Question

Ultrasonic waves are those sound waves having frequency; 1) between 20 hertz and 1000 hertz; 2) between 1000 hertz and 20000 hertz; 3) less than 20 hertz; 4) more than 20 kilohertz

Answer 1

Question :
Answer : Option (4) more than 20kilohertz
Even the audible frequency of human is 20hrtz to 2000hrtz. And a baby is 25hrtz to 2000hrtz.
...hope you got it

Answer 2

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                                    Ultrasonic vibrations

Ultrasonic vibrations have frequency more than 20,000 Hz or 20 k Hz

Thus OPTION 4 is correct :

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                                  Some more facts :

• Ultrasonic vibrations have a high wavelength

• Ultrasonic vibrations therefore deviate very less

• Thats why they are used in SONAR.

Hope it helps you ^_^

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