Question

The wavelength is 120 cm when the source is stationary. If the source is moving with relative velocity of 60 m/sec towards the observer, then the wavelength of the sound wave reaching to the observer will be (velocity of sound = 330 m/s)

• A. 98 cm
• B. 140 cm
• C. 120 cm
• D. 144 cm

Answer 1

The correct option is A

98 cm

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

$\Rightarrow {\lambda }^{\prime }=120\left(\frac{330-60}{330}\right)=98cm.$