SONAR

The word ‘SONAR’ stands for ‘Sound Navigation and Ranging’/

PRINCIPLE OF SONAR:

Sonar is an apparatus which is used to find the depth of a sea or to locate the under water things like shoals of fish, enemy submarines etc. Sonar works by sending short bursts of ultrasonic sound from a ship down into sea-water and then picking up the echo produced by the reflection of ultrasonic sound from under-water objects like bottom of sea, shoal of fish, a submarine.

WORKING OF SONAR:

A sonar apparatus consists of two parts :

(i) A transmitter (for emitting ultrasonic waves) and (ii) a receiver (for detecting ultrasonic waves). Now suppose a sonar device is attached to the under-side of a ship and we wan to measure the depth of sea (blow the ship). To do this, the transmitter of sonar is made to emit a pulse of ultrasonic sound with a very high frequency of about 50,000 hertz. This pulse of ultrasonic sound travels down in the sea-water towards the bottom of the sea . When the ultrasonic sound pulse strikes the bottom of the sea, it is reflected back to the ship in the from of an echo. This echo produces an electrical signal in the receiver part of the sonar device. 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.

Depth of sea =

Ex. The ultrasonic waves take 6 seconds to travel from the ship to the bottom of the sea and back to the ship.What is the depth of the sea ? (Speed of sound in water = 1500 m/s.)

Solution: The time taken by the ultrasonic sound waves to travels from the ship to the sea-bed and back to the ship is 6 seconds. So, the time taken by the ultrasonic sound to travel from the ship to sea-bed with be half of this time, which is seconds. This means that the sound takes 2 seconds to travel from the ship to the bottom of the sea.

Now, Speed =

So, 1500 =

And, Distance = 1500 × 3 m = 4500 m