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Sound from a point isotropic source spre...

Sound from a point isotropic source spreads equally in all directions in homogeneous medium. Therefore its intensity decreases with square of distance from the source. When distance between observer and the source changes, apart from changes in intensity, the observer listens sound of pitch higher or lower than actual pitch depending upon the fact that the distance between the observer and source is decreasing or increasing respectively. An observer O is at a distance 2R from centre of a circle of radius R. A point isotropic sound source S moves on the circle with uniform angular velocity`omega = pi//3 " rad"//s`. Initially observer, source and centre of the circle are in same line.


During a complete round trip of star on the circle, the observer listens a sound, whose –

A

wavelength first decreases to a maximum value then increases to the original value

B

wavelength first increases to a maximum value then decreases to the original value

C

During the first half time wavelength increases then decreases to the original value

D

None of the above is correct because in Doppler's effect, it is the pitch of sound which changes and not its wavelength, irrespective of motion of source or observer.

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