Ultrasound is

• A. Sound which has a frequency above the range of the human ear
• B. Sound which has a frequency within the range of the human ear
• C. Sound produced by mechanical devices
• D. Sound that travels only in air

Answer: (A)

Ultrasound is sound with a frequency above the range of human hearing. Humans typically hear up to about 20 kHz, so anything above that threshold is considered ultrasound. This frequency boundary is what sets ultrasound apart and is why it’s used in nondestructive testing for high-resolution imaging and flaw detection. The other statements don’t define ultrasound: audible sound falls within human hearing; being produced by mechanical devices is too generic and doesn’t specify the frequency; and ultrasound can travel through solids, liquids, and gases, not just air.