Question

The wavelength of the upper limit of the audible sound in air, is .

• A. $17\text{cm}$
• B. $17\text{mm}$
• C. $17\text{nm}$
• D. $17\mu \text{m}$

Answer 1

The correct option is B $17\text{mm}$

Audible sound is the sound that can be heard by an adult human being, i.e. in the range of frequency $20\text{Hz}-20,000\text{Hz}$, whose upper limit is $20,000\text{Hz}$.
$⟹$ Frequency, $\text{f}=20000\text{Hz}$
Speed of sound in air, $\text{v}=340\text{m}{\text{s}}^{-1}$
If $\lambda$ is the sound's wavelength, then $\text{v}=\lambda \times \text{f}$
$⟹\lambda =\frac{\text{v}}{\text{f}}=\frac{340}{20000}$
$=\frac{34}{2}\times {10}^{-3}\text{m}$

$\lambda =17\times {10}^{-3}\text{m}=17\text{mm}$