Important points

  • Sound is a form of energy which produces the sensation of hearing.
  • Sound is produced due to vibrations in the body and travels in all directions away from the source.
  • Sound requires a medium for propagation. It cannot travel in vacuum.
  • Sound travel faster in solid than in liquids or gases. The velocity of sound is maximum in case of solids, lesser in the case of liquids and least in the case of gases.
  • The repetition of sound, when it is reflected from a distant body is called an echo.
  • Sonar is an instrument used for the measurement of the depth of sea. It is based on the principle of reflection of sound (echo).
  • Sounds having frequencies lower than 20 hertz are called infrasonic sounds.
  • Sounds having frequencies higher than 20,000 hertz are called ultrasonic sounds.
  • Sounds are generally classified into two broad categories (a) musical sound (b) noise.
  • Musical sound produces a pleasant effect in the ears. It is produced by periodic vibrations.
  • Noise produces an unpleasant effect to the ears. It is produced by non periodic vibrations.
  • The characteristics of sound which makes the sounds different from one another are (a) loudness (b) pitch and © quality or timbre.
  • The loudness of a sound produced by a body depends on (a) its amplitude (b) area of the vibrating body © distance between the source and the listener.
  • The pitch of the sound produced by a body depends on the frequency of vibration – greater the frequency of vibration greater is the pitch.