Question

In SONAR, we use :

• A. Audible Sound
• B. Radio Sound
• C. Ultra Sound
• D. Infra Sound

Hint:

Remember the sound spectrum: - {Infrasound} (\(<20 \ \text{Hz}\)): Long wavelength, travels far, used by large animals (elephants, whales) for communication, associated with earthquakes. - {Audible Sound} (\(20 \ \text{Hz} - 20 \ \text{kHz}\)): What humans hear. - {Ultrasound} (\(>20 \ \text{kHz}\)): Short wavelength, high directionality. Used in SONAR, medical imaging (sonograms), non-destructive testing, and by animals like bats and dolphins for echolocation. The choice of ultrasound for SONAR is driven by its ability to provide detailed information about underwater environments and objects.

Answer 1

The Correct Option is C

Concept: SONAR is a technology used primarily for underwater detection and navigation. It relies on sound waves. Step 1: Understanding SONAR SONAR is an acronym for SOund NAvigation and Ranging. It works by emitting sound pulses and then detecting the echoes that return after these pulses reflect off objects. By measuring the time delay between the emission of the pulse and the reception of the echo, the distance to the object can be determined. Step 2: Classifying Sound Waves by Frequency Sound waves are categorized based on their frequency:
Infra Sound (Infrasonic waves): Frequencies below the range of human hearing, typically less than \(20 \ \text{Hz}\).
Audible Sound: Frequencies within the range of human hearing, typically from \(20 \ \text{Hz}\) to \(20,000 \ \text{Hz}\) (or \(20 \ \text{kHz}\)).
Ultra Sound (Ultrasonic waves): Frequencies above the range of human hearing, typically greater than \(20,000 \ \text{Hz}\) (or \(20 \ \text{kHz}\)). Note: "Radio Sound" is not a standard classification for sound waves used in this context. Radio waves are electromagnetic waves, not sound waves, and are used in RADAR, not typically SONAR. Step 3: Why Ultra Sound is Used in SONAR Ultrasonic waves are chosen for SONAR applications due to several advantageous properties:
High Frequency and Short Wavelength: Ultrasonic waves have high frequencies, which mean they have short wavelengths (since wavelength \(\lambda = v/f\), where \(v\) is the speed of sound and \(f\) is frequency). Short wavelengths are less prone to diffraction (bending around obstacles) and can be focused into narrow beams. This allows for better resolution in detecting smaller objects and determining their direction more accurately.
Good Directionality: Because they can be directed in a narrow beam, they are not easily scattered in all directions. This is crucial for pinpointing the location of an object.
High Energy: Ultrasonic waves can be produced with high energy, allowing them to travel longer distances in water without significant loss of intensity. Audible sound waves have longer wavelengths and would spread out more, making it harder to detect small objects or determine their precise location. Infrasound has very long wavelengths and is generally not suitable for the detailed ranging and imaging tasks SONAR is used for. Therefore, Ultra Sound is the type of sound used in SONAR systems.