Sound ASSIGNMENT 1. Fill in the blank spaces, by choosing the correct words from the list given below : List : loudness, vibrating, music, material, decibel, zero, twenty hertz, reflect, absorb, increases, shrill, high, air, solids (i) Only... bodies produce sound. (ii) Sound needs a... medium for its propagation. (iii) The range of infrasonic vibrations is between... and.... (iv) The pitch of sound in a closed tube... if the length of air column decreases. (v) More the amplitude of a vibrating body, more is its.... (vi) Polished surfaces... sound, but rough surfaces... sound. (vii) High pitched sound is... and has... frequency. (viii) Speed of sound is slowest in... and fastest in... (ix) The loudness of sound is measured in.... (x) The sound which has a pleasant effect on the ears, is called.... 2. Statements given below are incorrect. Write the correct statements. (i) The birds produce sound with the help of vocal chords. (ii) A loud sound increases the concentration and work efficiency. (iii) The time taken by a vibrating body to complete one vibration, is called frequency. (iv) Sound waves travel slower in water as compared to air. (v) The minimum distance between the source of sound and reflecting body should be 71 m, for producing an echo. 3. Write T for true and F for false in front of the following statements : (i) Oiling and greasing of machines, lowers the noise level. (ii) Decibel is the unit of amplitude of sound. 1
(iii) (iv) (v) (vi) The mosquitoes produce sound with the help of syrinx. The range of infrasonic vibrations is less than 20 Hz. The shrill sound can travel through vacuum. With the decrease in frequency, the sound becomes low pitched. (vii) (viii) (ix) (x) For the formation of an echo, the distance between reflecting body and source of sound should be more than 17 m. The maximum displacement of a vibrating particle from one extreme position to another, is called amplitude. All living beings produce sound with vocal chords. The speed of sound in air is 330 m/s. 4. Tick ( ) the most appropriate answer. (i) The characteristics which destinguishes sound from two sources of sound of same loudness and same frequency. (a) pitch (b) loudness (c) timbre (d) periodicity (ii) An echo is produced only, if the distance from the source of sound is : (a) 10 m (b) 15 m (c) 17 m or more (d) 5 m (iii) An instrument used for finding depth of sea, is called : (a) measuring tape (b) diving bell (c) radar (d) sonar (iv) Violin is an example of : (a) wind instrument (b) percussion instrument (c) stringed instrument (d) none of these (v) The speed of sound in air is approximately : (a) 332 ms 1 (b) 33.2 ms 1 (c) 233 ms 1 (d) 2330 ms 1 (vi) The unit of measurement of frequency is : (a) metre (b) second (c) hertz (d) newton (vii) The sound cannot travel through : (a) solid (b) liquid (c) gas (d) vacuum 2
(viii) The sound travels fastest in : (a) air (b) steel (c) water (d) vacuum (ix) A simple instrument used to produce musical sound of fixed frequency in laboratory is : (a) bell (b) tuning fork (c) simple pendulum (d) manometer (x) The loudness of sound is measured in : (a) centimetre (b) joule (c) decibel (d) newton 5. Find the odd one out. Give a reason for your choice. (i) pitch, loudness, timbre, wavelength. (ii) violin, sitar, guitar, drum. (iii) echo, reflection of sound, bats, parrots. (iv) loudspeaker, music system, ear plugs, supersonic plane. 6. (i) How is sound produced? (ii) Describe an experiment in support of your answer in 6(i). 7. A vibrating tuning fork is touched with a freely suspended pith ball as shown in the adjoining diagram. (i) State your observations. (ii) What conclusion would you draw regarding the production of sound from above observations? 8. What do you understand by the following terms as applied to sound? (i) Vibration (ii) Amplitude (iii) Time period (iv) Frequency 9. Derive a relation between time period and frequency of a vibrating body. 3
10. Find the frequency of a wave, whose time period is 0.0008 s. 11. What is the time period of the wave, having a frequency of 400 Hz? 12. 6000 waves of water pass through a point in 10 minutes. Find : (i) Frequency (ii) Time period of water waves 13. (i) Can vibrations of all frequencies produce sensation of sound? (ii) State the range of : (a) Infrasonic vibrations (b) Sonic vibrations (c) Ultrasonic vibrations 14. An electric tuning fork has the time period of 0.00004 s. Find its frequency. By giving a reason, state whether you can hear the above sound or not. 15. (i) State the speed of sound in (a) air (b) steel (c) water (ii) A hammer is struck hard on a railway line. How far will the sound travel in 2.6 s? Assume that the velocity of sound in iron is 5100 m/s. 16. Time in which the sonar fitted on a ship records an echo, is 14.6 s. If the velocity of sound in water is 1600 m/s, find the depth of the sea. 17. The time difference between seeing a flash of gun and hearing its sound is 4.2 s. If the velocity of sound in air is 330 m/s, how far is the gun from the observer? 18. Why did Red Indians put their ear to the ground for detecting enemy movements? 19. Describe an experiment to show that sound cannot travel through vacuum. Draw an appropriate diagram. 20. Explain, why sound cannot reach to us from space. 21. Explain, why is supersonic plane seen first and its sound is heard later. 22. Explain, how can bats locate their prey at night. 23. (i) What do you understand by the term echo? (ii) State two conditions necessary for the formation of an echo. 24. (i) Why are big indoor auditoriums carpeted and their walls made of rough material? (ii) Why can t we hear echoes in small rooms? 4
25. What do you understand by the following terms? (i) Pitch (ii) Loudness 26. A plastic ruler is held against a rotating bicycle wheel whose speed is being gradually decreased. State how does the pitch of sound change and why? 27. Explain the following : (i) Why does the sound of a girl differ from that of a boy? (ii) Why does the sound of violin differ from that of flute? (iii) Why is the sound produced by a drum different, when it is, (a) struck lightly (b) struck strongly? 28. Which part of the following musical instruments vibrate to produce sound? (i) Drum (ii) Sitar (iii) Bagpipes (iv) Tuning fork 29. Name four sources of noise in : (i) Market place (ii) Homes (iii) Garden 30. (i) Name any two stringed instruments. (ii) Name any two wind or reed instruments. (iii) Name any two percussion instruments. 31. State two major differences between noise and musical sound. 32. How do the following produce sound? (i) Human beings (ii) Birds (iii) Insects 33. (i) Name the unit for the measurement of loudness of sound. 5
(ii) Name the source of sound which can produce loudness in the range of : (a) 20 db (b) 60 db (c) 90 db 34. (i) What do you understand by the term noise pollution? (ii) Suggest two ways in minimising noise, in : (a) Homes (b) Surrounding (c) Automobiles 35. State four harmful effects of noise pollution to the workers, working in factories. ANSWERS 10. 1,250 Hz 11. 0.0025 s 12. (i) 10 Hz (ii) 0.1 s 14. 25,000 Hz 15. (ii) 13,260 m 16. 11,680 m 17. 1,386 m 6