CBSE Class 9 Answered

When a sound signal( ultrasonic)  is sent into the water, part of it will be reflected back if it strikes an object or "target". The distance to the object can be calculated by measuring the time between when the signal is sent out and when the reflected sound, or echo, is received. For example, if four seconds elapse between the emission of the outgoing sound and the return of its echo, the sound has taken two seconds to travel to the object and two seconds to return. The average speed of sound in the water is 1,500 meters per second. So if it takes two seconds for sound to reach the object, we can assume the object is 2 sec x 1,500 m/sec or 3,000 meters away.

Sonar systems generally use highly directional beams of sound when searching for targets. In this way they are able to determine direction to the target, as well as the distance.

Relection and absorbtion of sound depends on the frequency used

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