06 Echo

  • Echo is the repetition of sound caused by the reflection of sound waves reflection from the surface of a large obstacle.
  • An echo is simply a reflected sound.
  • Echo creates a persistence of sound even after the source of sound has stopped vibrating.
  • Applications of Echo:
    • Echo is used by bats and dolphins to detect obstacles or navigate.
    • SONAR and hearing aids also use this principle.


  • We can hear the original sound and the reflected sound (echo) separately only if there is a time-interval (or time gap) of at least

    th of a second.

  • The minimum distance of the obstacle from the source of sound to a sound reflecting surface (wall, etc.) to hear an echo is 17.2 metres (at 20oC).


The sound waves are received by the hearing aid and are reflected into a narrower area leading to the ear.

SONAR (Sound Navigation And Ranging)

  • Sonar is a device used in oceanographic studies, that uses ultrasonic waves to measure the distance, direction and speed of underwater objects like shoals of fish, shipwrecks, and enemy submarines.
  • The sonar device measures the time taken by the ultrasonic sound pulse to travel from the ship to the bottom of the sea, and back to the ship.
  • Half of this time gives the time taken by the ultrasonic sound to travel from the ship to the bottom of the sea.
  • A sonar apparatus consists of two parts:
    • (i) A transmitter (for emitting ultrasonic waves), and
    • (ii) A receiver (for detecting ultrasonic waves).

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