An obstacle is moving towards the source with velocity 'v'. The sound is reflected from the obstacle. If '…
An obstacle is moving towards the source with velocity 'v'. The sound is reflected from the obstacle. If ' $\mathrm{c}^{\prime}$ is the speed of sound and ${ }\lambda^{\prime}$ ' is the wavelength, then the
wavelength of the reflected wave $\left(\lambda_{r}\right)$ is
The frequency of reflected sound wave is $f_{r}=f\left(\frac{c+v}{c-v}\right)$
$\because$ No change in velocity occurs due to reflection of sound wave.
Hence,
$\begin{array}{l}
\frac{c}{\lambda_{r}}=\frac{c}{\lambda}\left(\frac{c+v}{c-v}\right) \Rightarrow \frac{1}{\lambda_{r}}=\frac{1}{\lambda}\left(\frac{c+v}{c-v}\right) \\
\lambda_{r}=\frac{c-v}{c+v} \lambda
\end{array}$