1. Human Audible Range: The human ear is typically capable of hearing sounds with frequencies ranging from approximately 20 Hz to 20,000 Hz (or 20 kHz). This range is known as the sonic or audible frequency range.
2. Defining Ultrasonic Waves: Ultrasonic waves are sound waves that have a frequency higher than the upper limit of human hearing. Therefore, any sound wave with a frequency
greater than 20 kHz is classified as ultrasonic.
3. Characteristics and Applications:
• These waves have very short wavelengths, allowing them to be focused into narrow beams.
• They are used in various fields, such as medical imaging (ultrasound), non-destructive testing of materials, and underwater depth measurement (SONAR).
• Note: Waves with frequencies below 20 Hz are called "Infrasonic" waves.
In summary, because ultrasonic waves exist beyond our hearing capacity at the high end of the spectrum, the correct definition is frequencies more than 20 kHz.