1.8 Short Notes: Sound Waves

Sound waves

  • Sound waves are produced by vibrations.
  • The vibrations cause compression and rarefaction of air molecules.
  • Sound waves need a medium to travel (We cannot hear any sounds in vacuum space).


Figure 1.33 shows the graph of loudness. To decrease the loudness, the amplitude should be reduced while increasing the amplitude will raise the loudness.


Figure 1.34 shows the graph of the pitch of the sound waves. To reduce the pitch, the wavelength of the sound wave should be increased while reducing the wavelength will increase the pitch.

Reflection of sound waves

Example question on reflection on sound wave

An audio engineer want to test a new speaker in the ballroom. The ballroom is 45m long. Find the time taken for the sound to return to the speaker. (Velocity of sound = 343 m/s)



  1. Why do astronauts cannot hear any sounds in outer space?
  2. How music was formed?
  3. 3.An electronic music is being played in a club. It took 0.15s for the music to reflect. The velocity of the music is 358 m/s. What is the length of the club?


  1. The outer space is a vacuum.
  2. Music can be created by changing the loudness and the pitch of the sound waves. Therefore, music notes are formed.
  3. 26.9m.