A whistle emitting a sound of frequency 440 Hz is tied to a string of 1.5 m length and rotated with an angular velocity of 20 rad s -1 in the horizontal plane. Calculate the range of frequencies heard by an observer stationed at a large distance from the whistle in same horizontal plane. (v sound = 330 m/s)
Text Solution
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(f max = 484 Hz, f min = 403.3 Hz)
V s = Speed of source (whistle)
= Rω
= (1.5) (20) m/s
V s = 30 m/s
Maximum frequency will be heard by the observer O in position P of whistle and minimum in position Q of whistle. Now–
f max = f 
where V = Speed of sound in air
= 330 m/s
= (440) 
Hz
f max = 484 Hz
and f min = f 
= (440) 
f min = 403.33 Hz
Therefore, range of frequencies heard by observer is form 403.33 Hz to 484 Hz.
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