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

Answer: (A)

98 cm

Answer 2

$n^{'} = n\left( \frac{v}{v - v_{s}} \right)$ ⇒ $\lambda^{'} = \lambda\left( \frac{v - v_{S}}{v} \right)$

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