Question

A source producing sound of frequency 170 Hz is approaching a stationary observer with a velocity 17 m$s^{-1}$. The apparent change in the wavelength of sound heard by the observer is (speed of sound in air = 340 m$s^{-1}$)

• A. 0.1 m
• B. 0.2 m
• C. 0.4 m
• D. 0.5 m

Answer 1

The correct option is A

0.1 m

$\lambda =\frac{v}{n}=\frac{340}{170}=2m,nl=\frac{340}{340-17}\times 170\Rightarrow n^{\prime }=178.9Hz$

Now ${\lambda }^{\prime }=\frac{v}{n^{\prime }}=\frac{340}{178.9}$ = 1.9

$\Rightarrow \lambda -{\lambda }^{\prime }=2-1.9=0.1$