This document contains a chapter on sound from a 7th standard textbook. It includes 17 questions and answers about the basics of sound. Key points covered include:
1) Sound is produced by vibrations of an object. An object must vibrate to produce sound.
2) Sound travels through air, which is a gas, to reach our ears, such as the sound of a ringing telephone bell.
3) Vocal cords in the voice box vibrate when we speak, producing sound. Air from the lungs makes the vocal cords vibrate.
4) The pitch of men's, women's, and children's voices differs due to differences in the pitch, which depends on the vibration frequency.
This document contains a chapter on sound from a 7th standard textbook. It includes 17 questions and answers about the basics of sound. Key points covered include:
1) Sound is produced by vibrations of an object. An object must vibrate to produce sound.
2) Sound travels through air, which is a gas, to reach our ears, such as the sound of a ringing telephone bell.
3) Vocal cords in the voice box vibrate when we speak, producing sound. Air from the lungs makes the vocal cords vibrate.
4) The pitch of men's, women's, and children's voices differs due to differences in the pitch, which depends on the vibration frequency.
This document contains a chapter on sound from a 7th standard textbook. It includes 17 questions and answers about the basics of sound. Key points covered include:
1) Sound is produced by vibrations of an object. An object must vibrate to produce sound.
2) Sound travels through air, which is a gas, to reach our ears, such as the sound of a ringing telephone bell.
3) Vocal cords in the voice box vibrate when we speak, producing sound. Air from the lungs makes the vocal cords vibrate.
4) The pitch of men's, women's, and children's voices differs due to differences in the pitch, which depends on the vibration frequency.
This document contains a chapter on sound from a 7th standard textbook. It includes 17 questions and answers about the basics of sound. Key points covered include:
1) Sound is produced by vibrations of an object. An object must vibrate to produce sound.
2) Sound travels through air, which is a gas, to reach our ears, such as the sound of a ringing telephone bell.
3) Vocal cords in the voice box vibrate when we speak, producing sound. Air from the lungs makes the vocal cords vibrate.
4) The pitch of men's, women's, and children's voices differs due to differences in the pitch, which depends on the vibration frequency.
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Chapter – 6(Physics)
Sound Std-7 Answer the following questions 1.How is sound produced? Ans: Sound is produced by the vibrations of an object. 2.What should an object do to produce sound? Ans:An object should vibrate to produce sound. 3.What brings the sound of a ringing telephone bell to our ears? Ans: Sound of ringing telephone bell travels to us through the air in the room which is a gas. 4.(a)What is the name of the strings in the human voice box which vibrate to produce sound? Ans: vocal cords in our voice box vibrate rapidly when we speak ,to produce sound. (b) What makes this strings vibrate? Ans:When we talk ,air from the lungs passes up the wind pipe .This air makes the vocal cords in our voice box to vibrate rapidly.And vibrating vocal cords produce the sound. 5.why are the voices of men ,women and children different? Ans: Pitch is that characteristic of sound by which we can distinguish between different Sounds of the same loudness.we can differentiate the voice as they differ in their Pitch. 6.If you want to hear a train approaching from far away ,why is it more convenient to Put the ear to the track? Ans: If a train is very far away from us,we cannot hear the sound of approaching train through the air.But if we put our ear to the railway line made of steel ,then we can hear the sound of the coming train easily even if it is quite far away.This is due to the fact that sound travels much more faster through the railway line made of steel than through air. 7.What is meant by the (a)Loudness (b)Pitch and (c)Sound Quality or Timbre of sound Ans(a)Loudness: it is that characteristic property of sound which is direct to the square of amplitude of vibrations .The loudness of sound expressed in the unit called decidel .(db) (b)Pitch : Pitch is the shrillness or flatness of the sound which depends upon the Frequency .The pitch of a sound is directly proportional to its frequency. (c) Quality or Timbre of sound: quality is that characteristic of sound which enables us to distinguish between the sounds produced by different sound Producing objects even if they are of the same loudness and pitch. 8.(a)What is vibration (or an oscillation)Define ‘ampitude’,frequency and Time-period of vibration of an object.
Ans: Vibration is one complete to and fro movement
of the pendulum bob in one vibration or oscillation. Amplitude: The maximum distance to which the bob of a vibrating pendulum goes from its central position is called amplitude of vibrations. Frequency: The number of vibrations made per second by a vibrating body is called the frequency of vibrations .The unit of frequency of vibration is hertz. Time-period: The time taken by pendulum bob to complete one vibration is called the time-period of pendulum. 9.Write the relationship between frequency and time period Ans: Time-period is the time required to make 1 vibration and frequency is the number Of vibrations made in 1 second This means that time-period is equal to the reciprocal of frequency. Time-period =1/frequency 10.What are longitudinal waves? Ans: Particles of the medium through which the sound travels ,vibrate parallel to the direction that the sound wave moves .Such a type of wave is called longitudinal wave. 11.What is rarefaction and compression with reference to longitudinal wave? Ans: Rarefaction: When the air molecules expand into a large region of space .This is known as rarefaction. Compression: When air molecules compress into a small region of space is known as compression. 12.Explain compression and rarefaction with a diagram Ans:Fig 6.6 page 108 13. How can the pitch of sound produced in a piano be changed? Ans: Pitch of sound produced in a piano can be changed by changing the frequency . 14.Write the approximate speed of sound in (a)air , (b)water and (c)steel Ans:speed of sound in air is 340 m/s Speed of sound in water is 1500 m/s Speed of sound in steel is 5000 m/s
15.During a thunderstorm ,the sound of thunder is
heard after the lightning is seen Why? Ans: It is due to the very high speed of light that we see the flash of lightning first and It is due to comparatively low speed of sound that the thunder is heard a little later. 16.Explain sound needs a medium for propagation Ans: The substance through which sound travels is called medium. Sound can travel through soids ,liquids and gases because the molecules of solids ,liquids and gases carry sound waves from one place to another. Sound cannot travel through vacuum because vacuum has no molecules which can vibrate and carry sound waves. So a material medium like air, water ,wood etc, is necessary for the transmission of sound from the source of sound to our ears. 17.How is loudness of sound affected when amplitude of vibrations is doubled and when it is halved? Ans: If the amplitude of vibrations is doubled ,then the loudness will become four times And if the amplitude of vibrations is halved ,then the loudness will become one-fourth.
