Question

An observer moves towards a stationary source of sound with a speed $1/5^{th}$ of the speed of sound. The wavelength and frequency of the source emitted are $\lambda$ and $f$ respectively. The apparent frequency and wavelength recorded by the observer are respectively :

• A. $1.2f,1.2\lambda$
• B. $1.2f,\lambda$
• C. $f,1.2\lambda$
• D. $0.8f,0.8\lambda$

Answer 1

Answer: (B)

$1.2f,\lambda$

Wavelength is constant, wavelength=$\lambda =constant$

Apparent frequency $f_{apparent}=\frac{\nu +{\nu }_0}{\nu }f$

$=(1+\frac{{\nu }_0}{\nu })f=(1+\frac{1}{5})f$

$=1.2f$