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Tuesday, 30 June 2015

Sound (Questions)

Sound
  1. Sound is a mechanical energy which produces sensation of hearing.
  2. For hearing sound there must be (i) a vibrating body, (ii) a material medium for its propagation and (iii) a receiver, such as human ear.
  3. Sound energy does not propagate through vacuum.
  4. When the particles of a medium oscillate in the same direction, in which wave is being propagated, such a wave is called longitudinal wave.
  5. When the particles of a medium oscillate at right angles to the direction of wave propagation, a transverse wave is produced.
  6. Transverse waves can be produced in solids and liquids, but not in gases.
  7. The highest point on the elevation or hump of a transverse wave is called crest.
  8. The lowest point on the depression or hollow of a transverse wave is called trough.
  9. Compression is a region in a longitudinal wave, where the particles of medium are crowded together. It is a region of high pressure and high density.
  10. Rarefaction is a region in a longitudinal wave, where the particles of medium are spread wide apart. It is a region of low pressure and low density.
  11. The change in density of a medium from maximum value to minimum value and again to maximum value in case of longitudinal wave is called one oscillation.
  12. . The number of compressions and rarefactions (taken together) passing through a point in one second is called frequency. Its unit is hertz.
  13. The time taken by two consecutive compressions or rarefactions to cross a point is called time period.
  14. The magnitude of maximum displacement of a vibrating particle about its mean position is called amplitude.
  15. The pitch of sound is determined by its frequency, i.e., higher the frequency, more is the pitch and hence, shriller is the sound.
  16. The loudness of sound is determined by the amplitude, i.e., more the amplitude, louder is the sound.
  17. The property by virtue of which the note of same pitch and same frequency can be distinguished is called timbre or quality of sound.
  18. Sound travels fastest in solids, slower in liquids and slowest in gases.
  19. A conical tube commonly used for addressing a small group of people is called megaphone.
  20. The phenomenon due to which repetition of sound is heard after reflection from a distant object, after the original sound from a given source dies is called an echo.
  21. For hearing an echo, the minimum distance between the source of sound and reflecting body should be 17m.
  22. Vibrations within the frequency range of 0 Hz to 20 Hz are called infrasonic vibrations. Humans cannot hear them.
  23. Vibrations within the frequency range of 20 Hz to 20000 Hz are called sonic vibrations. They can be heard by humans.
  24. Vibrations above the frequency range of 20,000 Hz known as ultrasonic vibrations. Humans cannot hear them.
  25. A device used to locate depth of sea or submarines, etc, is called sonar.
Sound Assignments in Science Class IX (Term II)


  1. What is reverberation?
  2. . Name the disease that can be caused by UV rays.
  3. If 20 waves are produced per second, what is the frequency in hertz?
  4. What do you understand by the term wave motion?
  5. What do you understand by the term sound energy?
  6. What kind of elastic wave is produced when the particles of a medium vibrate at right angles to the direction of sound propagation?
  7. What kind of wave is produced when the particles of a medium vibrate in the direction of propagation of sound?
  8. The frequency of a sound wave is 32 Hz. What is the time period?
  9. A vibrating wire has a time period 0.025 s, calculate the frequency.
  10. What is the linear distance between a crest and a trough?
  11. The frequency produced by a tuning fork is 41.5 Hz. What is the distance travelled by sound when the tuning fork makes 20 vibrations?
  12. What is the amount of sound energy passing per second through unit area known as?
  13. If a sound wave travels in air and steel with a speed X m/s and Y m/s respectively, find the ratio of the time taken by the sound waves in air and steel to reach a certain point?
  14. Give the relation between wavelenght (λ), velocity (v) and frequency (f).
  15. What is the speed of sound in air at 0 °C?
  16. How are echoes produced?
  17. The frequency of a sound wave in air is 128 Hz. What will be its frequency in water?
  18. A girl hears an echo of her own voice from a distant tall building after 2s. What is the distance of the girl from the building? (Given speed of sound in air = 332 m/s)
  19. A source wave produces 20 compressions and 20 rarefactions in 0.045 seconds. What will be the frequency of the wave?
  20. An elephant can hear a sound of frequency 16 Hz. What is the wavelength of sound in air at this frequency? [Given, speed of sound in air = 320 m/s]
  21. A tuning fork produces 1024 oscillations in 4s. What is the frequency of the tuning fork?
  22. What do you mean by bass in a musical sound?
  23. What kind of waves are used in sonography?
  24. Three persons, A, B and C are made to hear a sound travelling through different mediums as given below : Persons Mediums A Iron Rod B Air C Water Who will hear the sound first? Why?
  25. (i) Define the time period of a wave. (ii) Give the relation among speed of sound v, wavelength l and its frequency v. (iii) A sound wave travels at a speed of 339 ms–1. If its wavelength is 1.5 cm, what is the frequency of the wave?
  26. Draw a neat labelled structure of human ear, depicting the auditory parts only.
  27. A hospital uses an ultrasonic scanner to locate tumours in a tissue. What is the wavelength of sound in a tissue in which the speed of sound is 1.7 km/s. The operating frequency of the scanner is 4.2 MHz (1MHz =106 Hz).
  28. An echo is returned in 6 seconds. What is the distance of reflecting surface from source? [given that speed of sound is 342 m/s.]
  29. 20 waves pass through a point in 2 seconds. If the distance between one crest and adjacent thorough is 1.5 m. Calculate : (a) the frequency (b) the wavelength
  30. What is meant by reverberation of sound? Does reverberation produce undesirable effects in big hall or auditorium? If yes, how are the undesirable effects avoided?
  31. What is echo ranging? State any one application of this technique.
  32. A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. Calculate the time interval between successive compressions from the source? (Speed of sound in air = 330 m/s)
  33. Differentiate between low and high pitch sound using neat and labelled diagram.
  34. (a) Which wave property determines (1) loudness (2) pitch? (b) How are wavelength and frequency related to speed of sound waves?
  35. Define the following : (a) Transverse waves (b) Time period
  36. Sound of explosions taking place on other planets is not heard by a person on the earth. Give reason.
  37. A sonar device on a submarine sends out a signal and receives an echo 5 seconds later. Calculate the speed of the sound in water if the distance of the object from the submarine is 3625 m.
  38. Give two applications of ultrasound.
  39. Represent graphically two sound waves having same amplitude but different frequencies.
  40. . When the wire of a guitar is plucked, what types of waves are produced in (i) air and (ii) wire? Give reasons in support of your answer.
  41. A body is vibrating 6000 times in one minute. If the velocity of sound in air is 360 m/s, find : (a) frequency of vibration in hertz. (b) wavelength of the wave produced.
  42. Waves of frequency 200 Hz are produced in a string as shown in figure Find: (a) amplitude of the wave (b) wavelength of the wave (c) velocity of the wave
  43. Draw a graph showing a person with soft and loud voice.
  44. (a) Sound is produced when your school bell is struck with a hammer. Why? (b) Which characteristic of sound helps to identify your friend by his voice while sitting with others in a dark room?
  45. (a) Write factor on which pitch of a sound depends? (b) Draw a diagram to represent sound of (a) high pitch and (b) low pitch, of the same loudness.
  46. (a) Which wave property determines? (i) loudness (ii) pitch (b) Why are the ceilings of concert halls curved?
  47. . Give one difference between transverse and longitudinal wave. Give one example for each.
  48. What is an echo? Give minimum distance required to hear an echo. Give one application where principle of echo is utilised.
  49. (a) What type of wave is represented by density - distance graph? (b) What is meant by transverse wave? Give an example.
  50. What is transferred by a wave motion, matter or energy? Support your answer by an example.
  51. Derive a relation between wave velocity (v), wavelength (λ) and frequency (f).
  52. . Draw a diagram representing longitudinal wave.
  53. . What kind of wave is produced when sound energy propagates through air? Give two examples of longitudinal waves.
  54. What do you understand by the terms (i) compression (ii) rarefaction, as applied to longitudinal waves.
  55. A longitudinal wave is produced in a slinky, such that the frequency of the wave is 20 Hz and the speed of the wave is 30 cms–1. What is the minimum distance of separation between the consecutive compressions of the slinky?
  56. Wavelength of ripples produced on the surface of water is 0.14 m. If the velocity of ripples is 42 ms–1, calculate the number of ripples produced in one second.
  57. A boat at anchor is rocked by waves, such that distance between two consecutive crests is 100 m. If the wave velocity of the moving crests is 20 ms–1, calculate the frequency of rocking of the boat.
  58. A plastic ruler is held near the rotating wheel of a bicycle, such that it produces sound every time the spoke of the wheel strikes it. If 20 clicks are produced in 0.4s, calculate the frequency of sound produced.
  59. A bat can hear sound at frequencies up to 120 kHz. Determine the wavelength of sound in air at this frequency. Take the speed of sound in air as 344 ms–1.
  60. (a) Why the stage of an auditorium has curved background, curtains, carpets and false ceiling? (b) The sound of a ringing bell inside a vacuum chamber cannot be heard. Why?
  61. Ocean waves of time period 0.01s have a speed of 15 m/s. Calculate the wavelength of these waves. Find the distance between the adjacent crest and the trough.
  62. (a) How the bats make use of ultrasonic waves to catch their prey? Explain? 3 (b) A radar signal is reflected by an aeroplane and is received 2 × 10–5 s after it was sent. If the speed of these waves is 3 × 108 ms–1, how far is the aeroplane?
  63. . (a) Even if a loud explosion were to take place at any place on the moon, it would not be heard at a near by point. Give reason. (b) Explain in brief the dependence of speed of sound on nature of material medium and temperature. (c) Identify the two factors on which the loudness of sound depends.
  64. . (a) What causes reverberation of thunder sound ? (b) A Sonar device on a submarine sends a signal and receives an echo 5 s later. Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.
  65. Explain how defects in a metal block can be detected using ultrasound.
  66. Explain how human ear works in the transmission of sound wave to the brain.
  67. Define frequency, amplitude and speed of a sound wave.
  68. What is 'Ultrasound'? Explain how defects in a metal block can be detected using ultrasound.
  69. State the relationship between frequency and time period of a wave. The wavelength of vibrations produced on the surface of water is 2 cm. If the wave velocity is 16 m/s find its frequency and time period.
  70. Define echo. Establish a mathematical relation between speed of sound, distance of reflecting body from source of sound and time for echo.
  71. Distinguish between the following : (a) Mechanical Waves and Electromagnetic Waves ) Loudness and Intensity (c) Crest and Compression
  72. (a) Does the sound of a bomb explosion travel faster than the sound of the humming bee? (b) A sonar device on a submarine sends out a signal and receives an echo 5 s later. Calculate the speed of sound.
  73. (a) The sound of an explosion on the surface of lake is heard by a boatman 100 m away and a driver 100 m below the point of explosion. Of the two persons mentioned (boatman or driver) who would hear the sound first? And why? (b) Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
  74. (a) What is audible range of the average human ear? (b) Explain how ultrasound is used to clean spiral tubes and electronic components?
  75. . (a) Which wave property determines? (i) loudness (ii) pitch (b) Flash and thunder are produced simultaneously, but thunder is heard few seconds after the flash is seen, why?
  76. (a) Mention two practical applications of reflection of sound waves. (b) A sound wave travels at a speed of 339 m/s. If its wavelength is 1.5 cm, calculate the frequency of the wave.
  77. . What does acronym sonar stand for? What type of wave does it use? Write any two uses of sonar.
  78. . A sound wave has a frequency of 5000 Hz and wavelength of 20 cm. How long will it take to travel 1 km?
  79. . What is an echo? Why do we not get echo in small room?
  80. Waves of frequency 100 HZ are produced in a string as shown in Fig: Give it’s : (a) amplitude (b) wavelength (c) velocity


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