Echo is formed when a sound is reflected by large, hard and flat surfaces like buildings, walls and cliffs. It is a distinct, reflected sound wave from a surface. Sometimes, we will hear many echoes when there are many reflecting surfaces.
Note that reflection of sound occurs just like the reflection of light.
Application of Echo
(1) If the total time taken includes time taken for returning echo,
(2) However, if the total time taken does not include time taken for returning echo, then use normal formula to calculate speed.
A fishing boat uses a sonar to detect a shoal of fish. A short pulse of sound waves is emitted from the boat, and the echo from the shoal is detected 0.1 s later. The waves travel through sea water at 1500 m/s. How far below the boat is the shoal of fish?
Speed of sound = distance⁄(time taken/2)