An observer is moving with speed $v_0$ towards a stationary source emitting a sound wave of wavelength $\lambda$ The change in wavelength detected by the observer is (v = speed of sound)

• A

  $\frac{v}{v_0}\lambda$

• B

  $\frac{v_0}{v}\lambda$

• C

  $\frac{v_0^2}{v}\lambda$

• D

  zero