Ultrasonic and Infrasonic Waves: The sound having frequency 20 Hz to 20 kHz is called audible sound. Human ear cannot hear sound of frequencies lying outside this range. The limits of audibility of sound vary from individual. Generally, the upper limit decreases with an increase of age of individual, usually, and people cannot hear sound of frequency more than 15 kHz. Sound of frequencies below 20 Hz are called infrasonics, while frequencies beyond 20 kHz are called ultrasonics. Ultrasonics can be heard by dogs, cats, bats, etc. Bats detect the path by means of ultrasonics. Ultrasonics can be used for diagnosis of tumors and other abnormalities within our body. This is known as ultrasonography. Ultrasonics are used to cure various diseases and to measure the depth of oceans to detect submarines.

• Then the speed of infrasonics, audible, and ultrasonics waves are vᵢ > vₐ > vᵤ.
• vᵢ = vₐ = vᵤ.
• vᵢ < vₐ.
• vᵢ > vₐ, vᵤ.

Sound waves can be categorized based on their frequencies, which are measured in hertz (Hz). The range of sound that humans can hear is known as audible sound, typically between 20 Hz and 20 kHz. However, this range can vary from person to person, and as people age, their ability to hear higher frequencies often diminishes, with many unable to hear sounds above 15 kHz.

Types of Sound Waves

• Infrasonic Waves: These are sound waves with frequencies below 20 Hz. Humans cannot hear them, but they can be detected by some animals.
• Audible Waves: This is the range of sound that humans can hear, from 20 Hz to 20 kHz.
• Ultrasonic Waves: Frequencies above 20 kHz fall into this category. While humans cannot hear these sounds, many animals, such as dogs and bats, can.

Applications of Ultrasonics

Ultrasonic waves have various practical uses, including:

• Medical Diagnosis: Ultrasonography uses ultrasonic waves to create images of internal body structures, helping in the detection of tumors and other abnormalities.
• Treatment: Ultrasonics are employed in certain medical therapies to treat various conditions.
• Navigation and Detection: Bats use ultrasonic waves to navigate and locate prey, while humans use them to measure ocean depths and detect submarines.

Speed of Sound Waves

The speed of sound varies among these types of waves, with infrasonic waves traveling faster than audible sound, which in turn travels faster than ultrasonic waves. This can be summarized as:

• Speed Order: vᵢ (infrasonic) > vₐ (audible) > vᵤ (ultrasonic)

Understanding these differences helps us appreciate the diverse ways sound interacts with our environment and its applications in technology and nature.