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.
CALCULATION OF MINIMUM DISTANCE TO HEAR AN ECHO
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).
HEARING AID
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
