A siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m / s. Frequency of sound to be heard by the listener is (velocity of sound = 330 m / s )

Question

A siren emitting sound of frequency 800 Hz is going away from a static listener with a speed of 30 m / s. Frequency of sound to be heard by the listener is (velocity of sound = 330 m / s ) (A) 286.5 Hz (B) 481.2 Hz (C) 733.3 Hz (D) 644.8 Hz

Tardigrade Admin · Accepted Answer

The apparent change in the frequency of the source due to relative motion between source and observer is known as Doppler's effect. The perceived frequency

(n^{'})

when listener is static and source is moving away is given by

n^{'} = n (\frac{v}{v + v _{s}})

where

n

is frequency of source,

v

is velocity of sound and

v_{s}

is velocity of source.
Putting

v = 330 m / s, v_{s} = 30 m / s, n = 800 Hz

.

n^{'} = 800 \times (\frac{330}{330 + 30})

n^{'} = 733.3 Hz

In the limit when speed of source and observer are much lesser than that of sound

v_{1}

the change in frequency becomes independent of the fact whether the source is moved or the detector.

Q. A siren emitting sound of frequency $800 Hz$ is going away from a static listener with a speed of $30 m / s$ . Frequency of sound to be heard by the listener is (velocity of sound = $330 m / s)$

$286.5 Hz$

$481.2 Hz$

$733.3 Hz$

$644.8 Hz$

Q. A siren emitting sound of frequency 800Hz is going away from a static listener with a speed of 30m/s. Frequency of sound to be heard by the listener is (velocity of sound = 330m/s)

286.5Hz

481.2Hz

733.3Hz

644.8Hz

Q. A siren emitting sound of frequency $800 Hz$ is going away from a static listener with a speed of $30 m / s$ . Frequency of sound to be heard by the listener is (velocity of sound = $330 m / s)$

$286.5 Hz$

$481.2 Hz$

$733.3 Hz$

$644.8 Hz$