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GURUKUL CENTRAL ACADMY, CH.- 13 - sound, WORKSHEET-1, Refer text book, WORKSHEET-2, A. 1. energy 2. vibrates 3. compression 4. rarefaction, 5. wave 6. medium 7. vacuum 8. frequency 9. pitch, 10. flat, 11. echo 12. echolocation, B. Refer text book, , TEXTBOOK EXERCISES, Page 148 Try These, 1. vibrations 2. vacuum 3. source of sound, 4. 20 Hz to 20,000 Hz 5. Pitch, 6. middle ear, Page 152 Try These, 1. T 2. F 3. F 4. T 5. F, , EXERCISES, A. 1. b. 2. d. 3. b. 4. a. 5. a. 6. c. 7. a. 8. d. 9. b. 10. d., B. 1. to and fro, 3. shrillness, 6. energy, , 2. compression, rarefaction, 4. greater 5. outer, 7. wind, 8. infrasonic

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GURUKUL CENTRAL ACADMY, C. 1. – d., D. 1. T, E., , 2. T, , 3. – e., , 4. – f., , 3. F 4. T 5. F, , 5. – a., , 6. – b., , 6. T 7. F 8. T 9. F, , 1. The number of vibrations produced per second is called, frequency., 2., , 3., , 4., , 5., , 6., , F., , 2. – c., , The maximum displacement of a vibrating body from its, mean position is called amplitude., Sound is a form of energy that produces the sensation of, hearing., The property of a sound that is determined by the, frequency of the waves producing it is called pitch., The presence of excessive and unwanted noise in the, environment is called noise pollution., The sound heard after reflection from a distant surface is, called echo., , 1. Music: If a sound is produced with regular vibrations and, it is pleasing to the ear it is called music., Noise: If sound consists of irregular vibrations and it is, unpleasing to ears it is called noise.

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GURUKUL CENTRAL ACADMY, 2., , 3., , G., , Ultrasonic: Frequency range which is higher than the sonic, range is called ultrasonic., Infrasonic: Low frequency sounds which we cannot hear is, called infrasonic., Stringed Instrument:, 1. In stringed instrument sound is produced by vibrating, strings., 2. Guitar, violin, sitar etc. are stringed instruments., Wind instrument:, 1. In wind instrument sound is produced by the vibrations, produced in the air column inside these instruments., 2. Flute, shehnai, clarinet etc. are wind instruments., , 1. Amplitude of the vibration, 2. Steel, 3. Decibel, 4. Hard, 5. Pinna and ear tube, 6. Hammer, anvil and stirrup, 7. Hertz (Hz), 8.Whales and bats, 9. Unwanted and unpleasant, 10. Rising number of automobiles and loud speakers, 11. Larynx, 12. Syrinx

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GURUKUL CENTRAL ACADMY, H., , 1. Sound is produced by the to and fro movements of a, vibrating body., 2., , 3., , 4., , 5., , 6., , 7., , 8., , Vibration is the rapid to and fro movement of a body about, a central position., Frequency determines the pitch of the sound. Pitch is extent, of shrillness of sound. Higher the frequency, higher is the, pitch of sound. This indicates that the sound is shrill or very, sharp., The pitch is highest in the bowl with the maximum amount, of water, and lowest in the bowl with the least amount of, water., It produces shriller sounds., The time taken to complete one vibration is called time, period of a vibrating object., Because their vocal cords are shorter., • Echoes are used by doctors to get a picture of organs of, the body. Ultrasonic vibrations reflected by different parts, of an organ help to create an image of the organ.

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GURUKUL CENTRAL ACADMY, •, , 9., , Echoes are used in SONAR (Sound Navigation and, Ranging) to find the depth of the sea and locate under, water objects. Vibrations are sent down from ships. The, principle used here is the fact that the time taken for the, reflected vibrations to return helps one calculate the depth, of the object that reflects the vibrations. This principle is, also used to calculate distances of mountains and, buildings., , • Noise pollution coming from the industries located at a, distance from the city can be reduced by planting trees, close to the industries so that they absorb most of the, noise., • Use of silencers in vehicles reduces the noise coming, from them., • At home radio, television, etc., should be played at lower, volume., , I. 1. Aim: To show that sound cannot travel through vacuum., Procedure:, Take a small alarm clock or any other toy that can produce, sound. Put it in an empty glass jar. You will be able to hear, its sound easily. Now cover the glass jar tightly with a, stopper and connect it with a vacuum pump., Observation:, You will find that as the air starts getting pumped out, the, ticking sound of the clock slowly fades away and finally it

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GURUKUL CENTRAL ACADMY, is not heard at all., This shows that sound needs a medium to travel. It cannot, travel through vacuum., 2., , 3., , Refer page 147., In human beings, sound is produced by the voice box or, larynx. The voice box is situated in the throat at the upper, end of the wind pipe. The sound produced is controlled by, vocal cords, which are thin membranes stretched across the, voice box., , Refer Fig. 13.12., 4., , 5., , Refer Activity 4., The presence of excessive and unwanted noise in the, environment is called noise pollution., Main causes of noise pollution are:, • In offices, there is noise pollution owing to the bells,, telephones, clattering office machines and conversations., On the roads noise pollution occurs due to the rising, number of automobiles each day. Screeching of tyres,, squeaking brakes and sirens at the highest decibels are all, possible factors that add to noise pollution., • Blaring televisions, radios and live shows are other major, factors contributing to noise pollution in India. The other

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GURUKUL CENTRAL ACADMY, most important problem adding to the existing problem of, noise pollution is that the industrial units are not very far, from the inhabited areas or from time to time they are set, up in the residential areas itself., • Air compressors, bulldozers, loaders and, dump trucks are, the major sources of noise pollution at construction sites., Industrial noise adds to noise pollution., 6., , Stringed Instrument:, In stringed instruments such as guitar, violin, sitar, sarangi, and tanpura sound is produced by vibrating strings (metal, wire)., Wind instrument:, Flute, shehnai, clarinet, saxophone, etc., are wind, instruments. Sound in these instruments is produced by the, vibrations produced in the air column inside these, instruments., Percussion instrument:, Dholak, tabla drum, mridangam, etc., are percussion, instruments. They have a membrane stretched over a, cylindrical body of metal, wood or clay. This type of, instrument is played by striking., , 7., , Refer page 147.

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GURUKUL CENTRAL ACADMY, 8., , We can hear the echo of a sound only if it takes 1/10th of a, second to hit the reflecting surface and come back. The, speed of sound in air is about 340 m/s. Therefore, distance, travelled by sound in 1/10th second, = speed time, = 340 m/s (1/10)s = 34 m, Echo can be heard only if the reflecting surface is (34÷2) m,, or about 17 m, away.