Question) An observer is approaching with a speed  v, towards a stationary source emitting sound waves of wavelength ${\lambda }_{0.}$ The wavelength shift defected by the observer is. (Take c = speed of sound )
$$\begin{gathered} \left(1\right) \frac{{\lambda }_{0}v}{c} \\ \left(2\right) \frac{{\lambda }_{0}c}{v} \\ \left(3\right) \frac{{\lambda }_0{v}^2}{c^2} \\ \left(4\right) Zero \end{gathered}$$