Question

A source moving with velocity $V_s$ approaches a stationary observer. Then, the apparent changes in the wavelength of the sound waves is

• A. wavelength increases by an amount $\frac{V_s}{V}\lambda$
• B. wavelength decreases by an amount $\frac{V_s}{V}\lambda$
• C. wavelength does not change
• D. wavelength may increase or decrease

Answer 1

Answer: (B)

wavelength decreases by an amount $\frac{V_s}{V}\lambda$

apparent frequency $f_1=\frac{v}{v-v_s}f$

then ${\lambda }_1=\frac{v-v_s}{v}\lambda$

therefore change in wavelength is $\lambda -{\lambda }_1=\frac{v_s}{v}\lambda$