Question

A ship sends on a high frequency sound wave and receives an echo after 1 second. What is the depth of the sea? Speed of sound in water is 1500 m/s.
A. 375m
B. 750m
C. 1500m
D. 2250m

Answer 1

Hint: SONAR, (SOund Navigation And Ranging), is a technological device based on the principle of reflection of sound. An ultrasonic wave is transmitted from Sonar towards the bottom of sea or ocean resulting in waves coming back after reflection from the object or a submarine. We will calculate the total distance travelled by the sonar waves and distance, speed, time relation will give the velocity of the sonar wave.

Complete step-by-step answer:
Given,
velocity =1500m/s
time= 1s
We will write the expression to find out the depth of the sea that is X. The sound wave has to travel a distance of 2X to come back to the ship.
$ \Rightarrow 2X = vt$
Here v = 1500 m/s is the velocity of the wave and t is the time taken.
$
 \Rightarrow 2X = 1500\,m/s \times 1\,s\\
 \Rightarrow X = 750\,m
$

Therefore, the correct option is B.

Additional Information: Sonar is a device used for finding objects underwater using sound waves. Sonars transmit ultrasonic waves into the water below the ship and receive the returning echoes from the sea-bed. Any object that gets hit by these ultrasonic waves will emit a returning echo that will show up on the sonar display. The device which emits the ultrasonic waves is known as a transducer. Sonar, sound navigation and ranging, is a technique for the purpose of detecting and determining the distance and the direction of underwater objects by acoustic means. Sound waves emitted by or reflected from the object underwater are detected by sonar apparatus and analysed for the information they contain.

Note: The basic principle of Sonar is reflection and receiving the echoes from the target. While calculating the distance travelled by the sound wave, we have to double the distance between the object and the submarine since echo’s transmission and reception involves the reflection of sound wave from the target.