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Thursday 15 December 2022

Cbse class 8 - physics - sound - case study based question #class8science #sound #physics #eduvictors.

CBSE Class 8 - Physics - Sound - Case Study Based Question

Q1. Read the following and answer the questions given below:

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. Sound is produced by vibrating objects. Vibration can be described as to and fro motion of an objects. Sound cannot be produced without any vibrations. Sound always requires a medium to travel from the source of its production to the receiver end. Speed of the sound is maximum in solids and minimum in gases.

(i) The audible frequency range of a human ear is:

(a) The range of audible frequency of human ear is 20 to 200 Hz

(b) The range of audible frequency of human ear is 2 Hz to 20 Hz

(c)The range of audible frequency of human ear is 200 to 2000Hz.

(d) The range of audible frequency of human ear is 20 to 20,000Hz

(ii) Ria used a device to measure the loudness of a machine. She recorded her observation as given below. Which of the following represents the correct measurement of loudness?

(iii) Arrange the speed of sounds in solids, liquids and gases in an ascending order:

(a) Gas < Liquid < Solid

(b) Liquid > Gas > Solid

(c) Liquid < Solid < Gas

(d) Solid > Liquid > Gas

(iv) The number of vibrations made by a vibrating body in one second is:

(a) frequency

(c) loudness

1.  (d) The range of audible frequency of human ear is 20 to 20,000Hz

2.  (c) 80 dB

3.  (a) Gas < Liquid < Solid

4.  (a) frequency

Ch 13 - Sound (Q & A) Ch 13 - Sound (MCQs) Ch 13 - Sound (Worksheet) Ch 13 - Sound (Question Bank) Ch 13 - Sound (Worksheet)

CBSE All In One NCERT Based Science Class 8 2022-23 Edition

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Case Study Based Questions: Sound | Science Class 8 PDF Download

Imagine you're on a beach, and you hear the sound of ocean waves. These sound waves travel from the water to your ears. These waves travel through the air in the form of compressions and rarefactions, eventually reaching your ears.

Q1. What factors might affect the loudness and pitch of the waves? Ans: The loudness of sound waves is affected by the amplitude of the waves; greater amplitude results in louder sound. The pitch of the sound is determined by the frequency of the waves; higher frequency results in a higher pitch. In the context of ocean waves, the loudness may vary depending on the size and speed of the waves, as well as environmental factors like wind and distance. The pitch can be influenced by the wave's speed and the distance from the source.

Q2. Discuss the importance of protecting your ears from loud sounds. Ans: Protecting your ears from loud sounds is crucial to prevent hearing loss and damage. Prolonged exposure to loud noises can lead to conditions such as tinnitus (ringing in the ears) or permanent hearing loss. Loud sounds can damage the delicate hair cells in the inner ear, which are essential for hearing. Using ear protection, such as earplugs or earmuffs, and avoiding prolonged exposure to loud environments are important measures to safeguard hearing health.

Q3. Give examples of situations where sound can be harmful and explain the measures one can take to prevent hearing damage. Ans: Examples of harmful sound situations include: - Concerts or music events: High volume levels can damage hearing over time. Measures include using earplugs designed for musicians or limiting time spent in loud environments. - Construction sites: The noise from machinery and tools can be extremely loud. Wearing hearing protection like earmuffs or earplugs can prevent hearing damage. - Motor vehicles: The loud noise from engines and horns can be harmful. Using noise-cancelling headphones or ensuring proper vehicle maintenance can help reduce exposure to harmful noise levels. Fireworks displays : The sudden loud noise from fireworks can cause hearing damage. Watching from a distance and using ear protection can mitigate the risk.

Q4. Write about how different animals use sound for communication. Ans: Animals use sound for various forms of communication, which is essential for their survival and social interactions: Dolphins: They use a complex system of clicks, whistles, and burst-pulsed sounds to communicate with each other, navigate, and hunt. Birds: Many bird species use songs and calls to attract mates, defend territory, or communicate with flock members. Bats: They emit high-frequency echolocation calls to navigate and locate prey in the dark. Elephants: They produce low-frequency rumbles that can travel long distances, allowing them to communicate with other elephants over several kilometers. Dogs: They use barking, growling, and whining to express emotions, communicate with their owners, and interact with other dogs.

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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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Chapter 13 Class 8 - Sound

Click on any of the links below to start learning from Teachoo ...

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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NCERT Solutions Class 8 Science Chapter 13

Home » NCERT Solutions » NCERT Solutions Class 8 Science Chapter 13

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NCERT Solutions for Class 8 Science Chapter 13

Science is beneficial. Science produces powerful and trustworthy knowledge. It may be used to create new technology, treat diseases, and solve various other issues. The research is ever ongoing. Science is constantly improving and increasing our understanding of the cosmos, which raises new issues for future research. However, science can never be “completed.”

Quick Links

NCERT  Class 8 Science Chapter 13 is Sound. Students will be briefed on important issues that illustrate the relevance and role of Sound in our daily lives. The back-and-forth movement of an item is known as vibration. To travel, Sound needs a medium. As a result, it can’t travel through space. Therefore, sound is very vital in our lives.

Extramarks NCERT Solutions provide detailed and authentic answers to all the textbook questions. Through those, the students can understand, remember and retain answers to NCERT questions and thus, perform well in exams.

Going through the NCERT Solutions of each Chapter is a secret passage to achieve excellent results in the examination. To help the students, Extramarks has come up with the Class 8 Science Chapter 13 Solution. These solutions are made as per the requirements of students. Class 8 NCERT Solutions of Sound are written comprehensively.

At Extramarks, students have a variety to choose from. In addition, they can access several study materials for all classes. Material such as NCERT books, CBSE revision notes, CBSE sample papers, CBSE previous year question papers, and more are waiting for them at the Extramarks website.

Key Topics Covered in NCERT Solutions for Class 8 Science Chapter 13

Mentioning below the key concepts covered in NCERT Solutions for Class 8 Science Chapter 13- Sound:

Let us now look at Extramarks’ in-depth information on each subtopic in NCERT Solutions for Class 8 Science Chapter 13- Sound.

What is Sound?

Sound is described as vibrations that can travel through any material, such as air, and are audible when reaching an individual’s or animal’s ear. Musical Sound is described as a sound that is attractive to the ear, whereas Noise is defined as a jarring or unpleasant sound.

Sound is significant because it may take us in directions that vision alone cannot. It may also be significant since it can assist us in determining what we perceive. The Sound may also provide information about a character, location, and time. It facilitates communication between us. Simply hearing footsteps or hearing a voice might help us detect someone’s presence. NCERT Solutions for Class 8 Science Chapter 13 lets students know how important Sound is for a living being.

Sound Waves

NCERT Solutions for Class 8 Science Chapter 13 describes a sound wave as a pattern of disruption created by sound energy travelling away from its source. Longitudinal waves are sound waves where the direction of particle vibration is parallel to the path of energy wave transmission. The atoms vibrate back and forth when they are placed in a beat. A high-pressure and low-pressure zone in the medium occurs from this constant back and forth action. Compressions and rarefactions, respectively, are high-pressure and low-pressure zones.

Transverse Waves

• In Transverse waves, the particle’s direction of motion is perpendicular to that of wave motion.
• This Mechanical wave is a transverse wave, e.g., light, or even a Mexican wave at a stadium.

Longitudinal Waves

• When the medium’s particles migrate parallel to the wave motion’s direction through sequential compression or rarefaction.
• It’s a mechanical wave, too.
• Consider a slinky.

Types of Sound

As per the NCERT Solutions for Class 8 Science Chapter 13, Sound can be divided into two categories:

Inaudible Sound

The frequency of inaudible noises is over 20,000 Hz or below 20 Hz. A sound at this frequency level is inaudible to the typical human ear.

• Infrasonics are low-frequency noises that are inaudible to the human ear.
• Ultrasonics are high-frequency noises that are inaudible to the human ear.

Audible Sound

The audible noises are vibrations at 20 to 20,000 hertz (20 kHz). This frequency level is audible to the human ear.

Sound Properties

To travel, Sound needs a medium. A medium is a substance or material that allows Sound to travel.

Sound cannot travel in a vacuum. 

Characteristics of Sound

Extramarks NCERT Solutions for Class 8 Science Chapter 13 discusses the three fundamental characteristics of Sounds in the following:

• Loudness: Loudness is an acoustic feeling that allows people to discern between faint and loud sounds. The Sound generated will be more perceptible if the amplitude of vibrations is greater. This is because the cube of the amplitude of a wave is exactly proportional to its loudness.
• Pitch: Pitch is a sound property that allows people to discriminate between soft and harsh sounds. The vibration frequency is directly proportional to the pitch and shrillness and increases or decreases with it.
• Quality: Quality is a sound quality that allows people to discern between musical sounds produced by different singers or musical instruments, even if their volume and pitch are the same.

Sounds by Humans

How do Humans Produce sounds?

To answer this question, Extramarks NCERT Solutions for Class 8 Science Chapter 13 states:

• The larynx generates the Sound, positioned at the top of the windpipe.
• In the voice box, two vocal cords span across each other and have a slot through which the lungs push air out.
• The voice cords’ muscles control how tight or loose they are.

Extramarks’ NCERT class 8 science chapter 13 explains that the human ear comprises three parts: External Ear, Middle Ear, and Internal Ear.

• Pinna (outer ear) collects Sound from the environment.
• The auditory canal is like a tube through which Sound travels.
• When Sound strikes the eardrum (tympanic membrane), it vibrates.
• Vibrations are sent to the inner ear, and after receiving, they send signals to the brain through the auditory nerve.

Amplitude, Time Period and Frequency

Extramarks’ NCERT Solutions for Class 8 Science Chapter 13 explains the concept of Amplitude, Time Period and Frequency in the following points:

The maximum extent of vibrations produced by any vibrating body from its mean location is amplitude. The amount a radio wave goes back and forth is an example of amplitude.

Time Period

An oscillation is a full to-and-fro movement of the pendulum from its mean position. The Time Period is the time it takes for a vibrating particle to complete one oscillation.

Frequency is the number of oscillations per second—Hertz unit of measurement (Hz).

Noise Pollution

Noise pollution is often characterised as repeated exposure to high sound levels that cause harm to people or other living beings. However, according to the World Health Organization, sound levels below 70 decibels do not harm living beings, regardless of how long or constant the exposure is.

Unwanted Sound (Noise) may be harmful to one’s health. Cardiovascular problems, hypertension, excessive stress levels, tinnitus, deafness, sleep difficulties, and various other detrimental and unsettling impacts are all linked to sound pollution. Environmental Noise or noise pollution is the spread of Noise that has multiple effects on human or animal life activities, most of which are damaging to some extent.

Outside Noise is mainly created by machines, transportation, and propagation systems. Poorly designed urban areas can often 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, construction, electrical generators, explosions, and other people are some of the most common noise sources in residential neighbourhoods. Noise can increase the risk of mortality in animals by disrupting predator and prey detection and avoidance, interfering with reproduction and navigation, and contributing to irreversible deafness. The water absorbs a large portion of the Noise that humans make.

Experts have focused on noise pollution in NCERT Solutions for Class 8 Science Chapter 13 straightforwardly, which will help students understand how excessive and undesired sounds the source of noise pollution may be. The noise pollution is caused mainly by human-made voices. Bursting crackers, loudspeakers, and the Sound of automobiles are the most common sources of noise pollution.

NCERT Solutions for Class 8 Science Chapter 13 Exercise and Solutions

Extramarks’ website is full of quality study material. Great resources such as previous year’s question papers, revision notes, extra problems, and more are available for all the classes. Click on the below links to view NCERT Solutions for Class 8 Science Chapter 13:

• Class 8 Science Chapter 13: Very Short Answer Type Questions
• Class 8 Science Chapter 13: Short Answer Type Questions
• Class 8 Science Chapter 13: Long Answer Type Questions

Extramarks NCERT solutions provide detailed and authentic answers to all the textbook questions. Through those, the students can understand, remember and retain answers to NCERT questions and thus, perform well in exams.

Students can easily access NCERT Solutions for Class 8 Science Chapter 13 and other chapters by clicking here . In addition, students can also explore NCERT Solutions for other classes below.

By getting access to NCERT Solutions for Class 8 Chapter 13, students can easily understand all the concepts of Sound.

NCERT Solutions Class 8 Science Chapter-wise List

Key Features of NCERT Solutions for Class 8 Science Chapter 13

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Q.1 Choose the correct answer.

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

The correct option is (d).

Explanation: Sound cannot travel through vacuum. Solids, liquids and gases provide the medium for sound to travel.

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

(a) Baby girl (b) Baby boy (c) A man (d) A woman

The correct option is (c).

Explanation: The pitch of an adult man is lower as compared to baby boy, baby girl and woman. Also, frequency of a sound is directly proportional to its pitch. Hence, man’s voice is of minimum frequency in this case.

Q.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. (T/F) (b) The number of oscillations per second of a vibrating object is called its time period. (T/F) (c) If the amplitude of vibration is large, sound is feeble. (T/F) (d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F) (e) The lower the frequency of vibration, the higher is the pitch. (T/F) (f) Unwanted or unpleasant sound is termed as music. (T/F) (g) Noise pollution may cause partial hearing impairment. (T/F)

(a) Sound cannot travel in vacuum. (T) Explanation: Sound travels in the presence of a medium. (b) The number of oscillations per second of a vibrating object is called its time period. (F) Explanation: 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. (F) Explanation: Loudness of a sound is directly proportional to the square of the amplitude of its vibration. When the amplitude of vibration of a sound is large, the sound is called very loud. The sound is feeble for small amplitude. (d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T) Explanation: A human can hear a sound whose frequency comes in the range of 20 Hz − 20,000 Hz. (e) The lower the frequency of vibration, the higher is the pitch. (F) Explanation: The pitch of a sound is proportional to its frequency. (f) Unwanted or unpleasant sound is termed as music. (F) Explanation: Unwanted or unpleasant sounds are known as noise. (g) Noise pollution may cause partial hearing impairment. (T) Explanation: When a loud and unpleasant sound is produced continuously for a long time, then it may affect temporarily our hearing impairment.

Q.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.

(a) Time taken by an object to complete one oscillation is called time period . (b) Loudness is determined by the amplitude of vibration. (c) The unit of frequency is hertz (Hz) . (d) Unwanted sound is called noise . (e) Shrillness of a sound is determined by the frequency of vibration.

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

Number of oscillations = 40 Total time taken = 4 s The number of oscillations per second is called frequency . ∴   Frequency = Number   of   oscillations Total   time   taken = 40 4   s = 10   Hz ⇒   Time   period   =   1 Frequency = 1 10   Hz = 0 .1   s MathType@MTEF@5@5@+=feaaguart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0le9yqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=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@F8AD@

Q.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?

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

(a) Dholak: It is a musical instrument which consists of a stretched membrane known as its head. When the head is beaten softly, the stretched membrane sets into vibration. Hence, the dholak produces a sound when it is beaten. (b) Sitar: It is also a musical instrument which consists of stretched strings. When a string is plucked, it sets into vibration. Hence, the sitar produces sound when it is beaten. (c) Flute: It is a hollow pipe. When air is blown over its mouth, the air inside the pipe is set into vibration. Thus, a pleasant sound is produced.

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

Music: The sound which seems pleasant to ear is called music. For example, the sound produced by violins, pianos, flutes, etc.

Noise: The sound which seems unpleasant to ear is called noise. For example, sound produced by horns of buses and trucks, sound of electrical generators, sound of a gunshot, etc.

Yes. When music is played at very high volume, it becomes noisy.

Q.9 List sources of noise pollution in your surroundings.

The sources of some noise pollution are as follows:

• Horns of vehicles
• Loudspeakers

Q.10 Explain in what way noise pollution is harmful to human.

Noise pollution can cause stress, hypertension, insomnia, hearing loss, etc.

Q.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.

There will be more noise around the house which is located along the roadside. The effect of noise decreases with the distance between the source and the listener. Thus, it is better to choose the house that is three lanes away from the roadside.

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

In human beings, sound is produced by the voice box or larynx ,which is at the upper end of the windpipe. Two vocal cords are stretched across the larynx. These vocal cords leave a narrow slit between them for the passage of air. The air from the lungs passes through the slit due to which vocal cords starts vibrating. As we know that vibration of an object is the necessary condition for the production of sound, so the sound is produced due to vibrations of the vocal cords.

Muscles attached to the vocal cords can make the cords tight or loose and can change the type or quality of the voice produced.

Q.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?

The speed of light is more than the speed of sound. Therefore, light reaches us before thundering.

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Faqs (frequently asked questions), 1. what is the central idea of the 13th chapter of class 8 science.

Chapter 13 of the NCERT Solutions for Class 8 Science Chapter 13 helps to teach students about the process that causes the Sound to be produced. Anything that vibrates causes disruptions in the medium around it. This surrounding medium carries the disruptions or waves to the human ear. Therefore, the Sound generated will be perceptible if the frequency of the waves is within the human hearing range. This is the central idea of this Chapter.

2. How do we tell the difference between music and Noise?

 Music is an aesthetically pleasing sound. It is made up of uniform spacing and rhythmic essential overtones and frequencies. Noise is sound that has no discernible structure. It’s inconsistent and irregular, and it’s unpleasant to listen to. The Sound generated by musical instruments, for example, is music, but the Sound created by vehicles is Noise.

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NCERT Exemplar Class 8 Science Chapter 13 Sound

June 20, 2022 by Sastry CBSE

NCERT Exemplar Class 8 Science Chapter 13 Sound are part of NCERT Exemplar Class 8 Science . Here we have given NCERT Exemplar Class 8 Science Chapter 13 Sound.

Multiple Choice Questions (MCQs)

Question 1 A list of mediums is given below (i) Wood (ii) Water (iii) Air (iv) Vacuum In which of these mediums can sound travel? (a) (i) and (ii) (b) (i), (ii) and (iii) (c) (iii) and (iv) (d) (ii), (iii) and (iv) Answer. (b) Sound requires any medium to travel but in vacuum there is no medium, so sound cannot travel through them.

Question 2 The loudness of sound depends on (a) its amplitude (b) its time period (c) its frequency (d) its speed Answer. (a) Sound will be loud when its amplitude is large and sound will be soft when its amplitude is small hence, loudness of sound depends upon its amplitude.

Question 3 Which of the following statements are correct? (i) Sound is produced by vibrations. (ii)Sound requires a medium for propagation. (iii)Light and sound both require a medium for propagation. (iv)Sound travels slower than light. (a) (i) and (ii) (b) (i), (ii) and (iii) (c) (ii), (iii) and (iv) (d) (i), (ii) and (iv) Answer. (d) Because light can travel in vacuum also but it is only sound which requires medium to travel.

Question 5 order to reduce the loudness of a sound, we have to (a) decrease its frequency of vibration of the sound (b) increase its frequency of vibration of the sound (c) decrease its amplitude of vibration of the sound (d) increase its amplitude of vibration of the sound Answer. (c)Since, loudness depends upon amplitude, so it can be increased by increasing amplitude and it can be decreased by decreasing amplitude.

Question 6 Loudness of sound is measured in units of (a) decibel (dB) (b) hertz (Hz) (c) metre (m) (d) metre/second(m/s) Answer. (a) Unit of loudness of sound is decibel (dB). ,,

Question 7 The loudness of sound is determined by its (a) amplitude of vibration (b) ratio of amplitude and frequency of vibration •(c) frequency of vibration (d) product of amplitude and frequency of vibration Answer. (a) Loudness of sound is determined by the amplitude of its vibrations.

Question 8 1 Hz 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) 1 Hz = 1 vibration per second = 60 vibrations per minute

Question 9 Pitch of sound is determined by its (a) frequency (b) speed (c) amplitude (d) loudness Answer. (a) Pitch or shrillness is determined by the frequency of sound.

Question 10 Ultrasound has frequency of vibration (a) between 20 and 20000 Hz (b) below 20 Hz (c) above 20000 Hz (d) between 500 and 10000 Hz Answer. (c) Ultrasound has frequency of vibration above 20000 Hz.

Question 12 Does any part of our body vibrate when we speak? Name the part. Answer. Yes, while speaking the part which vibrates is called vocal cords. It is below the throat and creates vibrations while speaking.

Question 13 Boojho saw a cracker burst at night at a distance from his house. He heard the sound of the cracker a little later after seeing the cracker burst. Give reason for the delay in hearing the sound. Answer. The light travels faster than sound. So, the light from the cracker reaches faster than that of sound of the cracker. Speed of light in air = 3 x 108 m/s Speed of sound in air = 330 m/s

Question14 When we hear a sound, does any part of our body vibrate? Name the part. Answer. Yes, It is the eardrum which vibrates and sends vibrations to the inner ear, when we hear any sound.

Question 15 Name two musical instruments which produce sound by vibrating strings. Answer. Guitar and sitar are the two musical instruments which produce the sound by vibrating strings.

Question 17 We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us. Answer. Since, range of frequency for every vibrating body is different. But we can hear the vibrations which lies between the range of frequencies from 20 Hz to 20000 Hz, so sound of every vibrating body cannot be heard by us.

Question18 Suppose a stick is struck against a frying pan in vacuum. Will the frying > pan vibrate? Will we be able to hear the sound? Explain. Answer. Yes, the frying pan will vibrate. Since, it is being hit by the stick but vibrations need a medium to travel and there is no medium in vacuum, so we’cannot hear the vibrations produced.

Question19 Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons. Answer. No, they cannot talk to each other without using any special device because there is no medium in space and sound needs medium to travel.

Question20 List three sources of noise pollution in your locality. Answer. Sources of noise pollution gre . (i) Horns of vehicles (ii)Loudspeakers of temples (iii)Generators running without silencers

Question 21 We have a stringed musical instrument. The string is plucked in the middle first with a force of greater magnitude and then with a force of  smaller magnitude. In which case would the instrument produce a louder sound? Answer. It will create more loud sound in case of string stretched with a greater force because amplitude is greater in this case and loudness depends on the amplitude. Greater will be the loudness, greater will be the amplitude.

Question 22 How is sound produced and how is it transmitted and heard by us? Answer. Sound is produced when any object starts vibrating by any means. These vibrations travel from the source all around the environment through the particles of the environment, thus, it reaches to its destination, i.e. our ear. Now, it enters our ear and travels down a canal at the end of which a thin membrane is stretched tightly known as eardrum. The eardrum sends vibrations to inner part of the ear and finally reaches to the brain and we hear the sounds.

Question 24 The town hall building is situated close to Boojho’s house. There is a clock on the top of the townhall building which rings the bell every hour. Boojho has noticed that the sound of the clock appears to be much clearer at night. Explain. Answer. We know that speed, pitch, loudness all are initiated with a vibration. During the day, there is a number of vibrations around us. So, the sound coming from the clock gets disturbed and amplitude of vibrations becomes small. But during the night, there are not such multiple vibrations in the environment. So, sound is more clear. Further,-“the dew factor at night increases the speed of sound as moisture level increases.

Long Answer Type Question

Question 25 Suggest three measures to limit noise pollution in your locality. Answer. The following measures to limit noise pollution in our locality is given as: (i) The industries which produce noise should be setup away from the residential areas. (ii)The television and the music systems should be run at the low volumes. (iii)The aircraft engines, transport vehicles, industrial machines and home appliances ’ must be installed with siltncing devices.

NCERT Exemplar Class 8 Science Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials : Metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Combustion and Flame
• Chapter 7 Conservation of Plants and Animals
• Chapter 8 Cell Structure and Functions
• Chapter 9 Reproduction in Animals
• Chapter 10 Reaching the Age of Adolescence
• Chapter 11 Force and Pressure
• Chapter 12 Friction
• Chapter 13 Sound
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water

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Important Questions for CBSE Class 8 Science Chapter 13 - Light

• Class 8 Important Question
• Chapter 16: Light

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

The important questions for class 8 science chapter 13 PDF available on the Vedantu website for easy access and students can download the PDF anytime. The important questions for Class 8 Science chapter 13 PDF cover every topic from chapter 13 of class 8 science. It will be helpful for students for fetching a good score in their academic exams. The Class 8 Science chapter 13 important questions are designed for the students in such a way that they will be able to understand the concepts with clear understanding. Vedantu is a platform that provides free CBSE Solutions (NCERT) and other study materials for students. Maths Students who are looking for better solutions can download Class 8 Maths NCERT Solutions to help you to revise the complete syllabus and score more marks in your examinations.

Study Important Questions for Class 8 Science Chapter 13 – Light

1. When all the parallel rays reflected from a rough or irregular surface are not parallel, the reflection is known as ___________.

A. multiple reflections                                 B. regular reflection

C. lateral inversion                                       D. diffused reflection 

Ans: D. diffused reflection.

2. The angle between normal and incident rays is called the ___________________. 

A. angle of incidence                                     B. angle of reflection 

C. angle of refraction                                    D. normal 

Ans: A. angle of incidence

3. Which part of the eye protects the interior from accidents? 

A. pupil                                                              B. retina 

C. cornea                                                           D. rods 

Ans: C. Cornea protects the eye's sensitive components from dirt, bacteria, and other foreign particles.

4. Which one of the following works on the basis of multiple reflections?  

A. kaleidoscope B. microscope C. telescope D. periscope 

Ans:  A. Kaleidoscope. A kaleidoscope is an optical device containing two or more reflecting surfaces that are angled at an angle to each other.

5. Angle of incidence is __________equal to the angle of reflection

A. Sometimes                                                  B. Never

C. always                                                          D. almost  

Ans: C. Always

6. White light consist of ___________ colours 

A. six                                                                   B. seven 

C. eight                                                               D. nine 

Ans: B. Seven. Red, orange, yellow, green, blue, indigo and violet are the colors that make up white light.

7. Image formed in a plane mirror undergoes _______________. 

Ans: lateral inversion. The reversal of a mirror image, where the right side of the object appears on the left side behind the mirror, is known as lateral inversion.

8. Name the part of the eye which gives distinctive color. 

Ans: Iris is the part of the eye that gives distinctive color. The iris is a colored ring that surrounds our pupils and gives our eyes their distinct color.

9. The lens focuses light on the back of the eye, on a layer called___________. 

Ans: Retina. Thousands of light-sensitive cells (rods and cones) and other nerve cells make up the retina, which receives and organizes visual data. Through your optic nerve, your retina conveys this information to your brain, allowing you to see.

10. What is a blind spot?

Ans: There are no sensory cells at the intersection of the optic nerve and the retina, hence vision is impossible there. This is referred to as the blind spot.

11. ____________ are sensitive to bright light in eye.

Ans: Cones. In the retina, cones are a type of photoreceptor cell. They are responsible for our color perception. Cones are concentrated in the macula, which is located in the center of our retina and helps us see small details.

12. Lack of which nutrient is responsible for eye troubles?

Ans: Deficiency of Vitamin A causes eye troubles. Xerophthalmia is a progressive eye disease caused by a lack of vitamin A. Xerophthalmia can progress to night blindness or more serious damage to the cornea, the outer layer of the eye. 

13. Some persons may lose their eyesight because of a _________ or an __________. Ans: Disease, injury.

14. Who developed a system for visually challenged persons and published it in 1821? Ans: Braille was developed in the 1820s by Louis Braille and is the most widely used resource for visually impaired people. Louis Braille. Blind individuals read and write using the Braille system. A set of raised bumps or dots can be sensed with a finger in the Braille system.

15. Do you think a ray of light is an idealization? Why? 

Ans: Yes a ray of light is an idealization. In reality, there is a narrow beam of light that is made up of several rays. For simplicity, the term ray is used for a narrow beam of light.

16. Give any two uses of periscope. 

Ans: Submarines, tanks, and soldiers in bunkers use periscopes to see things outside. 

17. ___________ system helps visually challenged persons to read and write. 

Ans: Braille. Braille is a written language for the blind in which characters are represented by patterns of raised dots that can be felt with their fingertips.

18. The impression of an image does not vanish immediately from the retina. It persists there for about ___________of a second.

 Ans: 1/16 th

19. a. Define dispersion of light. 

 Ans: Dispersion of light is referred to as splitting of light into its constituent colors.  

 b. Give an example of dispersion.

   Ans: Rainbow is a natural phenomenon that shows dispersion. 

20. Define the following, 

a. Incident ray 

Ans: a. Incident ray is defined as a light ray, which strikes any surface.       

b. reflected ray.

Ans: The ray that returns from the surface after it has been reflected is known as the reflected ray.

The angle of incidence equals the angle of reflection, according to the law of reflection.

21. List the food items which contain vitamin A.

Ans: Vitamin A is abundant in raw carrots, broccoli, and green vegetables (such as spinach) as well as cod liver oil. Vitamin A is found in foods including eggs, milk, curd, cheese, butter, and fruits like papaya and mango.

22. State laws of reflection.

Ans: ‘The angle of incidence is always equal to the angle of reflection,' says the first law of reflection.

The incident rays reflected rays, and normal rays are drawn at the point of incidence to the reflecting surface all lie in the same plane, according to the second law of reflection. 

23. Give any four examples of luminous objects.

 Ans: The Sun, fire, the flame of a candle, and an electric lamp are examples of luminous objects.

24. Describe regular reflection with the help of a diagram. 

Ans: Regular reflection is a reflection from a smooth surface such as a mirror. Regular reflection creates images.

25. What is the function of the retina? 

Ans: The lens directs light to the retina, which includes a number of nerve cells. The nerve cells' sensations are subsequently transferred to the brain via the optic nerve. 

26. Given an example to show that reflected light can be reflected again. 

Ans: Stand in front of a mirror and tell a friend to hold a mirror behind you so you can see your haircut; your hair picture will appear in the mirror in front of you; this is the best example of reflected light returning to the source.

27. Can we see objects in dark? Why? 

Ans : When light reflected by an object reaches our eyes, we can see it. However, when there is no light reflected by the object, we cannot see it.

28. How does the braille system work?

Ans: There are 63 dot patterns or characters in the Braille system. A letter, a combination of letters, a common word, or a grammatical sign is represented by each character. Dots are arranged in cells of two vertical rows of three dots each. Below are various dot patterns that symbolize English letters and common words.

When embossed on Braille sheets, these patterns assist visually impaired people in recognizing words by touch. The dots have been slightly right to make them easier to touch.

29. Explain the structure of the eye with a neat labeled diagram.

Ans: The shape of the eye is generally spherical. The eye's outer layer is white. It is tough in order to protect the interior of the eye from damage. The cornea is the translucent front section of the eye. The iris is a dark muscular tissue that lies behind the cornea. The pupil is a tiny aperture in the iris that allows light to pass through. The iris regulates the size of the pupil. The iris is the colored portion of the eye.

30. How do you make a kaleidoscope?

Ans: Get three rectangular mirror strips, each about 15 cm long and 4 cm broad, to build a kaleidoscope. To make a prism, join them together. Place the mirrors in a circular cardboard tube or a tube made of thick chart paper. Assemble the tube so that it is slightly longer than the mirror strips. Close one end of the tube with a cardboard disc with a hole in the middle that you can see through. Put a piece of the transparent plastic sheet under the cardboard disc to make it more durable. Fix a round plane glass plate at the opposite end, touching the mirrors. Place numerous little pieces of colored glass on this glass plate (broken pieces of colored bangles). A ground glass plate is used to close this end of the tube. Make sure there's enough space for the color pieces to move around. Now, the kaleidoscope is ready to use.

31. Demonstrate an activity to show that the angle of incidence is always equal to the angle of reflection.

Ans: On the paper, draw lines to illustrate the position of the plane mirror, incident ray, and reflected ray. At the place where the incident ray reaches the mirror, draw a line at a 90o angle to the line representing the mirror. The normal to the reflecting surface at that location is this line. The angle of incidence and the angle of reflection should be measured. Change the angle of incidence and repeat the activity multiple times. The angle of incidence is always equal to the angle of reflection when the experiment is accurately carried out.

32. Write any five ways to take care of your eyes.

Ans: Some possible measures to take care of the eyes are as follows:

Use appropriate eyewear if advised.

It is harmful to the eyes to have too little or too much light. Eye strain and headaches are caused by insufficient light. The retina can be damaged by too much light, such as that of the Sun, a strong lamp, or a laser torch.

Do not look directly at the Sun or bright light. 

Do not rub your eyes. If dust particles get into your eyes, rinse them out with clean water. If your condition does not improve, see a doctor.

Always read at a comfortable distance for your eyes. Avoid bringing the book too close to your eyes or keeping it too far away when reading.

Important Questions Class 8 Science Chapter 13

Class 8 science ch 13 extra questions.

The class 8 science ch 13 extra questions cover all the important concepts from chapter 13 of class 8 science. Chapter 13 of class 8 deals with the concepts of light and given an introduction to the world of physics. Physics is a branch of science that deals with the study of nature. When we study the concepts of physics we must keep in mind that we are going to study what we will be experiencing in our day-to-day lives. For understanding chapter 13 students are suggested to prepare with quality material and reliable content like class 8 science chapter 13 important questions. The important questions class 8 science chapter 13 Pdf material provided here gives a deep insight into the class 8 science chapter 13.

Students can master any difficult subject or topic with the practice of relevant questions. The class 8 science ch 13 extra questions provided here will boost students’ confidence and their exam preparation. The class 8 science chapter 13 important questions incorporated all kinds of questions that will be helpful for the students in understanding the concepts in a better way. Before going through class 8 science ch 13 extra questions let us have a look at what this chapter includes and what we are going to learn from chapter 13 of class 8 science.

The class 8 science chapter 13 deals with the concepts of light. We know that Light is an important natural phenomenon in our lives, we can say it is one of the important senses of human life. Everything we are able to see is only because of the presence of light. Chapter 13 has given a detailed description of the concept of light and the laws of physics. It explains why the sense of sight is an essential part of every living thing. Because of the light, we are able to see what is happening around us, we are able to witness the beauty of our nature because of the sight. The content you are going through on the screen can be read-only because of the light. Thus sight is an essential sense among all the senses.

The chapter Light begins with the concepts and meaning of the light and laws of reflections. Students might have already come across the word like the reflection in the previous chapter, in this unit students learn what is reflection and what are the laws associated with the reflection. This chapter will give answers to the most common questions that arise in students like how can a visually disabled person read? How an owl can see only in the night but not during the daylight? What is a braille system is also explained in chapter 13 of class 8 physics. These questions can find the detailed solution from the class 8 science ch 13 extra questions.

In this chapter students will also learn about the human eye, the construction of the human eye. Students will also learn some interesting experiments for explaining the reflection such as the construction of a kaleidoscope. By the end of the chapter, students will be capable of answering many interesting concepts, and in addition to their preparation, important questions for class 8 science chapter 13 Pdf will be a brownie point.

What are the Benefits of Important Questions from Vedantu for Class 8 Science Chapter 13 - Light

Explore the advantages of Vedantu's Important Questions for Class 8 Science Chapter 13 - Light. These curated questions provide a strategic approach to mastering key concepts, ensuring comprehensive understanding and effective exam preparation. Here are few points that describe the Benefits of Important Questions from Vedantu for Class 8 Science Chapter 13 - Light:

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The study material provided here is important questions class 8 science chapter 13 Pdf is prepared by the experts according to the prescribed syllabus. It includes MCQ types of questions, diagram-oriented questions, short and long answer questions, along with class 8 science ch 13 extra questions. Students are advised to register to the Vedantu today and get access to the unlimited and extended study materials of the desired topics.

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

1. What is the way to take care of your eyes?

Ans:  Eyes are very important and proper care should be taken for protection.

If you are advised to use the spectacles make sure to use the suitable and the correct spectacles.

Keep the spectacles always clean.

Don’t let your eyes be exposed to too much light. This will lead to damage to the retina.

Never look directly to the sunlight or any powerful dazzling light. It will be harmful.

While reading a book keep it at a proper distance, don’t get too close to the eyes.

If the dust particles go inside your eyes do not rub them, just wash with clean water.

2. Mention the function of the parts of the eye.

Ans: The main parts of the human eye are Cornea, Iris, Pupil, Lens, Retina and Optic nerve. The thin layer where the light enters the eye and which forms a transparent bulge is called Cornea. A dark muscular diaphragm whose function is to control the size of the pupil is called Iris. The function of the lens is to adjust the focal length which is required to focus on the object according to the distances.

A Retina is a very sensitive and delicate membrane where the images are formed and has many photosensitive cells called rods and cones. Rods are sensitive to dim lights and cones are sensitive to bright lights.

The function of the optic nerve is to transmit the electric signals from the eye to the brain.

3. What do you understand about the Braille System?

Ans:  Certain people are affected usually whom we say as visually impaired due to many reasons.  The term Braille system is used to help visually impaired persons to read and write.  This contains 63 dot patterns or we can say as the characters. These characters are on the Braille sheets which can be easily recognized by the touch. These characters slightly bulge so the persons can feel the characters.

4. What are the laws of reflection?

Ans:  The definition of the law of reflection is when the light falls on any smooth surface the angle of reflection is equal to the angle of incidence and the incident ray, the normal to the surface and the reflected ray all lie in the same plane.

The laws of reflection state that

The angle of reflection is equal to the angle of the incident to the line perpendicular to the surface of the point of contact.

The reflected ray is always in the plane which is defined by the ray of the incident to the surface of the point of contact.

5. Define regular and irregular reflection?

Ans: Regular reflections are produced by the plane mirrors with smooth surfaces. The image produced by the regular reflection is always clear and visible. The images are virtual and we cannot collect the image on the screen.

Irregular reflections are produced by the rough surfaces. In this reflection, the illuminated objects are seen from any position. In this type of reflection, the parallel incident light rays are reflected irregularly in many directions. 

To know more about  Chapter 13 - Light of Class 8 Science refer to the notes provided by Vedantu . They are available on the website of Vedantu and their App and that too free of cost.

Chapterwise Important Questions for CBSE Class 8 Science

Cbse study materials.

NCERT Solutions for Class 8 Science Chapter 13 Sound

NCERT Solutions for Class 8 Science Chapter 13 Sound are given below. Here we have provided the best and error-free answers to all the exercise questions that will strengthen your foundation in science. Solving NCERT questions will assist you in grasping the content in the Crop Production and Management chapter in a better way.

In these solutions, we have answered all the intext and exercise questions provided in NCERT class 8 science textbook.  NCERT Solutions for Class 8 Science Chapter 13 Sound provided in this article are strictly based on the CBSE syllabus and curriculum. Students can easily download these solutions in PDF format for free or can read them online.

Sound Class 8 Science NCERT Solutions

Exercise Questions

Question 1: Choose the correct answer: 

Sound can travel through 

(a) gases only (b) solids only  (c) liquids only (d) solids, liquids and gases.

Answer: (d) solids, liquids and gases.

Explanation: Sound requires a medium to travel through. Solid, liquid and gas provide the medium for sound. Hence, sound can travel through 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: (c) A man 

Explanation: 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. (T / F)

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

(c) If the amplitude of vibration is large, sound is feeble. (T / F)

(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T / F)

(e) The lower the frequency of vibration, the higher is the pitch. (T / F)

(f) Unwanted or unpleasant sound is termed as music. (T / F)

(g) Noise pollution may cause partial hearing impairment. (T/F)

Sound requires a medium to travel through. Since vacuum is devoid of any medium, sound cannot travel through it.

The number of oscillations per second of a vibrating object is known as its frequency. Time period is the time required to complete one oscillation.

Loudness of a sound is proportional to the square of the amplitude of its vibration. When the amplitude of vibration of a sound is large, the sound is very loud. The sound is feeble for small amplitude.

Humans cannot hear sounds of all frequencies. Humans can hear a sound whose frequency falls in the range of 20 Hz−20,000 Hz. The sound having frequency out of this range is inaudible to humans.

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. A sound is said to be high pitched if its frequency of vibration is high, and is low pitched for a small frequency of vibration.

Unwanted or unpleasant sounds are known as noise. Sounds that are melodious and pleasing to ear are known as music.

Unwanted or unpleasant sounds are known as noise. If one is subjected to loud unpleasant sound continuously for a long time, then it may cause temporary hearing impairment.

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

(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) The 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: Here no. of oscillation = 40 Time taken = 4s

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:  

(a) Dholak: Dholak has stretched membranes which vibrate to produce sound.

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

(c) 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: 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: Some sources of noise pollution are as follows:

(i) Televisions and transistors running at high volumes

(ii) Loudspeakers and crackers

(iii) Horns of buses, cars and trucks

(iv) Home appliances such as mixer, desert cooler, etc.

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: There will be more noise in the house which is along the roadside. This is because noise produced by transportation vehicles may cause trouble to the residents. The intensity of noise decreases with the distance between the source and the listener. Hence, it is better to take the house that is three lanes away from the roadside. 

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

Answer: When we swallow something, the larynx moves.  There are two vocal cords inside the larynx. The air passes through a small gap which is present in between them. The lungs force the air into the gap when we speak and this vibrates the vocal cord, due to which sound is produced.

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. 

NCERT Solutions for Class 8 Science Chapter 13 – A Brief Discussion

CBSE Class 8 Science NCERT Solutions Chapter 13 helps students to clear their doubts and to score good marks in the board exam. All the questions are solved by experts with a detailed explanation that will help students complete their assignments & homework. Having a good grasp over CBSE NCERT Solutions for Class 8 Science will further help the students in their preparation for board exams and other competitive exams such as NTSE, Olympiad, etc.

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MCQ Questions for Class 8 Science Chapter 13 Sound

• Last modified on: 1 year ago
• Reading Time: 16 Minutes

Here we are providing mcq questions for class 8 science. In this article, we are covering Class 8 Science Chapter 13 Sound.

Question 1. 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

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

Question 3. Pitch of sound is determined by its (a) frequency (b) speed (c) amplitude (d) loudness

Question 4. 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.

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

Question 6. 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

Question 7. The voice box is also called as (a) stomach (b) heart (c) larynx (d) mouth

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

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

Question 10. Speed is (a) Distance travelled / Time (b) Time / Distance travelled (c) Distance travelled × Time (d) Time + Distance travelled

Question 11. Loudness of sound is determined by (a) pitch (b) frequency (c) amplitude (d) time period

Question 12. The number of vibrations made by a vibrating body in one second is (a) frequency (b) noise (c) loudness (d) pitch

Question 13. The maximum displacement of a body from its mean position is called (a) amplitude (b) oscillation (c) periodic motion (d) frequency

Question 14. Sound usually travels through which medium to reach our ears? (a) Air (b) Water (c) Wood (d) Asbestos

Question 15. 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

Question 16. What is the speed of sound in air? (a) 110 m/s (b) 220 m/s (c) 330 m/s (d) 440 m/s

Question 17. 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.

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

Question 19. The voice box is also called as (a) pharynx (b) throat (c) larynx (d) windpipe

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

Question 21. 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

Question 22. Cochlea is a part of (a) hearing organ (b) sound producing organ (c) muscular organ (d) air pollution

Question 23. 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)

Question 24. If we tighten the strings of an instrument, pitch will be (a) higher (b) lower (c) constant (d) no pitch

Question 25. Sound having frequency below 20 Hz is called (a) infrasound (b) ultrasound (c) megasound (d) microsound

Question 26. To and fro or back and forth motion of an object is termed as (a) frequency (b) amplitude (c) vibration (d) time period

Question 27. The sound above ……………… is physically painful. (a) 20 dB (b) 40 dB (c) 60 dB (d) 80 dB

Question 28. In dholak, sound is produced due to (a) stretched membrane (b) stretched strings (c) air column (d) none of these

Class 8 Science Chapter 13 Sound

Learning objectives.

• To know about sound and how it is produced.
• To understand the propagation of sound in a medium.
• To learn the types of waves.
• To learn the characteristics of sound.
• To learn the terms related to sound waves – Amplitude, frequency, time period.
• To know the frequency range of hearing in humans.
• To learn about noise pollution and measurements to limit noise pollution.

Importance of Practicing MCQ Questions for Class 8 Science

Solving MCQs can be an effective way for class 8 science students to understand concepts better. Here are some ways in which solving MCQs can help students understand science concepts:

• Encourages active learning:  MCQs require students to actively engage with the material and think critically about the concepts they are studying. Rather than simply memorizing information, students must analyze the options presented and choose the most appropriate answer. This helps to reinforce the material in their minds and encourage active learning.
• Provides immediate feedback:  MCQs provide immediate feedback to students. When students answer a question incorrectly, they can learn from their mistakes and identify areas where they may need additional support. This feedback is crucial for helping students to identify gaps in their understanding and make corrections quickly.
• Promotes retention of information:  MCQs can also help students retain information more effectively. By repeatedly reviewing and answering questions about a particular concept, students can reinforce their understanding of the material and commit it to memory more easily.
• Helps students to organize their knowledge:  When students are presented with a series of MCQs on a particular topic, they must organize their knowledge of the subject and identify the most important information. This process helps them to develop a deeper understanding of the material and strengthens their ability to recall key facts and concepts.
• Improves test-taking skills:  Finally, solving MCQs can help students develop better test-taking skills. By practicing MCQs, students can learn how to eliminate incorrect answer choices, manage their time effectively, and avoid common mistakes that can cost them points on tests and exams.

Frequently Asked Questions (FAQs)

Ans. Sound is a form of energy which produces a sensation of hearing in our ears.

Ans. Sound is produced by the vibration of an object. The vibrating object vibrates the particles of air surrounding it. This creates a disturbance which is passed to the adjacent particles and the process continues. This is how a sound wave is generated. Sound waves are not visible. Sound waves reach our eardrum and make it vibrate. (Eardrum is like a stretched rubber sheet). The eardrum sends vibrations to the inner brain. From there, the signal goes to the brain. This is how we hear.

Ans. A sound wave is a periodic disturbance which requires a material medium for its propagation.

Ans. The medium must possess the following properties for the propagation of waves.

• The medium should be able to return to its original position after being disturbed, i.e., the medium must possess elasticity.
• The medium must be capable of storing energy i.e., the medium must have inertia.

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• NCERT Exemplar
• NCERT 8 Science Exemplar
• Chapter 13: Sound

NCERT Exemplar Class 8 Science Solutions for Chapter 13 - Sound

Ncert exemplar solutions class 8 science chapter 13 – free pdf download.

NCERT Exemplar Solutions for Class 8 Science Chapter 13 Sound is a crucial study material for students studying in CBSE Class 8. This exemplar has answers to the questions provided in NCERT Exemplar. By solving NCERT Exemplar Solutions , students will gain all the important skills required to boost their problem-solving capacity. These Exemplar solutions have different kinds of questions such as MCQs, very short answer questions, short answer questions, long answer questions and numerical problems. The exemplar solutions for Class 8 Science Chapter 13 Sound has answers to 10 MCQs, 5 very short questions, 5 short answer questions and 5 long answer questions.

In this chapter, students will learn how sound is produced by a vibrating body, sound produced by humans, and how sound propagates through air and water. Solving the NCERT Exemplar Solutions Class 8 Science Chapter 13 Sound will help the students to understand the higher-order thinking questions as well as to score good marks in the annual exam. To download the NCERT Exemplar questions visit the below downloadable link.

Download the PDF of NCERT Exemplar Class 8 Science Solutions for Chapter 13 – Sound

Access Answers to NCERT Exemplar Solutions Class 8 Science Chapter 13 – Sound

Multiple-choice questions.

1. A list of mediums is given below.

(iv) vacuum

In which of these mediums can sound travel?

(a) i & ii only

(b) i, ii & iii only

(c) iii & iv only

(d) ii, iii & iv only

Answer is (b) i, ii & iii only

Explanation:

Sound requires a medium to travel. In a vacuum, there is no medium to transmit sound waves hence sound cannot travel in a vacuum.

2. The loudness of a sound depends on:

(a) its amplitude.

(b) its frequency.

(c) its time period.

(d) its speed.

Answer is (a) its amplitude.

Loudness is directly proportional to the amplitude of sound waves. If the amplitude is high then the sound will be louder and the sound will be feeble if the amplitude is low.

3. Which of the following statements is correct?

(i) Sound is produced by vibrations.

(ii) Sound requires a medium for propagation.

(iii) Light and sound both require a medium for propagation.

(iv) Sound travels slower than light.

(c) ii, iii & iv only

(d) i, ii & iv only

Answer is (d) i, ii & iv only

Statement iii) is wrong because light and sound are two different entities.

4. An object is vibrating at 50 hertz. What is its time period?

Answer is (a) 0.02 s

If an object is vibrating at 50 hertz

Its time period will be 0.02 sec

5. In order to reduce the loudness of a sound, we have to

(a) decrease its frequency of vibration of the sound.

(b) increase its frequency of vibration of the sound.

(c) decrease its amplitude of vibration of the sound.

(d) increase its amplitude of vibration of the sound.

Answer is (c) decrease its amplitude of vibration of the sound.

Sound is directly proportional to the loudness of sound. Hence by decreasing amplitude loudness of the sound decreases.

6. The loudness of sound is measured in units of

(a) Decibel (dB)

(b) Hertz (Hz)

(c) Metre (m)

(d) Metre/Second (m/s)

Answer is (a) Decibel (dB)

7. The loudness of sound is determined by the

(a) amplitude of vibration

(b) the ratio of amplitude and frequency of vibration

(c) frequency of vibration

(d) product of amplitude and frequency of vibration

Answer is (a) amplitude of vibration

Loudness is directly proportional to the amplitude of sound waves. If the amplitude is high, then the sound will be louder and the sound will be feeble if the amplitude is low.

8. 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 is (c) 60 vibrations per minute

1Hz= 1 vibration/second

1 minute=60 seconds hence 1 hertz = 60 vibrations /minute

9. Pitch of sound is determined by its

(a) frequency

(b) amplitude

(d) loudness

Answer is (a) frequency

10. Ultrasound has a frequency of vibration

(a) between 20 and 20,000 Hz

(b) below 20 Hz

(c) above 20,000 Hz

(d) between 500 and 10,000 Hz

Answer is (c) above 20,000 Hz

Very Short Answer Questions

11. Lightning can be seen as the moment it occurs. Paheli observes lightning in her area. She hears the sound 5 s after she observed lightning. How far is she from the place where lightning occurs? (speed of sound = 330 m/s).

Distance=330ms x 5s

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

Larynx or vocal cords vibrate when we speak.

13. Boojho saw a cracker burst at night at a distance from his house. He heard the sound of the cracker a little later after seeing the cracker burst. Give the reason for the delay in hearing the sound.

Speed of light is faster than the speed of sound, hence Boojho heard the sound of the cracker a little later after seeing the cracker burst.

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

When we hear a sound our eardrum vibrates.

15. Name two musical instruments which produce sound by vibrating strings?

Sitar and Veena

Short Answer Questions

16. A simple pendulum makes 10 oscillations in 20 seconds. What is the time period and frequency of its oscillation?

Time period: 2 s

frequency : 0.5 oscillations/sec

A pendulum makes 10 oscillations in 20 seconds.

So it makes 1 oscillation in \(\begin{array}{l}\frac{20}{10}\end{array} \) sec = 2sec

Time period=2 sec

Frequency= \(\begin{array}{l}\frac{1}{t}\end{array} \) = \(\begin{array}{l}\frac{1}{2}\end{array} \) = 0.5 Hz

17. We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us?

Everybody has its own range of frequency. But we can only hear frequencies in the range of 20hz to 2000 Hz so we cannot hear the sound of a few vibrating bodies.

18. Suppose a stick is struck against a frying pan in a vacuum. Will the frying pan vibrate? Will we be able to hear the sound? Explain.

The frying pan will vibrate. We will not be able to hear the sound of vibration because sound cannot travel in a vacuum.

19. Two astronauts are floating close to each other in space. Can they talk to each other without using any special device? Give reasons.

In space there will be no medium for sound waves to travel and it will be the vacuum. Sound cannot travel in vacuum hence sound cannot be heard without any special device.

20. List three sources of noise pollution in your locality.

Industrial sirens, Vehicle honking and bursting crackers.

Long Answer Questions

21. We have a stringed musical instrument. The string is plucked in the middle first with a force of greater magnitude and then with a force of smaller magnitude. In which case would the instrument produce a louder sound?

The amplitude of vibration determines the loudness of the sound. When a string is plucked with greater force amplitude of string will be larger. This makes the sound louder.

22. How is the sound produced and how is it transmitted and heard by us?

Sound is produced when the body starts vibrating by any force. This vibration produces waves which travel through a medium to reach the destination(Our ear) where it will be heard.

We hear the sound by our ears. The shape of the outer part of the ear is like a funnel. When sound enters it, it travels down a canal at the end of which there is a thin stretched membrane. 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.

23. An alarm bell is kept inside a vessel as shown in Fig. 13.1. A person standing close to it can distinctly hear the sound of the alarm. Now if the air inside the vessel is removed completely how will the loudness of alarm get affected for the same person?

Air needs a medium to get transmitted. If we slowly remove the air inside the bottle. Sound will not be having medium to travel as it will be the vacuum. Due to vacuum loudness of the sound decrease gradually with the quantity of the air in the bottle.

24. The town hall building is situated close to Boojho’s house. There is a clock on the top of the town hall building which rings the bell every hour. Boojho has noticed that the sound of the clock appears to be much clearer at night. Explain.

• When sound is initiated, speed, pitch, and loudness are all initiated with vibration. During the daytime, there is a number of vibrations around us. This results in a decrease of the amplitude of vibrations. During the night, there will be no such disturbances which will make the sound clearer.

25. Suggest three measures to limit noise pollution in your locality.

i) Trees must be planted along the roads and around the buildings.

ii) Use of horns should be minimised.

iii) Silencers must be installed in transport vehicles and industrial machines.

Important Topics Covered in NCERT Exemplar Solutions for Class 8 Science Chapter 13 Sound

• Sound is Produced by a Vibrating Body
• Sound Produced by Humans
• Sound Needs a Medium of Propagation
• We Hear Sound through Our Ears
• Amplitude, Time Period and Frequency of a Vibration
• Audible and Inaudible Sounds
• Noise and Music
• Noise Pollution

Students are suggested to visit the BYJU’S website to access the latest NCERT Solutions , NCERT Exemplar, notes, sample papers and previous years’ question papers for Classes 6 to 12 and get full assistance for the annual exam. They can also download BYJU’S – The Learning App to study using interactive and engaging videos.

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

What are the topics and subtopics present in chapter 13 of ncert exemplar solutions for class 8 science, how can i score full marks in chapter 13 of ncert exemplar solutions for class 8 science, how is sound produced covered in chapter 13 of ncert exemplar solutions for class 8 science.

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• Rational Numbers Class 7 Case Study Questions Maths Chapter 8

Last Updated on September 6, 2024 by XAM CONTENT

Hello students, we are providing case study questions for class 7 maths. Case study questions are the new question format that is introduced in CBSE board. The resources for case study questions are very less. So, to help students we have created chapterwise case study questions for class 7 maths. In this article, you will find case study questions for CBSE Class 7 Maths Chapter 8 Rational Numbers. It is a part of Case Study Questions for CBSE Class 7 Maths Series.

Table of Contents

Case Study Questions on Rational Numbers

Class VII students were asked to compare numbers. The numbers were $\frac{-14}{9}$ and -1.05. How did the student compare as there are two methods to compare. Which one did he find easier?

Difficulty Level: Medium

Q. 1. Convert – 1.05 into fraction (a) $\frac{-21}{2}$ (b) $\frac{-21}{20}$ (c) $\frac{-21}{200}$ (d) $\frac{-21}{2000}$

Ans. Option (b) is correct. Explanation:

$$ \begin{aligned} -1.05 & =\frac{-105}{100} \\ & =\frac{-21}{20} \end{aligned} $$

Q. 2. Which is greater $\frac{-14}{9}$ or $\frac{-21}{20}$ ? (a) $\frac{-14}{9}$ (b) $\frac{-21}{20}$ (c) Both are equal (d) None of these

Ans. Option (b) is correct. Explanation: $\frac{-14}{9}$ or $\frac{-21}{20} \quad$ (L.C.M. of 9, 20 is 180)

$$ \begin{aligned} & =\frac{-280<-189}{180} \\ & =\frac{-14}{9}<\frac{-21}{20} \end{aligned} $$

Q. 3. Out of $\frac{-14}{9}, \frac{-21}{20}, \frac{-7}{8}$ and $\frac{-21}{25}$ which is a nonterminating decimal ? (a) $\frac{-21}{20}$ (b) $\frac{-21}{25}$ (c) $\frac{-14}{9}$ (d) $\frac{-7}{8}$ Ans. Option (c) is correct. Explanation: $\frac{-14}{9}$;

$$ \begin{gathered} 9) \overline{14(1.555} \\ \frac{9}{50} \\ \frac{45}{50} \\ \frac{45}{50} \\ \frac{45}{5} \\ \frac{-14}{9}=1.55=1 . \overline{5} \end{gathered} $$

It is a non-terminating decimal.

Q. 4. Divide $-1 \frac{1}{55} \div-5 \frac{8}{11}$

Sol. $-1 \frac{1}{55} \div-5 \frac{8}{11}$

$$ \begin{aligned} & =\frac{-56}{55} \div \frac{-63}{11} \\ & =\frac{-56}{55} \times \frac{11}{-63} \\ & =\frac{8}{45} \end{aligned} $$

Q. 5. Simplify: $2+\frac{1}{3}+\frac{1}{-5}$ (Medium) Sol. $2+\frac{1}{3}+\frac{1}{-5}$

$$ \begin{aligned} & =\frac{2}{1}+\frac{1}{3}-\frac{1}{5} \\ & =\frac{30+5-3}{15} \\ & =\frac{32}{15} \end{aligned} $$

• Visualizing Solid Shapes Class 7 Case Study Questions Maths Chapter 13
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Fractions and Decimals Class 7 Case Study Questions Maths Chapter 2

Integers class 7 case study questions maths chapter 1, topics from which case study questions may be asked.

• Rational Numbers
• Rational Numbers on a Number Line
• Rational Numbers in Standard Form
• Comparison of Rational Numbers
• Rational Numbers between Two
• Operations on Rational Numbers

Every rational number except zero has its reciprocal. Every rational number can be represented in decimal form. Addition, subtraction, multiplication, division is same as fractional numbers but following the rules of integers.

Case study questions from the above given topic may be asked.

Every natural number is a rational number but every rational number is not a natural number. Addition of two rational numbers is a rational number . Subtraction of two rational numbers is a rational number. Product of two rational numbers is a rational number. Division of two rational numbers is a rational number.

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Frequently Asked Questions (FAQs) on Rational Numbers Case Study

Q1: what are rational numbers.

A1: Rational numbers are defined as numbers that can be expressed in the form  p/q ​, where  p  and  q  are integers and q≠0.

Q2: What is the difference between integers and rational numbers?

A2: All integers are rational numbers because they can be written in the form of p/1 where, p is an integer. However, not all rational numbers are integers. For example, 1/2​ is a rational number but not an integer.

Q3: How do you compare two rational numbers?

A3: To compare two rational numbers, you need to express them with the same denominator. Once the denominators are the same, compare the numerators to determine which number is greater or smaller.

Q4: How are rational numbers represented on the number line?

A4: Rational numbers can be represented on the number line by converting them into decimal or fractional form. Positive rational numbers are placed to the right of zero, and negative rational numbers are placed to the left of zero.

Q5: What is the additive inverse of a rational number?

A5: The additive inverse of a rational number p/q​ is −p/q. When a rational number is added to its additive inverse, the result is zero.

Q6: Can zero be a rational number?

A6: Yes, zero is a rational number because it can be expressed as 0/1​, which fits the definition of a rational number.

Q7: How do you add or subtract rational numbers?

A7: To add or subtract rational numbers, first convert them to have a common denominator. Then add or subtract the numerators while keeping the denominator the same.

Q8: How do you multiply two rational numbers?

A8: To multiply two rational numbers, simply multiply the numerators together and the denominators together

Q9: Are there any online resources or tools available for practicing rational numbers case study questions?

A9: We provide case study questions for CBSE Class 7 Maths on our  website . Students can visit the website and practice sufficient case study questions and prepare for their exams. If you need more case study questions, then you can visit Physics Gurukul website. they are having a large collection of case study questions for all classes.

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