part of the body vibrate when we speak? Name the part.

Answer: Yes, vocal chords vibrate when we speak.

Question 10: On what factor does the pitch of a sound depend?

Answer: The frequency determines the shrillness or pitch of a sound.

Question 11: What is the name of passage in outer ear which carries sound waves to the eardrum?

Answer: The sound is carried through the Ear canal.

Question 12: What is frequency of oscillation?

Answer: The number of oscillations per second is called the frequency of oscillation.

Question 13: What is the audible range of frequencies for human ears?

Answer: For human ear, the range of audible frequencies is roughly from 20 to 20,000 Hz.

Question 14: What is vibration?

Answer: The to and fro or back and forth motion of an object is termed as vibration.

Question 15: How does a sound producing object differ from silent?

Answer: A sound producing object vibrates while a silent does not. We can feel the vibrations by touching them.

Question 16: What brings the sound of a ringing telephone bell to our ears?

Answer: The sound of a ringing telephone bell travel to our ears through the air in the room.

Question 17: What is the length of the vocal cord in men and women?

Answer: The vocal cords in men are about 20mm long. In women these are about 5mm shorter.

Question 18: What does the working of a toy telephone tell us about sound?

Answer: The working of a toy telephone tells us that sound travels through solid substances.

Question 19: Who produces sound of higher pitch: a man or a woman? Why?

Answer: Usually the voice of a woman has a higher frequency and therefore, produces a sound of higher pitch. 

Question 20: Name three characteristics which are used to describe oscillations.

Answer: Frequency, amplitude and frequency are the three characteristics which are used to describe oscillations.

Question 21: What is musical sound? Give example.

Answer: Musical sound is one which is pleasing to the ear. Sound produced by a harmonium is a musical sound.

Question 22: What is noise pollution?

Answer: Presence of excessive or unwanted sounds in the environment is called noise pollution.

Question 23: What is amplitude of oscillation?

Answer: The maximum displacement of a vibrating object from its central position is called the amplitude of oscillation.

Question 24: Why can ultrasound not be heard by humans?

Answer: Ultrasound cannot be heard by humans because the ultrasound equipment works at frequencies higher than 20,000 Hz.

Question 25: What is the relation between ‘time-period’ and ‘frequency’ of an oscillating body?

Answer: Time Period given by the inverse of the frequency. Time Period = 1/frequency

Question 26: Name one solid, one liquid and one gas through which sound can travel.

Answer: Solid: Metal (Iron, Steel, Aluminium), wood, bricks etc. Liquid: Water Gas: Air

Short Answer Type Questions

Question 1: Why a sound cannot be heard on the moon?

Answer: A sound cannot be heard on the moon because on the moon there is no medium such as air though which the vibrations can propagate.

Question 2: Why should we not put a sharp, pointed or hard thing into our ears?

Answer: We must never put a sharp, pointed or hard thing into our ear. It can damage the eardrum. The damaged eardrum can impair hearing.

Question 3: How is sound produced in mridangam?

Answer: When we strike the membrane of a mridangam, the sound that we hear is not only that of the membrane but of the whole body of the instrument.

Question 4: What differences will you hear in a sound if there is an increase in (i) amplitude, and (ii) frequency?

Answer: (i) The sound will become loud on increasing the amplitude. (ii) The sound will become shrill on increasing the frequency.

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

Answer: Frequency = (Number of Oscillations)/Time = 40/4 = 10 Hz

Time period = 1/(Frequency of Oscillation) = 1/10 = 0.1 sec

Question 6: 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: Speed of the light is more than the speed of sound. Thus, Lightning is seen earlier and thunder is heard later.

Question 7: Whose voice is more shriller: a baby or a woman?

Answer: The voice of a baby has a higher frequency (or higher pitch) than that of a woman due to which the voice of a baby is even more shrill than that of a woman.

Question 8: How does sound of a bird differ from roar of a lion?

Answer: A bird makes a high-pitched sound whereas a lion makes a low-pitched roar. However, the roar of a lion is very loud while the sound of the bird is quite feeble.

Question 9: Which produces sound of a higher pitch: a drum or a whistle? Why?

Answer: A drum vibrates with a low frequency. Therefore, it produces a low-pitched sound. On the other hand, a whistle has a high frequency and therefore, produces a sound of higher pitch.

Question 10: What frequency can dogs hear but not humans?

Answer: Some animals can hear sounds of frequencies higher than 20,000 Hz. Dogs have this ability. The police use high frequency whistles which dogs can hear but humans cannot.

Question 11: Can sound travel through a vacuum? Why or why not?

Answer: Sound cannot travel through a vacuum. A vacuum is an area without any air, like space. So, sound cannot travel through space because there is no matter for the vibrations to work in.

Question 12: How does loudness depend on the amplitude of vibrations?

Answer: Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. For example, if the amplitude becomes twice, the loudness increases by a factor of 4.

Question 13: How is sound produced in Sitar?

Answer: When we pluck the string of an instrument, like the sitar, the sound that we hear is not only that of the string. The whole instrument is forced to vibrate, and it is the sound of the vibration of the instrument that we hear.

Question 14: Why are the voices of men, women and children different?

Answer: The vocal cords in men are about 20mm long. In women these are about 5mm shorter. Children have very short vocal cords. This is the reason why the voices of men, women and children are different.

Question 15: How can you show that a sounding tabla is vibrating?

Answer: If we put some grains on the membrane of sound producing tabla, the grains will start jumping up and down showing that the tabla membrane is vibrating while producing sound.

Question 16: How can we distinguish between a man’s voice and a woman’s voice even without seeing them?

Answer: We can distinguish between a man’s voice and a woman voice even without seeing them. This is because the voice of a woman has a higher frequency and is shriller than that of a man.

Question 17: What can be done along the roads to reduce noise pollution caused by traffic from reaching the residents of the area?

Answer: Trees must be planted along the roads and around buildings to cut down on the sounds reaching the residents, thus reducing the harmful effects of noise pollution.

Question 18: State one observation from everyday life which shows that sound travels slower than light.

Answer: 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. This shows that sound travels slower than light.

Question 19: What are called inaudible sounds?

Answer: The fact is that sounds of frequencies less than about 20 vibrations per second (20 Hz) and higher than about 20,000 vibrations per second (20000 Hz) cannot be detected by the human ear. Such sounds are called inaudible sounds.

Question 20: How is pitch related to frequency?

Answer: The frequency determines the shrillness or pitch of a sound. If the frequency of vibration is higher we say that the sound is shrill and has a higher pitch. If the frequency of vibration is lower, we say that the sound has a lower pitch.

Question 21: 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: Time period = 1/(Frequency of Oscillation) Frequency of oscillations = 500 Hz Time period = 1/500 = .002 s

Question 22: What is the frequency of a vibrating body whose time-period is 0.05 second?

Answer: Time period = 1/(Frequency of Oscillation)

Or, Frequency = 1/ Time period = 1/0.05 second = 20 Hz

Question 23: By how much will the loudness of a sound change when the amplitude of vibrations is: (a) doubled? (b) halved?

Answer: (a) If the amplitude of vibrations is doubled, then the loudness will become four times.

(b) If the amplitude of vibrations is halved, then the loudness will become one-fourth.

Question 24: Write the loudness of the following in decibels: Normal breathing, Soft whisper (at 5m), Normal conversation, Busy traffic and Average factory

Answer: Normal breathing – 10 dB Soft whisper (at 5m) – 30 dB Normal conversation – 60 dB Busy traffic – 70 dB Average factory – 80 dB

Question 25: Identify the part which vibrates to produce sound in the following instruments: (a) Dholak (b) Sitar (c) Flute (d) Cymbals (e) Veena (f) Tabla

Answer: Dholak – stretched membrane Sitar – strings Flute – air columns Cymbals – metal plates Veena – strings Tabla – stretched membrane

Long Answer Type Questions

Question 1: 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: I would suggest my parents to buy the house which is three lanes away from the roadside because being away from the road will reduce noise pollution caused by heavy traffic on the road. The intensity of noise decreases with the distance between the source and the listener.

Question 2: Explain in what way noise pollution is harmful to humans.

Answer: Presence of excessive noise in the surroundings may cause many health related problems. Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution. A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

Question 3: What is the frequency of the sound produced when the vocal cords are: (a) tight and thin? (b) loose and thick?

Answer: Muscles attached to the vocal cords can make the cords tight or loose.

(a) When the vocal cords are tight and thin, a sound of high frequency (high pitch sound) is produced.

(b) The frequency produced by tight and thin, a sound of low frequency (low pitch sound) is produced.

Question 4: How do we hear?

Answer: The shape of the outer part of the ear is like a funnel. When sound enters in it, it travels down a canal at the end of which a thin membrane is stretched tightly. It is called the eardrum. The eardrum is like a stretched rubber sheet. Sound vibrations make the eardrum vibrate. The eardrum sends vibrations to the inner ear. From there, the signal goes to the brain. That is how we hear.

Question 5: List sources of noise pollution in your surroundings.

Answer: Some sources of noise pollution are as follows:

• Running of mixer and grinder
• Blowing of horns of motor vehicles
• Bursting of crackers
• Taking off and landing of aeroplanes
• Sounds of loudspeakers
• High volumes in televisions and transistors

Question 6: What is the difference between noise and music? Can music become noise sometimes?

Answer: Noise: The unpleasant sounds around us are called noise.

• Blowing of horns of vehicles

Music: The sounds which are pleasant to hear are called music.

Example: Sounds from musical instruments such as harmonium, sitar, guitar, flute etc. If a musical sound becomes too loud, it would become noise.

Question 7: Sketch larynx and explain its function in your own words. Or Describe how sound is produced by the human voice box (or larynx).

Answer: In humans, the sound is produced by the voice box or the larynx. It is at the upper end of the windpipe. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. When the lungs force air through the slit, the vocal cords vibrate, producing sound.

Question 8: State the various measures which can be taken to control noise pollution in our surroundings.

Answer: Measures to limit noise pollution

• Silencing devices must be installed in air craft engines, transport vehicles, industrial machines and home appliances.
• Use of automobile horns should be minimised.
• The noisy operations must be conducted away from any residential area.
• Noise producing industries should be set up away from such areas.
• TV and music systems should be run at low volumes.

Question 9: How can you show that sound cannot travel through a vacuum?

Answer: Take a metal glass tumbler. Place a cell phone in it. Ask your friend to give a ring on this cell phone from another cell phone. Listen to the ring carefully. Now, surround the rim of the tumbler with your hands. Put your mouth on the opening between your hands. Indicate to your friend to give a ring again. Listen to the ring while sucking air from the tumbler. You will observe that the sound become fainter as you suck. If you had been able to suck all the air in the tumbler, the sound would stop completely. Actually, sound needs a medium to travel. When air has been removed completely from a vessel, it is said that there is vacuum in the vessel. The sound cannot travel through vacuum.

At Study Path, you can also learn more about Class 8 Science Chapter 13 Sound by accessing the free exhaustive list of study materials and resources related to the chapter such as NCERT Solutions, Notes, Important Questions, and MCQ.

NCERT Solutions for Class 8 Science Chapter 10 Sound

• 8th June 2023

NCERT Solutions for Class 8 Science Chapter 10 Sound help students to clear all their doubts. These solutions provide you with the answers to all the questions given in the NCERT textbook. CBSE Class 8 Science Chapter 10 Solutions is prepared by expert teachers as per the latest CBSE syllabus and guidelines.

Solving NCERT Solutions will help you to understand the concepts related to Sound NCERT Solutions for Class 8 Science Chapter 10 contains an in-depth explanation of each question of NCERT Science textbook. These solutions cover important concepts in different patterns like MCQs and short answer questions, worksheets and more and help you top score good marks in the exam.

Class 8 Science Sound Questions and Answers

Exercise Questions

 Choose the correct answer: 

Question 1:  Sound can travel through  (a) gases only                                            (b) solids only  (c) liquids only                                         (d) solids, liquids and gases.

Answer: (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 

Frequency of a sound is directly proportional to its pitch and inversely proportional to its amplitude. The voice of an adult man is of lower pitch and high amplitude in comparison to the voices of a baby boy, a baby girl and a woman. The voice of a baby girl has highest pitch among this group.

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 – True

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

(c) If the amplitude of vibration is large, sound is feeble – False

(d) For human ears, the audible range is 20 Hz to 20,000 Hz – True

(e) The lower the frequency of vibration, the higher is the pitch – False

(f) Unwanted or unpleasant sound is termed as music – False

(g) Noise pollution may cause partial hearing impairment – True

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: (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.

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

Answer 5: Here no. of oscillation = 40 Time taken = 4 s

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?

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

Answer:   Dholak: Dholak has stretched membranes which vibrate to produce sound.

Sitar: In sitar, the stretched strings, when vibrate, they produce sound.

Flute: Flute is a wind musical instrument which uses air column to produce sound.

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

Answer 8: Music is a sound which produces a pleasing sensation while noise is an unwanted and unpleasant sound. Music is produced by nature, musical instruments etc. Noise is produced by horns of vehicles, by machines etc.

Music can become noise when we play it at very high volume or too many music are being played at the same time with unpleasant loudness.

Question 9:  List sources of noise pollution in your surroundings.

Answer:   Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines, loudspeakers etc. Sources in the home may lead to noise pollution. Television and transistor radio at high volumes, some kitchen appliances, desert coolers, air conditioners, all contribute to noise pollution.

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

Answer:  Lack of sleep, hypertension (high blood pressure), anxiety and many more health disorders may be caused by noise pollution. A person who is exposed to a loud sound continuously may get temporary or even permanent impairment of hearing.

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: Closer to the roadside, larger the noise pollution. So, I would suggest a house which is three lanes away from the roadside because the pollution level (both air and noise pollution) is somewhat less there. 

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

In humans, the sound is produced by the voice box or the larynx. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air. When the lungs force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords can make the cords tight or loose. When the vocal cords are tight and thin, the type or quality of voice is different from that when they are loose and thick.

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: Speed of sound is 330 m/s and speed of light is 300,000,000 m/s. Light travels much faster than sound that is why lightning is seen earlier and thunder is heard. 

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MCQ Questions for Class 8 Science Chapter 13 Sound with Answers

We have compiled the NCERT MCQ Questions for Class 8 Science Chapter 13 Sound with Answers Pdf free download covering the entire syllabus. Practice MCQ Questions for Class 8 Science with Answers on a daily basis and score well in exams. Refer to the Sound Class 8 MCQs Questions with Answers here along with a detailed explanation.

Sound Class 8 MCQs Questions with Answers

Choose the correct option.

Question 1. The voice box is also called as (a) stomach (b) heart (c) larynx (d) mouth

Answer: (c) larynx

Question 2. Sound is a kind of (a) work (b) energy (c) force (d) pressure

Answer: (b) energy

Question 3. The hearing range of human ear is (a) 20 Hz to 20,000 Hz (b) less than 20 Hz (c) more than 20,000 Hz (d) 20 Hz to 25,000 Hz

Answer: (a) 20 Hz to 20,000 Hz

Question 4. Pitch of sound is determined by its (a) frequency (b) speed (c) amplitude (d) loudness

Answer: (a) frequency

Question 5. The frequency of subsonic sound is (a) more than 20 Hz (b) 100 Hz (c) less than 20 Hz (d) more than 20,000 Hz

Answer: (c) less than 20 Hz

Question 6. Cochlea is a part of (a) hearing organ (b) sound producing organ (c) muscular organ (d) air pollution

Answer: (a) hearing organ

Question 7. 1 hertz is equal to (a) 1 vibration per minute (b) 10 vibrations per minute (c) 60 vibrations per minute (d) 600 vibrations per minute

Answer: (c) 60 vibrations per minute

Question 8. Sound cannot travel through (a) air (b) water (c) iron (d) vacuum

Answer: (d) vacuum

Question 9. The sound in the audible range is called (a) ultrasonic sound (b) sonic sound (c) subsonic sound (d) light sound

Answer: (b) sonic sound

Question 10. Speed is (a) \(\frac {Distance travelled}{Time}\) (b) \(\frac {Time}{Distance travelled}\) (c) Distance travelled × Time (d) Time + Distance travelled

Answer: (a) \(\frac {Distance travelled}{Time}\)

Question 11. A pendulum oscillates 20 times in 4 seconds. Find its time period. (a) 0.05 sec. (b) 0.001 sec. (c) 0.2 sec. (d) 0.1 sec.

Answer: (c) 0.2 sec.

Question 12. Loudness of sound is determined by (a) pitch (b) frequency (c) amplitude (d) time period

Answer: (c) amplitude

Question 13. The number of vibrations made by a vibrating body in one second is (a) frequency (b) noise (c) loudness (d) pitch

Question 14. The maximum displacement of a body from its mean position is called (a) amplitude (b) oscillation (c) periodic motion (d) frequency

Answer: (a) amplitude

Question 15. The velocity of sound at 20°C is approximately (a) 3400 m/sec. (b) 340 m/sec. (c) 430 m/sec. (d) 304 m/sec.

Answer: (b) 340 m/sec.

Question 16. Sound usually travels through which medium to reach our ears? (a) Air (b) Water (c) Wood (d) Asbestos

Answer: (a) Air

Question 17. What is the speed of sound in air? (a) 110 m/s (b) 220 m/s (c) 330 m/s (d) 440 m/s

Answer: (c) 330 m/s

Question 18. What is the length of vocal cords in men? (a) 5 mm (b) 10 mm (c) 15 mm (d) 20 mm

Answer: (d) 20 mm

Question 19. What is the length of vocal cords in women? (a) 5 mm (b) 10 mm (c) 15 mm (d) 20 mm

Answer: (c) 15 mm

Question 20. A vibrating body should oscillate minimum how many times per second to make a sound audible for humans? (a) 10 times (b) 20 times (c) 30 times (d) 40 times

Answer: (b) 20 times

Question 21. The voice box is also called as (a) pharynx (b) throat (c) larynx (d) windpipe

Question 22. Speed of sound in solids is the speed of sound in liquids. (a) same as (b) greater than (c) less than (d) both (b) and (c)

Answer: (b) greater than

Question 23. To and fro or back and forth motion of an object is termed as (a) frequency (b) amplitude (c) vibration (d) time period

Answer: (c) vibration

Question 24. The sound above ……………… is physically painful. (a) 20 dB (b) 40 dB (c) 60 dB (d) 80 dB

Answer: (d) 80 dB

Question 25. If we tighten the strings of an instrument, pitch will be (a) higher (b) lower (c) constant (d) no pitch

Answer: (a) higher

Question 26. In dholak, sound is produced due to (a) stretched membrane (b) stretched strings (c) air column (d) none of these

Answer: (a) stretched membrane

Question 27. The human ear can hear sounds having frequency in range from (a) 200 to 20,000 Hz (b) 20 to 2000 Hz (c) 200 to 2000 Hz (d) 20 to 20,000 Hz

Answer: (d) 20 to 20,000 Hz

Question 28. Sound having frequency below 20 Hz is called (a) infrasound (b) ultrasound (c) megasound (d) microsound

Answer: (a) infrasound

Fill in the Blanks

Question 1. In human beings sound is produced by ………………..

Answer: larynx

Question 2. Sound of frequency lower than 20 Hz is called the ………………..

Answer: infrasonic

Question 3. The ……………….. nerve is also present in the inner ear.

Answer: auditory

Question 4. Sounds which are unpleasant to the ear is called ………………..

Answer: noise

Question 5. Too much noise in our surroundings that causes discomfort is called ………………..

Answer: noise pollution

Question 6. The speed of sound is maximum in ………………..

Answer: solids

Question 7. Sounds of frequencies higher than 20,000 Hz are called the ……………….. sound.

Answer: ultrasonic

Question 8. ……………….. is the time taken by a vibrating body for one complete vibration.

Answer: Time period

Question 9. Above ……………….. the noise becomes physically painful.

Answer: 80 dB

Question 10. Plantation on the roadside can reduce ………………..

Question 11. The hearing range of human ears is ………………..

Answer: 20 Hz to 20,000 Hz

Question 12. The loudness of normal breathing of human is ………………..

Answer: 10 dB

Question 13. Vibration is a repeated ……………….. and ……………….. motion.

Answer: to, fro

Question 14. The loudness of sound is determined by the ……………….. of vibration.

Answer: amplitude

Question 15. The human voice box is called ………………..

Question 16. Sound absorbing materials are required in an auditorium to avoid …………………….

Question 17. The two kinds of sounds we cannot hear are ……………………. and …………………….

Answer: infrasonic and ultrasonic

Question 18. ……………………. of any kind is the principle source of production of sound.

Answer: Vibration

Question 19. …………………… is an instrument used in the laboratory to produce sound of a fixed frequency.

Answer: Tuning fork

Question 20. The vibrations of a simple pendulum are also known as …………………….

Answer: oscillations

Question 21. A soft board will ……………………. most of the sound falling on it.

Answer: absorb

True or False

Question 1. All human beings can hear sounds of frequencies upto 60,000 Hz.

Answer: False

Question 2. The sound in a sitar is produced by plucking its strings.

Answer: True

Question 3. Sound cannot travel through vacuum.

Question 4. Sound does not need a medium for its propagation.

Question 5. The loudness is expressed in a unit called decibel.

Question 6. Loud sounds have high frequencies.

Question 7. Sound travel faster in air, slower in iron.

Question 8. Light travels much faster than sound.

Question 9. Man cannot hear sound of bats.

Question 10. The time taken to complete one oscillation is called frequency.

Question 11. Shriller sound has more frequency.

Question 12. Tabla is a musical instrument.

Question 13. The sound could not travel in solid.

Question 14. The pitch of a sound depends on the frequency of the waves.

Question 15. The pitch of sound produced in a guitar can be altered by reducing the vibrating length of the wire.

Question 16. Voice box is situated at the lower end of the windpipe.

Question 17. Vocal cords are of the same length in both men and women.

Question 18. Sound does not need a medium for propagation.

Question 19. The sound of sitar is produced by plucking its strings.

Question 20. Amplitude measures the pitch of sound.

Question 21. The SI unit of frequency is Hertz.

Match the following

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• Chapter 13 Sound

Lakhmir Singh Solutions for Class 8 Science Chapter 13 Sound

A sound is a form of energy that makes us hear through our ears. There are different varieties of sounds present in our world, and also, we hear many sounds in everyday life. Each sound is special to the object which produces it. The sounds of vehicles, birds, musical instruments, etc., are different, and they produce unique sounds. When an object undergoes vibration, it produces sound. In other words, sound is produced by vibrating objects.

When an object vibrates, the air around it also vibrates and carries that sound to our ears through the vibration of molecules.

The energy required to make an object vibrate and produce sound is produced by some external forces like wind. Some vibrations of sounds can be seen with our eyes, while others can only be felt by touch. Human beings produce sound through a voice box called the larynx, which is located in our throat.

This chapter explains the different sounds produced by different objects, how sounds are produced, their units, the speed of sound and also damages caused by the high volume of sounds and how noise pollution is created.

Lakhmir Singh Science Class 8 Solutions for Chapter 13 Sound

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Access Lakhmir Singh Science Class 8 Solutions for Chapter 13

Very Short Answer Type Questions

Page no: 253

1. How is the sound produced?

Sound is produced by vibrating objects.

2. What should an object do to produce sound?

An object should vibrate to the table to produce sound.

3. How does a sound-making object differ from one that is silent?

A sound-making object vibrates when a silent does not. You can feel the vibrations by touching them.

4. Name the part which vibrates to produce sound in the following:

(a) Its stretched membrane

(b) Its strings.

(c) Its long hollow pipe.

5. What brings the sound of a ringing telephone bell to our ears?

The vibrations of eardrums bring us the sound of a ringing telephone bell.

6. What is the length of vocal cords in a man?

The male vocal cords are between 17mm and 25mm in length.

7. Out of a man and a woman:

(a) who has shorter vocal cords?

(b) who produces a sound of a higher pitch?

(a) A woman has short vocal chords because the length of male vocal chords is between 17mm and 25mm in length and that of woman are between 12.5mm and 17.5mm long

(b) Woman produces a sound of a higher pitch.

8. Give any four sources of sound in a market place.

Solutions :

The four sources of sound in a market place are:

1. Vendors selling eatables or other things.

2. Shopkeepers selling their things.

3. Vehicles in the market area, for example, auto rickshaw, car, etc.

4. Machines or generators noise.

9. Name the sound-producing organ in humans.

Vocal chords are the sound-producing organ in human beings.

10. Which part of our body vibrates when we speak?

Vocal chord vibrates when u speak.

11. What does the working of a toy telephone tell us about sound?

The working of a toy telephone tells us that vibrating objects produce sound and it is carried in all directions in a medium.

12. Name one solid, one liquid and one gas through which sound can travel.

Solid: Metal- Iron, Aluminium etc.

Liquid: Water

13. Which of the following cannot transmit sound?

Water, Vacuum, Aluminium, Oxygen and gas.

A vacuum cannot transmit sound because sound needs a material medium to travel.

14. Is the speed of sound more in water or steel?

The speed of sound is faster in solid as compared to liquid. Thus, the speed of sound is more in steel.

15. Where would sound travel faster-in wood or in the water?

The speed of sound is faster in solid as compared to liquid. Thus, the speed of sound is more in wood.

16. In which medium sound travels faster: air or iron?

The speed of sound is faster in solid as compared to gas. Thus, the speed of sound is more in iron.

17. In which medium sound travels fastest: air, water or steel?

The speed of sound is faster in solid as compared to liquid, and then slowest in gases. Thus, the speed of sound is more in steel, then water and then air.

18. Out of solids, liquids and gases:

(a) in which medium sound travels slowest?

(b) in which medium sound travels fastest?

(a) Sound travels slowest in gas medium

(b) Sound travels fastest in solid medium.

19. What is the speed of sound in air?

The speed of sound in air is 343m/s.

20. Which of the following is the speed of sound in water and which in steel?

(a) 5000 m/s

(b) 1500 m/s

(c) 340 m/s

Solid has a high speed of sound when compared to liquid and gases. The speed of sound is more in steel, then water and then air.

(a) 5000 m/s – Speed of sound in steel.

(b) 1500 m/s – Speed of sound in water.

(c) 340 m/s – Speed of sound in air.

21. Name the organs of hearing in our body.

Our ears are the hearing organ of our body.

22. Name that part of the ear which vibrates when outside sound falls on it.

The eardrum vibrates when outside sound falls on it.

23. Name the three tiny bones present in the middle part of the ear.

The three tiny bones – the malleus, incus, and stapes – are found in the middle ear. Each one is named in Latin for its shape.

24. What is the function of three tiny bones in the ear?

The three tiny bones help in transmitting the sound into the middle ear.

25. Name the nerve which carries electrical impulses from the cochlea of the ear to the brain.

The auditory nerve carries electrical impulses from the cochlea of the ear to the brain.

26. What is the name of passage in the outer ear which carries sound waves to the eardrum?

Sound waves are carried through the ear canal to the eardrum.

27. Name the quantity whose unit is ‘hertz’.

The unit of frequency is called “hertz”.

28. What is the relation between ‘time-period’ and ‘frequency’ of an oscillating body?

The time period is the reciprocal of the frequency.

Time period = 1/frequency.

29. Name three characteristics which are used to describe oscillations (or vibrations).

Frequency, amplitude and Phase are the three characteristics which are used to describe oscillations (or vibrations).

Page no: 254

30. What is the scientific name for the following?

The number of vibrations made per second

Frequency is the term used for the number of vibrations made per second.

31. What name is given to the maximum displacement of a vibrating body from its central position?

Amplitude is called as the maximum displacement of a vibrating body from its central position.

32. If 125 oscillations are produced in 5 seconds, what is the frequency in hertz?

Frequency f = No: of vibrations/time

= 125/5 = 25Hz

33. How does loudness depend on the amplitude of vibrations?

Amplitude and loudness are directly proportional. When loudness is high then the amplitude is high and vice versa.

34. By how much will the loudness of a sound change when the amplitude of vibrations is:

(a) doubled?

(b) halved?

(a) Loudness is also doubled.

(b) Loudness is halved.

35. Name the unit used to measure the loudness of sound. Also, write its symbol.

Decibel is the unit used to measure the loudness of sound. Its symbol is dB

36. What is the loudness of a normal conversation in decibels?

The loudness of normal conversation is 60dB.

37. On what factor does the pitch of a sound depend?

The frequency is an important factor which maintains the pitch of the sound.

38. How is pitch related to frequency?

Pitch and frequency are correlated in the means of the sound wave. The pitch of a sound is nothing but the frequency of the sound wave and if the pitch is high, the frequency will be high and vice versa.

39. Name the characteristic of sound which enables us to distinguish between a man’s voice and a woman’s voice even without seeing them.

The pitch of the sound enables us to distinguish between a man’s voice and a woman’s voice even without seeing them.

40. Arrange the following sounds in the order of increasing frequencies (keeping the sound of lowest frequency first) :

(i) Baby’s voice

(ii) Man’s voice

(iii) Woman’s voice

Man’s voice > Woman’s voice > Baby’s Voice

41. Which produces the sound of a higher pitch: a drum or a whistle?

Drums produce a higher pitch.

42. Name the characteristic of sound which depends on:

(a) Amplitude

(b) Frequency.

(a) The loudness of the sound depends on amplitude.

(b) Pitch of the sound depends on frequency.

43. Name the characteristic of sound which can distinguish between the ‘notes’ (musical sounds) played on a flute and a sitar (both the notes having the same pitch and loudness).

The tone will distinguish the notes (musical sounds) played on a flute and a sitar (both the notes having the same pitch and loudness).

44. Write the full form of dB.

Decibels is the full form of dB which is the unit of sound.

45. What is the name of very high-frequency sounds which cannot be heard by the human ear?

The ultrasonic wave is the name of very high-frequency sounds which cannot be heard by the human ear.

46. Why do we not hear the screams of a bat?

The frequency of bat scream is 20,000Hz. That is why we cannot hear the scream of a bat.

47. Which of the following frequency of sound can be heard by a dog but not by a man?

(a) 50,000 hertz

(b)15,000 hertz.

Option (a) is correct. 50,000Hz can be heard by a dog but not by a man.

48. Name the substance which vibrates in a flute to produce sound.

The air particles vibrate in the air column in the flute which further produces sound.

49. State whether the following statements are true or false:

(a) Sound cannot travel in a vacuum.

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

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

(d) The lower the frequency of vibration, the higher is the pitch.

(e) If the amplitude of vibrations is doubled, the loudness of sound also gets doubled.

(f) When the amplitude of vibrations is halved, the loudness of sound becomes one-fourth.

(g) Unwanted or unpleasant sound is termed as music.

(h) Noise pollution may cause partial hearing impairment.

50. Fill in the following blanks with suitable words :

(a) Sounds are produced by …………..objects.

(b) The human voice box is called …………..

(c) Sound cannot travel in ………………..

(d) A set of three tiny…………in the middle part of ear passes on sound vibrations from the eardrum to the liquid in the cochlea.

(e) The unit of frequency is …………..

(f) The time taken by an object to complete one oscillation is called…………

(g) The shrillness of a sound is determined by the ………..of vibration.

(h) Unpleasant sound is called……………….

(i) Sound which is pleasing to the ear is called…………….sound.

(j) A person having partial hearing loss can hear properly by wearing a device called hearing ……………on the ear.

(a) Sounds are produced by vibrating objects.

(b) The human voice box is called larynx

(c) Sound cannot travel in a vacuum

(d) A set of three tiny bones in the middle part of ear passes on sound vibrations from the eardrum to the liquid in the cochlea.

(e) The unit of frequency is Hertz (Hz)

(f) The time taken by an object to complete one oscillation is called time-period

(g) The shrillness of a sound is determined by the frequency of vibration.

(h) Unpleasant sound is called noise.

(i) Sound which is pleasing to the ear is called musical sound.

(j) A person having partial hearing loss can hear properly by wearing a device called a hearing machine on the ear.

Short Answer Type Questions

51. (a) What is the name of the strings in the human voice box which vibrate to produce sound?

(b) What makes these strings vibrate?

(a) The vocal chords of the human voice box vibrate to produce sound.

(b) The vocal chords are stretched across the larynx and they vibrate to produce sound.

52. Describe how sound is produced by the human voice box (or larynx).

Voicebox or larynx is a part of the throat which produces sound in humans. It has two vocal chords which are stretched across the larynx that it leaves a narrow slit between them for the air. When the lungs force the air through the slit, the vocal chord vibrates and produce sound

53. What is the frequency of the sound produced when the vocal cords are:

(a) tight and thin? (b) loose and thick?

(a) The frequency produced by tight and thin vocal chords is quite high. i.e. its high pitch sound.

(b) The frequency produced by loose and thick vocal chords is quite low i.e. its low pitch sound.

54. Why are the voices of men, women and children different?

The main reason for the difference in voices is the length of vocal chords. The longest vocal chord present in men and the shorter vocal chord is for women. Children have the smallest vocal chord.

55. If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?

We hear the vibrations from the ground when we put our ear at the track so that we can hear a train approaching from far away.

56. State one observation from everyday life which shows that sound travels much slower than light.

We see lightning first then the sound of thunder, because the velocity of light in air 3× 108 m/s while the velocity of sound in air is 343m/s.

57. Explain why the flash of lightning is seen first but the sound of thunder is heard a little later (though lightning and thunder take place in the sky at the same time and the same distance from us).

The flash of lightning is seen first but the sound of thunder is heard a little later (though lightning and thunder take place in the sky at the same time and the same distance from us) because the velocity of light in air 3× 108 m/s while the velocity of sound in air is 343m/s.

58. Name the object (or part) which vibrates to produce sound in the following musical instruments:

(d) Cymbals

(a) Strings

(b) Diaphragm – Membrane

(c) Air column

(d) The metal plates

(e) Strings

(f) Diaphragm – Membrane

59. Name one musical instrument each in which the sound is produced:

(a) By vibrating a stretched string.

(b) By vibrating air enclosed in a tube.

(c) By vibrating a stretched membrane

(d) By vibrating metal plates.

60. Give two examples of each of the following :

(a) Stringed musical instruments.

(b) Wind musical instruments.

(c) Membrane musical instruments.

(d) Plate type of musical instruments.

(a) Guitar, Veena

(b) Flute, Trumpet

(c) Tabla, Dholak

(d) Cymbals, Matka

Also, visit Lakhmir Singh Solutions for Class 8 Science to get complete solutions to all chapters.

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Sound of Class 8

Class 8 science notes.

The sound wave was discovered back as far as Leonardo da Vinci’s  (1452–1519) era. He discovered that sound travels in waves. He was a brilliant scientist, artist, and thinker and contributed many discoveries in the field of science. He was a man before his time who thought up inventions and ideas that came to be built far later by other engineers and scientists.

Christian Doppler later discovered that sound waves could be compressed or expanded, thereby, further expanding on da Vinci’s theory.

Sound waves have been rethought and the theory re-analyzed by many scientists throughout the years.

Sound and music are parts of our everyday sensory experience. Just as humans have eyes for the detection of light and color, so we are equipped with ears for the detection of sound.

Further Reading : 

2. Hearing Impairment

3. Human Ear

• sound wave physics
• Range of hearing
• Speed of sound in different medium
• Effect of temperature on the speed of sound
• Audible, ultrasonic and infrasonic waves
• what is Echo
• What is Noise
• Hearing impairment
• The human ear
• Solved questions
• Exercise 3 (True and False)
• Exercise 4 (Subjective)

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8 Ways to Create AI-Proof Writing Prompts

ChatGPT and other AI tools are smart but I’m smarter ... okay maybe not, but these are strategies for writing AI-proof writing prompts that I’ve used effectively in my classes.

Creating 100 percent AI-proof writing prompts can often be impossible but that doesn’t mean there aren’t strategies that can limit the efficacy of AI work. These techniques can also help ensure more of the writing submitted in your classroom is human-generated. 

I started seeing a big uptick in AI-generated work submitted in my classes over the last year and that has continued. As a result, I’ve gotten much better at recognizing AI work , but I’ve also gotten better at creating writing prompts that are less AI-friendly. 

Essentially, I like to use the public health Swiss cheese analogy when thinking about AI prevention: All these strategies on their own have holes but when you layer the cheese together, you create a barrier that’s hard to get through. 

The eight strategies here may not prevent students from submitting AI work, but I find these can incentivize human writing and make sure that any work submitted via AI will not really meet the requirements of the assignment. 

1. Writing AI-Proof Prompts: Put Your Prompt Into Popular AI tools such as ChatGPT, Copilot, and Bard 

Putting your writing prompt into an AI tools will give you an immediate idea of how most AI tools will handle your prompt. If the various AI chatbots do a good, or at least adequate, job immediately, it might be wise to tweak the prompt. 

One of my classes asks students to write about a prized possession. When you put this prompt into an AI chatbot, it frequently returns an essay about a family member's finely crafted watch. Obviously, I now watch out for any essays about watches. 

2. Forbid Cliché Use

Probably the quickest and easiest way to cut back on some AI use is to come down hard on cliché use in writing assignments. AI tools are essentially cliché machines, so banning these can prevent a lot of AI use. 

Equally as important, this practice will help your students become better writers. As any good writer knows, clichés should be avoided like the plague. 

3. Incorporate Recent Events

The free version of ChatGPT only has access to events up to 2022. While there are plugins to allow it to search the internet and other internet-capable AI tools, some students won’t get further than ChatGPT. 

More importantly, in my experience, all AI tools struggle to incorporate recent events as effectively as historic ones. So connecting class material and assignments to events such as a recent State of Union speech or the Academy Awards will make any AI writing use less effective. 

4. Require Quotes

AI tools can incorporate direct quotations but most are not very good at doing so. The quotes used tend to be very short and not as well-placed within essays. 

Asking an AI tool for recent quotes also can be particularly problematic for today’s robot writers. For instance, I asked Microsoft's Copilot to summarize the recent Academy Awards using quotes, and specifically asked it to quote from Oppenheimer's director Christopher Nolan’s acceptance speech. It quoted something Nolan had previously said instead. Copilot also quoted from Wes Anderson’s acceptance speech, an obvious error since Anderson wasn’t at the awards .  

5. Make Assignments Personal

Having students reflect on material in their own lives can be a good way to prevent AI writing. In-person teachers can get to know their students well enough to know when these types of personal details are fabricated. 

I teach online but still find it easier to tell when a more personalized prompt was written by AI. For example, one student submitted a paper about how much she loved skateboarding that was so non-specific it screamed AI written. Another submitted a post about a pair of sneakers that was also clearly written by a "sole-less" AI (I could tell because of the clichés and other reasons). 

6. Make Primary or Scholarly Sources Mandatory

Requiring sources that are not easily accessible on the internet can stop AI writing in its tracks. I like to have students find historic newspapers for certain assignments. The AI tools I am familiar with can’t incorporate these. 

For instance, I asked Copilot to compare coverage of the first Academy Awards in the media to the most recent awards show and to include quotes from historic newspaper coverage. The comparison was not well done and there were no quotes from historical newspaper coverage. 

AI tools also struggle to incorporate journal articles. Encouraging your students to include these types of sources ensures the work they produce is deeper than something that can be revealed by a quick Google search, which not only makes it harder for AI to write but also can raise the overall quality.  

7. Require Interviews, Field Trips, Etc. 

Building on primary and scholarly sources, you can have your students conduct interviews or go on field trips to historic sites, museums, etc. 

AI is still, thankfully, incapable of engaging in these types of behavior. This requires too much work for every assignment but it is the most effective way to truly ensure your work is human- not computer-written. 

If you’re still worried about AI use, you can even go a step further by asking your students to include photos of them with their interview subjects or from the field trips. Yes, AI art generators are getting better as well, but remember the Swiss cheese analogy? Every layer of prevention can help. 

8. Have Students Write During Class

As I said to start, none of the methods discussed are foolproof. Many ways around these safeguards already exist and there will be more ways to bypass these in the future. So if you’re really, really worried about AI use you may want to choose what I call the “nuclear option.” If you teach in person you can require students to write essays in person. 

This approach definitely works for preventing AI and is okay for short pieces, but for longer pieces, it has a lot of downsides. I would have trouble writing a long piece in this setting and imagine many students will as well. Additionally, this requirement could create an accusatory class atmosphere that is more focused on preventing AI use than actually teaching. It’s also not practical for online teaching. 

That all being said, given how common AI writing has become in education, I understand why some teachers will turn to this method. Hopefully, suggestions 1-7 will work but if AI-generated papers are still out of hand in your classroom, this is a blunt-force method that can work temporarily. 

Good luck and may your assignments be free of AI writing! 

• 7 Ways To Detect AI Writing Without Technology
• Best Free AI Detection Sites
• My Student Was Submitting AI Papers. Here's What I Did

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Erik Ofgang is Tech & Learning's senior staff writer. A journalist,  author  and educator, his work has appeared in the Washington Post , The Atlantic , and Associated Press. He currently teaches at Western Connecticut State University’s MFA program. While a staff writer at Connecticut Magazine he won a Society of Professional Journalism Award for his education reporting. He is interested in how humans learn and how technology can make that more effective. 

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