Question

Apparent frequency of sound is 505 Hz when the listener is approaching a stationary source of sound with a velocity 1% of the velocity of sound in air. The actual frequency of sound is

• A. 470 Hz
• B. 480 Hz
• C. 490 Hz
• D. 500 Hz

Answer 1

The correct option is D 500 Hz

Given : $\delta =505H_z$

$\frac{v_0}{v}=\frac{1}{100}\Rightarrow v_0=\frac{v}{100}$

By doppler effect formula:

${\delta }^{{}^{\prime }}=\delta \left(\frac{v-v_0}{v-v_3}\right)$

$505=\delta \left(\frac{v-\frac{v}{100}}{v}\right)$

$505\frac{100}{101}=\delta$

$\Rightarrow \delta =500H_z$