SONAR emits which of the following waves ?

The correct option is ultrasound.

Step-by-step Explanation:

1. Understanding SONAR:
SONAR stands for SOund Navigation And Ranging. It is a technology and system that uses sound propagation to navigate, communicate with, or detect objects on or under the surface of the water, such as vessels, submarines, or the seabed.

2. Type of Waves Used:
SONAR systems operate by emitting acoustic (sound) waves into the water and listening for echoes reflected back from underwater objects. Specifically, they utilize ultrasonic waves (or ultrasound).

3. Why Ultrasound?
Ultrasonic waves are sound waves with frequencies higher than the upper limit of human hearing, which is typically above 20 kHz (kilohertz). These high-frequency waves are preferred because:
- They have a shorter wavelength, allowing them to detect smaller objects and provide better resolution.
- They can travel long distances through water with minimal attenuation (loss of energy) compared to electromagnetic waves like light or radio waves, which are rapidly absorbed by water.

4. Comparing Options:
- Radio waves: These are electromagnetic waves and are rapidly absorbed by water, making them unsuitable for underwater navigation or detection.
- Light waves: Light is also an electromagnetic wave and cannot penetrate deep or turbid water, limiting its range significantly.
- Ultrasound: These are mechanical sound waves that propagate efficiently through water, making ultrasound the correct choice.