CBSE Class 9 Answered

(a) SONAR Stands for Sound Navigation and Ranging.

Sonar consists of a transmitter and a detector and is installed in a boat or a ship, as shown in figure.

The transmitter produces and transmits ultrasonic waves. These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector. The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted. The distance of the object that reflected the sound wave, can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound. Let the time interval between transmission and reception of ultrasound signal be tand the speed of sound through seawater be v. The total distance, 2d travelled by the ultrasound is then, 2d = v x t. The above method is called echo-ranging.

(b) Time between transmission and detection, t = 4s

Speed of ultrasound in sea water, v = 1550 m/s

Distance travelled by the ultrasound = 2 x depth of the sea

                                                          = 2d (where, d is depth of sea)