Question

Sound waves travel at $350\text{m/s}$ through a warm air and at $3500\text{m/s}$ through brass. The wavelength of a $700\text{Hz}$ acoustic wave as it enters brass from warm air

• A. Decrease by a factor 10
• B. Increase by a factor 20
• C. Increase by a factor 10
• D. Decrease by a factor 20

Answer 1

The correct option is C Increase by a factor 10

Here, $v_{\text{air}}=350\text{m/s}$, $v_{\text{brass}}=3500\text{m/s}$
When a sound wave travels from one medium to another medium its frequency remains the same
$\because$ Frequency, $f=\frac{v}{\lambda }$
Since $f$ remains the same in both the medium
$\Rightarrow \frac{v_{\text{air}}}{{\lambda }_{\text{air}}}=\frac{v_{\text{brass}}}{{\lambda }_{\text{brass}}}$
${\lambda }_{\text{brass}}={\lambda }_{\text{air}}\times \frac{v_{\text{brass}}}{v_{\text{air}}}={\lambda }_{\text{air}}\times \frac{3500}{350}=10{\lambda }_{\text{air}}$