Question

In SONAR, what is used?
A. Ultrasonic waves
B. Infrasonic waves
C. Radio waves
D. Audible sound waves

Answer 1

Hint: SONAR is used by submarines underwater, where a higher frequency sound wave is used.

Complete step by step answer:
Sound Navigation and Ranging (SONAR) is a technology used to detect obstacles in a path. In this method, ultrasonic waves are emitted by a body. When the ultrasound waves hit an object in its path, they get reflected. The reflected sound waves are picked up by the emitting body through a receiver. By calculating the time interval between the emission and reception of the sound waves and the speed of the ultrasound in the medium that they have been released into, the distance between the emitting body and the object can be found out.
$\text{Distance between object and body = }\dfrac{\text{Speed of ultrasound in the medium}\times \text{Time interval }}{2}$
In the formula above, the factor 2 comes in the denominator because the ultrasound travels the whole distance twice, once from the body to the obstacle and one more time from the obstacle to the body after reflection.
This technology is especially used in submarines underwater to find out obstacles in their path, enemy submarines and height above the sea bed.
Ultrasound and not any other sound wave are used in SONAR for two reasons. Firstly, ultrasound has a higher frequency and hence higher energy than audible sound waves, so they can move easily underwater and are not stopped by small obstacles.
Secondly, they are above the human audible range, so they won’t get mixed with other noises made by humans, engines and other machines.
So, ultrasound or ultrasonic waves are used in SONAR.
So, the correct answer is A) Ultrasonic waves.

Note: Students may make a mistake and mark audible sound waves by thinking of the full form of SONAR which only mentions sound. Their basic instinct would tempt them to mark the wrong option.
However, keeping in mind the use of SONAR in submarines and the reasons why ultrasonic waves are used, students should be able to relate and answer correctly.