Chapter 11

NCERT
Class 9
Science
Solutions
6. A person has a hearing range from 20 Hz to 20 KHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 ms–1?

Question:

A person has a hearing range from 20 Hz to 20 KHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 ms–1?

Answer:

Speed of sound in air v = 344 ms–1

Frequency v = 20 Hz

Wavelength λ = ?

From, Velocity = wavelength × frequency

344 ms–1 = λ× 20 Hz

λ = 344 ms–1 / 20 Hz

λ = 17.2 m

λ = 17.2 m / 1000

[For v = 20 KHz or 20000 Hz]

λ = 0.0172 m

This is, the wavelengths of sound corresponding to the range from 20 Hz to 20 KHz are 17.2m and 0.0172m respectively.

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