Sound Question Answers: NCERT Class 8 Science

Welcome to the Chapter 13 - Sound, Class 8 Science - NCERT Solutions page. Here, we provide detailed question answers for Chapter 13 - Sound.The page is designed to help students gain a thorough understanding of the concepts related to natural resources, their classification, and sustainable development.

Our solutions explain each answer in a simple and comprehensive way, making it easier for students to grasp key topics and excel in their exams. By going through these Sound question answers, you can strengthen your foundation and improve your performance in Class 8 Science. Whether you're revising or preparing for tests, this chapter-wise guide will serve as an invaluable resource.

Vibrating objects produce sound.
In humans sound is produced by vibration of the vocal cords.
Sound cannot travel in vacuum.
Sound can travel through a solid, liquid or a gas medium as well.
The vibration of sound are senses by the eardrum.
Eardrum is a stretched membrane.
Eardrum send signals to brain. This process is known as hearing.
Frequency of oscillation may be defined as the number of oscillation or vibrations in one second.
Hertz (Hz) is the unit of frequency.
The unpleasant and unwanted sound is called as noise. It may lead to noise pollution.
Many health hazards are produced by noise pollution.
Loudness of sound is called as amplitude or we can say the displacement of vibrating object from its main position is called amplitude.
Eardrum is a stretched membrane which separates the middle ear from the outer ear which vibrated to produce sound.
Larynx is known as the voice box which produces sound.
Loudness is the characteristics of sound which depends upon the amplitude.
Oscillation is the complete to and fro motion of an object about at its mean position.
Pitch is known as the flatness or shrillness of a sound.
Time period may be defined as the time taken by vibrating objects to complete one oscillation.
Vibration is the to and fro movement of a body.
Windpipe connects the larynx to the lungs, it is tube like structure of respiratory tract.

Download PDF - Chapter 13 Sound - Class 8 Science

Download PDF - NCERT Examplar Solutions - Chapter 13 Sound - Class 8 Science

Exercise 1 ( Page No. : 171 )

Q1	Choose the correct answer : Sound can travel through (a) gases only (b) solids only (c) liquids only (d) solids, liquids and gases.
Ans:	(d) Solid, liquids and gases Sound can travel through solid, liquid as well as through gas medium. Sound cannot travel in vacuum.

Q2	Which of the following voices is likely to have minimum frequency? (a) Baby girl (b) Baby boy (c) A man (d) A woman
Ans:	(a) Baby girl A baby girl voice is likely to have less or minimum frequency in comparison to baby boy, a man and a woman. A baby girl produced a low pitch sound.

Q3	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)
Ans:	(a) True This statement is true because sound cannot travel in vacuum. Sound is produced by vibrations. If there, air is not present then sound cannot be produced. (b) False This statement is false because the number of oscillations per second of a vibrating object is called its frequency. (c) False This statement is false if the amplitude of vibration is large, then the sound will be sharp and having a high pitch. (d) True This statement is true because the range of hearing a sound is 20 Hz to 20000 Hz. Above 20,000 Hz the sound is not audible and harmful for ears. (e) False This statement is false because as higher is the frequency, the pitch of the sound is high. (f) False This statement is false because the unwanted and unpleasant sound is termed as noise pollution whereas the pleasant sound is known as music. (g) True This statement is true because noise pollution is harmful to the ears and it may cause partial hearing impairment. The unwanted and unpleasant sound is known as noise pollution.

Q4	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.
Ans:	(a) Time period Time period may be defined as the time taken by an object or a body to complete the one oscillation or a cycle. (b) Amplitude Amplitude shows the loudness of the sound. When the amplitude of the vibration is larger, then the sound produced will be very loud. When the amplitude is small then the produced sound will be feeble. (c) Hz Hertz is the unit of frequency. Frequency may be defined as the number of oscillation in one second. (d) Noise The sound which is unpleasant and unwanted to ears known as noise whereas the sound which us pleasant to the ears is known as music. (e) Pitch If the frequency of the vibration is higher, then the produced sound will be shrill and it has high pitch whereas if the frequency of vibration is lower, then the sound will contain lower pitch.

Q5	A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Ans:	Number of oscillations of pendulum = 40 Time taken = 4 second Frequency = Number of oscillation Time taken Frequency = 40/4 = 10 Hz

Q6	The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
Ans:	Number of vibrations of mosquito wings in one second = 500 Frequency = 500 Hz Time period = 1 Frequency = 1/500 = 0.02 second

Q7	Identify the part which vibrates to produce sound in the following instruments: (a) Dholak (b) Sitar (c) Flute
Ans:	Dholak: In Dholak, when stretched membrane vibrates, then it produces sound. The stretched membrane is beaten up for vibrations, then it produces sound. Sitar: In Sitar, vibrations are produced by the stretched string. When the strings are pulled or we can say pushed, then production of vibrations occurs and then it produces pleasant sound. Flute: In Flute, vibrations are produced by the air columns. In this, a number of holes are present, through them air produces sound. It produced a pleasant sound.

Q8	What is the difference between noise and music? Can music become noise sometimes?
Ans:	The sound which is unpleasant or unwanted to ears are known as noise whereas the sound which is pleasant to our ears known as music. Music gives us relaxation whereas noise produces so many health problems like loss of hearing, headache and many other problems. Yes, music can become a noise sometime when the instrument like Dholak produces a very high volume of sound.

Q9	List sources of noise pollution in your surroundings.
Ans:	There are many sources of noise pollution around us. Some are as follows: Sound produced by vehicles. Sound of a loud speaker Sound of bog machines in factories. Sound produced at construction sites. Sound produced by television at high volume. Bursting of crackers produces noise pollution and air pollution too.

Q10	Explain in what way noise pollution is harmful to humans.
Ans:	The unpleasant or unwanted sound is called as noise. Noise pollution is harmful for the human beings. Some of the health hazards produced by the noise pollution are as follows: Lack of sleep Hypertension Anxiety Headache Loss of hearing etc.

Q11	Your parents are going to buy a house. They have been offered one on the roadside and another three lanes away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Ans:	I would suggest my parents to buy the house which is three lanes away from the roadsides. It will protect us from the noise pollution. The house should bought away from roads in a peaceful place which gives positive energy and keeps you calm.

Q12	Sketch larynx and explain its function in your own words.
Ans:	Larynx is also known as the voice box. The sound is produced by the larynx. It feels like a hard bump on touch that seems to move when you swallow. This is also known as the voice box.

Q13	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?
Ans:	In the sky, lightning and thunder takes place at the same time and at the same distance from us. Lightning is seen earlier and then thunder is heard later because the speed of the light is very large in comparison to the speed of sound in air. Speed of light = 3ooooo km/s Speed of sound in air = 330 m/s air