Ultrasonic waves are those sound waves having frequency __________?
Correct answer: D. more than 20 kilohertz
- A. between 20 hertz and 1000 hertz
- B. between 1000 hertz and 20000 hertz
- C. less than 20 hertz
- D. more than 20 kilohertz
Explanation
Ultrasonic sound has a frequency above the upper limit of normal human hearing, conventionally more than 20 kilohertz. Frequencies below 20 hertz are called infrasonic.
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Inventions and Discoveries covers the people, dates, principles and practical uses behind developments such as the wheel, printing press, telephone, electricity, radio, computer, internet, vaccines and space technology. It distinguishes an invention, which creates a device or process, from a discovery, which identifies something already present in nature.
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