Question

Sound waves travel at 350 m s–1 through a warm air and at 3500 m s–1 through brass. The wavelength of a 700 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

Answer: (C)

Increase by a factor 10

Answer 2

Here, $v_{air} = 350ms^{- 1},v_{brass} = 3500ms^{- 1}$

When a sound wave goes from one medium to another medium, its frequency ($\upsilon$) remains the same.

Frequency, $\upsilon = \frac{Velocity}{Wavelength} = \frac{v}{\lambda}$

Since $\upsilon$remains the same in both the media, so

$\frac{V_{air}}{\lambda_{air}} = \frac{V_{brass}}{\lambda_{brass}}$

Or $\lambda_{brass} = \lambda_{air} \times \frac{v_{brass}}{v_{air}} = \lambda_{air} \times \frac{3500}{350} = 10\lambda_{air}$