Question

Frequency of Ultrasonic waves is .................
A. Less than 20000 Hz
B. Greater than 20000 Hz
C. Less than 20 Hz
D. 1000 Hz

Answer 1

Humans can hear sounds with frequencies ranging from 20 Hz to 20,000 Hz. Sound waves have wavelengths ranging from 17 m (56 ft) to 17 mm in air at normal temperature and pressure (0.67 in). A velocity vector is formed by combining speed and direction; a wave vector is formed by combining wave number and direction.

Complete step by step solution:
Ultrasound refers to sound waves having frequencies greater than the human hearing limit. Ultrasound has the same physical qualities as "regular" (audible) sound, except that humans cannot hear it. In healthy young people, this limit varies from person to person and is around 20 kilohertz (20,000 hertz). Ultrasound machines use frequencies ranging from 20 kHz to several gigahertz. The American National Standards Institute defines ultrasound as "sound at frequencies higher than 20 kHz." Ultrasonic waves have wavelengths of 1.9 cm or less in air at atmospheric pressure. The top frequency limit in humans (about 20 kHz) is related to middle ear restrictions. When high-intensity ultrasound is delivered directly into the human skull and reaches the cochlea by bone conduction rather than going through the middle ear, auditory sensation can ensue. Because the maximum pitch of hearing in humans tends to diminish with age, children can hear some high-pitched noises that older adults cannot.
Hence option B is correct.

Note:
Ultrasound is used in a variety of applications. Objects are detected and distances are measured using ultrasonic instruments. In medicine, ultrasound imaging, also known as sonography, is often used. Ultrasound is used to identify faults in goods and buildings during nondestructive testing. Ultrasound is utilised in industry for cleaning, mixing, and speeding up chemical processes. Ultrasound is used by bats and porpoises to locate prey and barriers.