RBSE Class 8 Science Chapter 10 Sound Solutions

In RBSE Class 8 Science Chapter 10 Sound, students learn about the origin, transmission, loudness, pitch and different types of sound and its uses in our day-to-day lives. Here, we bring you the important questions and solutions of the chapter that will help students to understand all the key concepts and excel in it.

Here’s a simple attempt from our end to cover the chapter-wise explanations of important questions of RBSE Class 8 Science. We hope that students can learn new concepts and benefit from it, while preparing for the RBSE Class 8 2020 exam. All the important questions of the RBSE Class 8 Science Solutions for Chapter 10 Sound have been thoroughly covered and we expect students to absorb knowledge of various concepts in a simpler manner.

In this article, we have extensively covered the important textbook questions and added a few additions with solutions for Chapter 10 from the RBSE Class 8 Science Syllabus. Students can practice from these questions to have a sound knowledge of the chapter, revise it before their exams and score well in this section.

Rajasthan Board Class 8 Science Chapter 10: BYJU’S Important Questions & Answers

RBSE Class 8 Science Chapter 10 Objective Questions: Textbook Important Questions and Solutions

Multiple Choice Questions (MCQs)

Choose the correct answer:

Question 1. In which medium is the transmission of sound not possible?

(a) iron rod

(b) water

(c) air

(d) vacuum

Answer: (d) vacuum

Question 2. The up-down motion around the mean position of an object is called

(a) Vibration

(b) Amplitude

(c) Frequency

(d) Periodic time

Answer: (a) Vibration

Question 3. Speed of sound at 0°C in air is

(a) 350 m/sec

(b) 200 m/sec

(c) 400 m/sec

(d) 331 m/sec

Answer: (d) 331 m/sec

Question 4. Time taken to complete one vibration is called

(a) frequency

(b) time period

(c) amplitude

(d) none of these

Answer: (b) time period

Identify True or False:

In the following statements, tick (T) against those which are true, and (F) against those which are false:

Question 5: Sound generates due to vibration in objects. (True/False)

Answer: True

Question 6: Sound waves do not need medium to transmission. (True/False)

Answer: False

Question 7: Sound has maximum velocity in solids. (True/False)

Answer: True

Question 8: The unit of loudness of sound is decibel (db) (True/False)

Answer: True

Fill in the blanks:

Question 9: The main source of sound in humans is ___________________ .

Answer: Vocal cords

Question 10: The sound waves having frequency more than 20,000 hertz are called ___________________ .

Answer: Ultrasonic Sound

Question 11: The international unit of frequency is ___________________ .

Answer: Hertz

Question 12: The loudness of sound depends on ______________________ .

Answer: Amplitude of vibration

Question 13: The pitch of sound depends on _____________________ .

Answer: Frequency

Short Answer Type Textbook Questions

Question 1: A musical instrument takes 2 seconds to complete 200 oscillations then calculate the frequency of it.

Answer: Given below is the solution –

Frequency = Total number of oscillations / Total time taken

i.e, Frequency = 200 oscillations / 2 sec

= 100 vibration/sec or Hertz.

Question 2: The ringing bell in a temple has frequency 400 vibration/sec, then calculate the periodic time of it.

Answer: Periodic time = 1/ Frequency

i.e, Periodic time = 1/400 vibration per sec

= 0.0025 vibration/sec

Question 3: What are differences in audible, infra-audible, ultra-audible.

Answer: Audible: If the frequency of vibrations is between 20 Hz to 20,000 Hz which can only be heard by us, it is known as audible sound.

Ultra-audible: If the frequency of vibrations is more than 20,000 Hz, it is known as ultra-audible sound.

Infra-audible: If the frequency of sound is less than 20 Hz, then the human ear cannot hear them clearly and such vibrations are called infra-audible vibrations.

Question 4: Define frequency and periodic time. Represent the relation of them by a formula.

Answer: Frequency: The number of oscillations and vibrations per second is known as frequency.

Periodic time: The time taken to complete one oscillation is called periodic time or vibration period.

Given below is the relationship between frequency and periodic time:

Periodic time = 1/ Frequency

Long Answer Type Textbook Questions

Question 5: Draw a human vocal system diagram and explain its working principle.

Answer: The human vocal system is the sound that is produced by the larynx or the voice of the sound box. It is located inside the throat.

Below is the diagram of the human vocal system:

Diagram of the human vocal system

Closed vocal system and Open vocal system

The two vocal fibres are stretched across the larynx or voice box in such a way that it

leaves a narrow slit between them air to pass through. When the lungs force air through the slit, the vocal cords start vibrating, thereby producing sound.

Question 6: What is noise pollution? How does it affect us? How can it be controlled? Explain it in detail.

Answer: The disturbance caused by some irregular sound waves that are produced in the environment by the loud and undesirable sounds from different sources is known as noise pollution.

Noise pollution is comparatively a recent phenomenon which has emerged in the 20th century. This is due to the increasing interdependence of man on different kinds of machines at home, workplace, factories, industries, etc. All this contributes to noise pollution and its adverse effects.

Some of the factors of noise pollution which have an adverse effects in the environment include:

(a) Loudness of sound

(b) Noise duration at a particular place.

Harmful effects of noise pollution: Here are some of the effects of noise pollution in the environment:

1. Noise from the surroundings does have an impact on the speech and discussion among people.

2. Prolonged exposure to noise pollution results in deafness in humans

3. Noise pollution affects work progress and efficiency and impacts our concentration power.

4. Extreme sound causes irritation, anger and affects sleep patterns of individuals.

5. Noise pollution causes headaches and in extreme circumstances may also cause nervous breakdown in people.

Prevention and control measures of noise pollution: Given the current scenario of pollution, it is difficult to eliminate noise completely, but we can definitely lower its level to a certain bearable limit by adopting the following measures:

1. Heavy vehicles should be prohibited from plying in the residential areas roads.

2. Machines should be designed in a manner that produces less noise.

3. All automobiles and generators should include improved silencers.

4. At home, the T.V, radio or music system etc. should be played at a low volume.

5. The factories should be situated away from residential areas.

6. The use of loudspeakers for various religious or social functions should be banned completely.

Question 7: Explain the process of receiving the sound signals to the brain with a labelled diagram of the human ear.

Answer:

Diagram of a human ear

Human ear

The funnel-shaped outer part of the ear is known as the Pinna. It receives the vibrations and sound travels to the ear canal. This is referred to as the hearing cavity. Towards the end of the hearing cavity, a thin membrane gets stretched slightly. This is known as the ear drum and also called tympanum in ordinary language. The vibration of sound passes from the eardrum to the middle ear, which contains three delicate bones – anvil, hammer and stirrup. These bones pass on the vibrations to the inner ear that contains a coiled-like tube called the Cochlea. There are tiny hairs in this tube filled with liquid that picks up vibrations from the middle ear. These send some signal to the brain through the sensory nerves and we are able to hear the sound.

Question 8: How is sound transmitted in solid and gases? Explain it.

Answer: (a) Sound transmission in solid: Take a 1 metre scale, with a 2 metres long metal wire and 2 metres long thread. Now, keep one end of the scale near your end and the other end with your sibling or friend to create sound by lightly rubbing your side of the scale with your nails. However, you can try to repeat the same procedure by stretching and rubbing the metal wire and the thread. You will notice vibrations produced in solids due to scratching at one end and it moves to the other end of the particle. From this experiment, we can analyze how sound travels in solids too.

(a) Sound transmission in gases: Sound reaches our ears due to the transmission of air through vibration. When an object vibrates, then the air nearby also vibrates. Every vibrating particle transmits vibrations to other particles that come into contact with it. Likewise, sound vibrations also reach our ears from one air molecule to another and vibrate our ear drum. These vibrating air molecules collide with our ear drum causing a vibration, that is when we hear the sound.

RBSE Class 8 Science Chapter 10 Additional Questions and Solutions

Short Answer Type Questions

Question 1: What is the number of oscillations executed per second called?

Answer: The number of oscillations executed per second known as frequency. Given below is the formula of frequency:

Frequency = Total number of oscillations / Total time taken

Question 2: What are the three elements of sound?

Answer: The sound that we hear through ears is classified on the basis of three characteristics or elements:

(a) Loudness

(b) Pitch

(c) Quality

Question 3: What is the S.I unit of frequency measured in?

Answer: Hertz (Hz) is the international unit of frequency which measures the total number of oscillations per second.

Question 4: What is the frequency of sound that is less than 20 Hertz called?

Answer: The frequency of sound that is less than 20 Hertz is known as infra-audible sound. Such sounds are used in ‘SONAR’ devices so as to measure the sea depth and the position and speed of a submarine.

Question 5: How do bats fly easily in the dark night sky?

Answer: Some animals such as bats, dogs, etc. can hear ultrasonic sounds. Bats generate ultra-audible sound and can hear the reflecting ultra-audible sound and are able to drive information of any possible danger or obstacle. For this reason, bats can easily fly in the dark night sky.

Question 6: How is sound produced?

Answer: Sound is produced due to the movement of vibrations or oscillations in air. The vibration of the vocal cords also produces sound in human beings.

Question 7: What are the different mediums of sound transmission?

Answer: Sound transmission happens through different mediums such as:

1. Sound transmission in solid

2. Sound transmission in liquid

3. Sound transmission in gas (air)

Question 8: Define Amplitude.

Answer: The maximum displacement of a vibrating object from the mean position is known as the amplitude.

Question 9: What is decibel?

Answer: The loudness of sound is dependent on the amplitude. This implies that with the increase in loudness of sound, there is an increase in the amplitude. The international unit of sound is known as the decibel (dB).

Question 10: Define pitch.

Answer: The characteristics of sharpness (fineness) or thickness (heaviness) of sound is referred to as the pitch. The pitch of sound depends upon the frequency.

Question 11: What is the loudness in decibels for normal breathing in humans?

Answer: 10 decibels is the normal breathing sound in humans. This implies that low pitch sound has low frequency.

Question 12: When is the speed of sound at its lowest?

Answer: The speed of sound at its lowest in the gas (air). It is highest in solid and high in liquid.

Question 13: Why can’t space travellers talk to each other on the moon?

Answer: Two space travellers cannot talk to each other on the moon because there is no air there.

Question 14: Define Oscillation.

Answer: Oscillation is the repetitive variation of an object back and forth in a regular rhythm. It is the way in which an object vibrates to and fro.

Question 15: Can you explain the frequency that a high pitch sound has?

Answer: A high pitch sound usually has high frequency and a low pitch sound has low frequency. With the increase or decrease in the pitch, there is a fluctuation in the frequency of sound.

Question 16: What is the sound that is used in sonography?

Answer: Ultrasonic sounds are used in diagnosing diseases through ultrasonogram. In ordinary words, it is also known as sonography.

Question 17: Define Pinna.

Answer: Pinna is the outer part of the ear which is shaped like a funnel. It is one of the major hearing organs in the human body.

Question 18: What is the purpose of sonography?

Answer: The purpose of sonography is to check the health of the foetus in a pregnant woman’s womb. Some people use it to identify the sex of a child, which is illegal in India.

Question 19: How can we hear sounds?

Answer: Sound always creates vibrations in our ear drum which is then sent to our brain through the hearing cavity by which we feel and hear sound through our ears.

Question 20: Describe noise.

Answer: Noise is the unwanted sound, which may be either categorised as unpleasant, disruptive or loud that impacts our hearing. Noise comprises vibrations that transmit through any medium, such as solid, air or water.

Question 21: Can sound transmit through vacuum?

Answer: Sound cannot transmit in vacuum of space where there are no or very less particles which create vibrations. Hence, sound cannot travel through this medium.

Question 22: What is the full form of SONAR?

Answer: The full form of SONAR is Sound Navigation and Ranging. It is extensively used by submarines to measure the depth of sea and the position and speed of sound.

Question 23: What is an unpleasant sound?

Answer: An unpleasant sound is the loudness of sound which starts from 50 – 80 decibels which is caused by students in a classroom, light vehicles or normal music. Anything that is beyond 80 decibels becomes unbearable to our ears and causes sound pollution in the environment.

Question 24: Why is Indian music considered scientific and melodious?

Answer: Indian music system has seven musical surs – Sa, Re, Ga, Ma, Pa, Dha and Ni collectively called as Sargam, which are purely scientific and melodious. Musicians use these swaras to produce soothing and melodious songs based on sur and taal.

Question 25: Give two uses of ultrasound in medical science.

Answer: Here are two medical uses of ultrasound:

1. It helps in checking the functioning of the internal organs of the body.

2. It is often used to monitor the growth and health of the foetus inside a pregnant woman’s womb.

Question 26: Describe sound transmission in liquids.

Answer: Let’s understand the sound transmission in liquids with the help of an experiment:

Take a bath tub or bucket and fill it with water. Now take 2 – 3 small pieces of pebbles and scratch these with each other inside the bucket. This will create some sound in the water. This shows that it is possible to transmit sound in liquids too.

Question 27: Define embryo death.

Answer: There are some people who try to use sonography as a means to determine the sex of the foetus in a pregnant woman’s womb. After checking if they find the infant child is a girl, they try to destroy the foetus through abortion. This is known as embryo death. Sex determination of an embryo is illegal in India and is a punishable offence under the court of law.

Long Answer Type Questions

Question 28: Distinguish between Noise and musical sound.

Answer: The difference between noise and musical sound is given below:

Noise

Musical Sound

1. It is unpleasant sound to the ears

1. It is pleasant in listening

2. There is frequent fluctuation in the pitch and loudness of sound

2. There is a soothing flow of sound which is melodious to the ears

3. No periodic repetitions of frequency in noise

3. There are repetitions of sounds periodically.

Question 29: Differentiate between Pitch and Loudness of sound.

Answer: Given below is the distinction between pitch and loudness of sound:

Pitch

Loudness of sound

1. Pitch is the frequency of sound effect produced in the brain

1. Loudness of sound is dependent on the amplitude of a vibrating object

2. It is not dependent upon the amount of

energy that is received by the ear

2. It is determined by the amount of energy that is received by the ear in a unit time

3. It changes with the change in the frequency, i.e, high pitch has high frequency and low pitch has low frequency

3. There is no change with the change in frequency

We hope that the above mentioned solutions of “RBSE Class 8 Science Chapter 10 Sound” will help students build a strong foundation of the different concepts mentioned in the chapter.

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