Wednesday, 13 June 2018

SOUND 9

     Practice Paper
    Subject Physics (2020)
        Class IX                              CH-15 SOUND                                         
                                        
I. Very Short Answer Type Questions: 

  1. If 20 waves are produced per second, what is the frequency in Hertz?
  2. The frequency of a source of sound is 10 Hz. How many times does it vibrate in a minute
  3. What type of wave is a sound? 
  4. What is an audible range of human ear?
  5. Define mechanical wave.
  6. Define wave motion.
  7. What is supersonic speed?
  8. Write a difference between longitudinal and transverse waves.
  9. What are the three quantities which play an important role in describing the nature of the wave.
  10. Define frequency.
  11. What is the time period?
  12. What is the unit of frequency?
  13. Write a relation between wavelength, frequency and wave speed.
  14. What are the factors that make the sound seem different to us?
  15. Define pitch.
  16. What is the relation between amplitude and loudness?
  17. What do you mean by the quality of musical sound?
  18. What is the frequency range of hearing of the human ear?
  19. Give one example of each of longitudinal and transverse wave.
  20. What is the frequency of wave with time period 0.025 s?
  21. Why do we hear the sound of an approaching car before the car reaches us?
  22. A baby recognizes her mother by her voice. Name the characteristic of sound involved.
  23. What is the unit of Wavelength of sound? 
  24. Infrasound is produced by:-(a) Bats (b) Dogs (c)Rhinoceros (d) Rats.
  25. Which of the following is used in echocardiography?
    (a) Ultrasound waves (b) Infrasound waves (c) X-Ray waves (d) Both a) and c).
  26. Speed of sound is maximum in :-(a) Solids  (b) Liquids  (c) Gases  (d) Plasma.
  27. Light is a (a) Longitudinal wave (b) Transverse wave (c) Both (d) None.
  28. In compression, pressure density is
    (a) High (b) Less (c) Remains the same (d) Maybe a) or b) depending upon disturbance.
  29. Frequency of an ultrasonic sound, the wave is
    (a) Greater than 20 Hz (b) Greater than 20,000 Hz (c) Greater than 2 Hz (d) Greater than 2Hz.
  30. Stethoscope  work on the principle of  :(a) Multiple reflections of sound (b)  Ultrasounds (c) Both a  and b.
  31. Audible The range of the human ear is :
    (a) 20 Hz  – 20 kHz. (b) 20 Hz  – 20  MHz (c) 20HZ  – 20,000 Hz  (d)  Both  a)  and  b).
  32. The  order of bones in the human ear from outside to inside:(a) Anvil,  Stirrup and Hammer. (b) Hammer, Anvil and stirrup (c) Stirrup, Hammer  and Anvil (d) Hammer, Stirrup and Anvil.

II. Short Answer Type Questions:
  1. Differentiate between longitudinal and transverse waves? 
  2. Define the terms 'crest' and 'trough' of a wave?
  3. Define wave motion.
  4. Draw figures to show the wave shapes of two sounds guitar and car horn. Which sound has a higher pitch? 
  5. Why do we say that sound waves are longitudinal waves?
  6. Define supersonic speed and sonic boom. 
  7. Define longitudinal and transverse waves.
  8. What do you mean by reverberation?
  9. Define the terms:- 1) Wavelength 2) Frequency.
  10. An underwater device detects ultrasounds of frequency 75 kHz towards the water surface. What is the wavelength of sound in the air above the water surface and what is its frequency? Speed of sound in air = 340m/s.
  11. What is an echo? Name two areas of its application?
  12. Establish the relation for a wave that velocity = frequency X wavelength.
  13. When a wave travels from one medium to another, the wavelength changes but not the frequency. The wavelength of sound disturbance 30 cm in air and of the wave velocity is 340 m/s. What will be the wavelength of this disturbance in Helium & water? The speed of sound in helium is 970 m/s and 1450 m/s in water.
  14. Sound waves of wavelength λ travel from a medium in which its velocity is v m/s into another medium in which if velocity is 3 v m/s. What is the wavelength of the sound λ in the second medium? 
  15. Why are sound waves called as mechanical waves? 
  16. Define: (a) Time Period (b) Amplitude of a wave. 
  17. Write the differences between noise and music.
  18. What do you understand by loud and soft sound?
  19. A sound wave travels at a speed of 340m/s. If the wavelength of a wave is 1.4m travel. What is the frequency of the wave?
  20. Sound requires a medium to travel Justify experimentally.
  21. Explain how echoes are used by bats to locate obstacles and pray in front of them. 

III. Long Answer Type Questions:

  1. Sound cannot travel in a vacuum. Describe an experiment to demonstrate this.
  2. What are crest and trough of a wave?
  3. Explain the working and application of sonar.
  4. Explain the structure of the human ear with the help of a diagram.
  5. A cork on the surface of water moves up-down completing five vibrations in 4s.The waves travel from cork to the shore which is 20m away, in 10s calculate (a) the speed (b) frequency (c) wavelength.
  6. An observer far away from a railway station hears the train starts. The sound arrives both from the steel rails and through the air with a time difference of 3.5s.How far is the railway station from the observer? 
  7. The speed of sound in air and steal is 340m/s and 5130m/s respectively? How can ultrasound be used to detect the defect in the metal block?
  8. What do you understand by low pitched and high pitched sound?
  9. Why do we see light first and hear the sound later during a thunderstorm?
  10. What are the laws of reflection of sound?
  11. Why are the ceilings of concert halls curved?
  12. What is reverberation? What is done to reduce it?
  13. A man standing in a valley between two parallel mountains fires a gun and hears echo at an interval of 2 s and 3.5s. What is (a) the distance between two mountains (b) the location of the man with respect to the mountain?
  14. What is SONAR? Write its working?
  15. A stone is thrown in a pond. 12 full ripples are produced in a second. If the distance between a crest and a trough is 10 cm, calculate the wavelength and velocity of the wave.
  16. Why is lightning seen before the sound of thunder heard? What causes the reverberation of thunder sound?
  17. Write a factor on which pitch of a sound depends?
  18. Draw a diagram to represent the sound of (a) high pitch. (b) the low pitch of a sound.

NCERT QUESTIONS:

  1. How does the sound produced by a vibrating object in a medium reach your ear?
  2. Explain how sound is produced by your school bell.
  3. Why sound waves are called mechanical waves?
  4. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
  5. Which wave property determines (a) loudness, (b) pitch?
  6. Guess which sound has a higher pitch: guitar or car horn?
  7. What are wavelength, frequency, time period and amplitude of a sound wave?
  8. How are the wavelength and frequency of a sound wave related to its speed? 
  9. Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
  10. A person is listening to a tone of 500 Hz sitting at a distance of 450m from the source of the sound. What is the time interval between successive compressions from the source?
  11. Distinguish between loudness and intensity of sound.
  12. In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?
  13. An echo returned in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342m/s?
  14. Why are the ceilings of concert halls curved?
  15. What is the audible range of the average human ear?
  16. What is the range of frequencies associated with (a) Infrasound? (b) Ultrasound?
  17. A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in saltwater is 1531 m/s, how far away is the cliff?
  18. What is sound and how is it produced?
  19. Describe with the help of a diagram, how compressions and rarefactions are produced in the air near a source of the sound.
  20. Cite an experiment to show that sound needs a material medium for its propagation.
  21. Why the sound wave is called a longitudinal wave?
  22. Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
  23. Flash and thunder is produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
  24. A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 m s–1.
  25. Two children are at opposite ends of an Aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in the air and in Aluminium to reach the second child.
  26. The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute
  27. Does sound follow the same laws of reflection as light does? Explain.
  28. When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?
  29. Give two practical applications of reflection of sound waves. 
  30. A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g = 10 m s–2 and speed of sound = 340 m s–1.
  31. A sound wave travels at a speed of 339 m s–1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
  32. What is reverberation? How can it be reduced?
  33. What is the loudness of sound? What factors does it depend on?
  34. Explain how bats use ultrasound to catch prey.
  35. How is ultrasound used for cleaning?
  36. Explain the working and application of a sonar.
  37. A sonar device on a submarine sends out 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.
  38. Explain how defects in a metal block can be detected using ultrasound.
  39. Explain how the human ear works.

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