Physics - Sound Wave Question with Solution | TestHub

When a source of sound moves towards a stationary observer, the apparent frequency $n^{\prime }$ heard by the observer is given by Doppler's effect:

$n^{\prime }=n\left(\frac{v}{v-v_s}\right)$

Since $v-v_s<v$, the apparent frequency increases ($n^{\prime }>n$).

The apparent wavelength ${\lambda }^{\prime }$ is given by:

${\lambda }^{\prime }=\frac{v-v_s}{n}$

Since $v-v_s<v$, the apparent wavelength decreases (${\lambda }^{\prime }<\lambda$).

Thus, the apparent frequency increases while the wavelength decreases.

Answer: increases while wavelength decreases.