CBSE · Class 9 · Science · Chapter 10

Sound Waves: Characteristics and Applications

Explore how sound is produced, how it travels and how frequency, amplitude and wavelength determine its behaviour.

14 lessons 55 min
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Lessons in this chapter

  1. 1Production of SoundSound begins with vibration—from rubber bands and tuning forks to vocal cords and musical instruments.
  2. 2Propagation of SoundSound can travel through solids, liquids and gases, but it cannot propagate without a material medium.
  3. 3Sound WavesSound travels as moving compressions and rarefactions while medium particles merely oscillate about their mean positions.
  4. 4Energy of Sound WavesSound waves transfer energy through a medium, allowing them to make other objects vibrate.
  5. 5Graphical Representation of a Sound WaveA density graph turns invisible compressions and rarefactions into a readable wave pattern with crests and troughs.
  6. 6Wavelength, Frequency and Time PeriodWavelength describes spatial repetition, frequency counts oscillations per second, and time period measures the duration of one oscillation.
  7. 7Amplitude and Intensity of the Sound WavesAmplitude measures the size of density variation, while intensity measures the sound energy crossing unit area per unit time.
  8. 8Speed of SoundWave speed connects wavelength and frequency and changes strongly with the medium, temperature and humidity.
  9. 9Human Perception of SoundPitch, loudness and timbre describe how humans experience measurable wave properties.
  10. 10Reflection of SoundSound can bounce from surfaces and obey the same reflection geometry used for light.
  11. 11EchoAn echo is a reflected sound heard separately after a sufficient delay, making round-trip distance calculations possible.
  12. 12ReverberationClosely spaced multiple reflections make sound persist in large spaces and must be controlled for clarity.
  13. 13Ultrasonic and Infrasonic Waves, and their ApplicationsFrequencies outside human hearing reveal natural events, image the body, detect defects and locate objects through reflected sound.
  14. 14Chapter Summary and PracticeProduction, propagation, characteristics, perception, reflection and applications come together in one connected review.
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