Determination of the depth of a well: Depth of water surface of a well can be very easily determined by means of echo. When a sound is produced at the mouth of the well, it being reflected from its water surface heard in the form of echo. The time between the production of sound and the hearing of echo is determined by means of a stopwatch.


Let, depth of well = h

the time difference between the production of sound and hearing of echo = t

Speed of sound = v

Now the distance travelled by reflected sound to the listener is 2h.

Therefore, 2h = V x t

or, h = (V x t)/2, If the depth of the well is less than 16.6m, it will not be possible to perform this experiment as it is based on echo.

In the same way this method can also be used to find mineral substances in the earth.


Flying of bat:


Bat flies using the echo of sound as it cannot see. Bat can produce and hear ultrasonic sound. We cannot hear ultrasonic sound Bat produces ultrasonic sound and spread it forward which reflects back to the bat from a reflector. Bat can understand from the reflected sound if there is any object before it. It hunts its prey using this technique. If the sound does not reflect back then it can understand that there is open space and it flies that way. Sometimes the bat fails to detect the position of wires of electric lines and flies through the parallel wires and gets stuck and becomes dead as soon as the positive and negative electric lines get connected with its body. This is why sometimes bats are found hanging dead from electric lines.

Bat can produce and hear the sound of frequency about 1.00.000 Hz.