Basic Science Solutions for Class 8 Science Chapter 9 Sound are provided here with simple step-by-step explanations. These solutions for Sound are extremely popular among Class 8 students for Science Sound Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Basic Science Book of Class 8 Science Chapter 9 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Basic Science Solutions. All Basic Science Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

Page No 102:

Question A.1:

Answer:

Three characteristics that help us to distinguish one sound from another are loudness, pitch and quality.

Page No 102:

Question A.2:

Three characteristics that help us to distinguish one sound from another are loudness, pitch and quality.

Answer:

Loudness of a sound depends upon the amplitude of the vibrations that produces it.

Page No 102:

Question A.3:

Loudness of a sound depends upon the amplitude of the vibrations that produces it.

Answer:

Pitch of a sound determines how shrill it is. It depends on the frequency of vibrations of the sound.

Page No 102:

Question A.4:

Pitch of a sound determines how shrill it is. It depends on the frequency of vibrations of the sound.

Answer:

When we increase the tautness of the string, sound of large amplitude will be produced. Hence, sound produced will be louder.

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Question A.5:

When we increase the tautness of the string, sound of large amplitude will be produced. Hence, sound produced will be louder.

Answer:

The tautness of the membrane and area of the instrument determine the pitch of the sound produced by a percussion instrument.

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Question A.6:

The tautness of the membrane and area of the instrument determine the pitch of the sound produced by a percussion instrument.

Answer:

Pitch of sound will change when we increase the level of water in the glass.

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Question A.7:

Pitch of sound will change when we increase the level of water in the glass.

Answer:

Sounds of frequency less than 20 Hz are called infrasonics.

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Question A.8:

Sounds of frequency less than 20 Hz are called infrasonics.

Answer:

A dog and a cat are two animals that can hear sounds inaudible to us.

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Question A.9:

A dog and a cat are two animals that can hear sounds inaudible to us.

Answer:

Bats use echoes to locate their prey.

Page No 102:

Question B.1:

Bats use echoes to locate their prey.

Answer:

Multiples of fundamental or basic frequency are called harmonics. They determine the quality of sound. In general, a sound with greater number of harmonics is rich or has a better quality.

Page No 102:

Question B.2:

Multiples of fundamental or basic frequency are called harmonics. They determine the quality of sound. In general, a sound with greater number of harmonics is rich or has a better quality.

Answer:

 

Music Noise
Music is pleasant to ears. Noise is unpleasant to ears.
It is produced by regular vibrations. It is produced by irregular vibrations.

Regular vibrations are those frequencies of vibrations which have a definite relation with each other.

Page No 102:

Question B.3:

 

Music Noise
Music is pleasant to ears. Noise is unpleasant to ears.
It is produced by regular vibrations. It is produced by irregular vibrations.

Regular vibrations are those frequencies of vibrations which have a definite relation with each other.

Answer:

Loudness of sound determines the harmfulness of noise from the point of view of health.
Two major sources of noise pollution are noise produced in factories and on busy streets.

Page No 102:

Question B.4:

Loudness of sound determines the harmfulness of noise from the point of view of health.
Two major sources of noise pollution are noise produced in factories and on busy streets.

Answer:

It is because light travels much faster than sound. Hence, flash light of thunder reaches almost instantly, whereas sound of thunder takes time to reach us.
Loudness of sound determines the distance it can travel before dying out.

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Question B.5:

It is because light travels much faster than sound. Hence, flash light of thunder reaches almost instantly, whereas sound of thunder takes time to reach us.
Loudness of sound determines the distance it can travel before dying out.

Answer:

Larynx is the organ that helps us to speak.
Larynx has two folds of tissues, called vocal cords, that vibrate when the exhaled air is passed through the larynx. These vibrations produce sound.

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Question B.6:

Larynx is the organ that helps us to speak.
Larynx has two folds of tissues, called vocal cords, that vibrate when the exhaled air is passed through the larynx. These vibrations produce sound.

Answer:

Echoes refer to the sounds that are reflected back.
We can hear an echo only if it takes one fifteenth of a second to hit the reflecting surface and come back. It cannot take place all the time; therefore, we do not hear echo all the time.

Page No 102:

Question B.7:

Echoes refer to the sounds that are reflected back.
We can hear an echo only if it takes one fifteenth of a second to hit the reflecting surface and come back. It cannot take place all the time; therefore, we do not hear echo all the time.

Answer:

Doctors use echoes to get a picture of internal organs of the body. Ultrasonic vibrations, reflected by different parts of an organ, help to create an image of the organ. This technology is called echocardiography.

Page No 102:

Question C.1:

Doctors use echoes to get a picture of internal organs of the body. Ultrasonic vibrations, reflected by different parts of an organ, help to create an image of the organ. This technology is called echocardiography.

Answer:

A vibrating body produces sound in the form of energy. This energy is transferred to the particles present in air in all directions. These particles then start vibrating with the same frequency and pass on the vibrations to the neighbouring particles, and so on. This is how sound travels in all directions through air.
In solids, the particles are very close to each other  compared to the particles in air. Hence, sound travels faster through solids than through the air.

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Question C.2:

A vibrating body produces sound in the form of energy. This energy is transferred to the particles present in air in all directions. These particles then start vibrating with the same frequency and pass on the vibrations to the neighbouring particles, and so on. This is how sound travels in all directions through air.
In solids, the particles are very close to each other  compared to the particles in air. Hence, sound travels faster through solids than through the air.

Answer:


Human ear is made of three parts:

  • Outer ear: This is the visible part called pinna. It collects sound waves and directs them to the ear tube. Ear drum lies at the end of this ear tube. When sound strikes, the ear drum vibrates and passes sound to the middle ear.
  • Middle ear: It is a cavity containing three important bones, placed in a manner that they can move with the vibrating ear drum and transmit sound to the inner ear.
  • Inner ear: It contains fluid that vibrates with the transmission of sound and excites tiny hair in it. The hair transforms these vibrations into electrical impulses and these are transmitted to the brain through auditory nerve.

Page No 102:

Question D:


Human ear is made of three parts:

  • Outer ear: This is the visible part called pinna. It collects sound waves and directs them to the ear tube. Ear drum lies at the end of this ear tube. When sound strikes, the ear drum vibrates and passes sound to the middle ear.
  • Middle ear: It is a cavity containing three important bones, placed in a manner that they can move with the vibrating ear drum and transmit sound to the inner ear.
  • Inner ear: It contains fluid that vibrates with the transmission of sound and excites tiny hair in it. The hair transforms these vibrations into electrical impulses and these are transmitted to the brain through auditory nerve.

Answer:

1. The frequency of sound is measured in Hertz
2. The maximum displacement of a vibrating body from its position of rest is its amplitude.
3. The frequency of ultrasonics is higher than the range of human hearing.
4. Sound vibrations die out after travelling some distance due to loss of energy.
5. Sound needs a medium to travel.
6. Industrial noise can be reduced by proper maintenance of machine.
7. The reflecting surface has to be at least 11.3 m away for us to hear an echo distinctly.



Page No 103:

Question E.1:

1. The frequency of sound is measured in Hertz
2. The maximum displacement of a vibrating body from its position of rest is its amplitude.
3. The frequency of ultrasonics is higher than the range of human hearing.
4. Sound vibrations die out after travelling some distance due to loss of energy.
5. Sound needs a medium to travel.
6. Industrial noise can be reduced by proper maintenance of machine.
7. The reflecting surface has to be at least 11.3 m away for us to hear an echo distinctly.

Answer:

(a) Pitch
Pitch of the sound depends on frequency of vibrations.

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Question E.2:

(a) Pitch
Pitch of the sound depends on frequency of vibrations.

Answer:

(c) multiple of frequency of the fundamental
Frequencies of harmonics are multiples of frequency of the fundamental.

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Question E.3:

(c) multiple of frequency of the fundamental
Frequencies of harmonics are multiples of frequency of the fundamental.

Answer:

(d) faster in solids than in air
In solids, the molecules are close to each other. Hence, sound travels faster in solids than in air.

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Question E.4:

(d) faster in solids than in air
In solids, the molecules are close to each other. Hence, sound travels faster in solids than in air.

Answer:

(a) loudness
Decibel is a unit that measures loudness.

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Question E.5:

(a) loudness
Decibel is a unit that measures loudness.

Answer:

(b) are shorter
Women are more high-pitched than men because their vocal cords are shorter.

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Question E.6:

(b) are shorter
Women are more high-pitched than men because their vocal cords are shorter.

Answer:

(b) minimise the reflection of sound
The ceilings of theatres are covered with special materials to minimise the reflection of sound.



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