First slide

A source of sound S emitting waves of frequency 100 Hz and an observer O are located at some distance from each other. The source is moving with a speed of 19.4 ms-1 at an angle of 60° with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer 

(velocity of sound in air 330 ms-1, is




 Frequency of source, v0=100 Hz

 Velocity of source, vs=19.4 ms-1

 Velocity of sound in air, v=330 ms-1

As the velocity of source along the source observer line is vs cos 60° and the observer is at rest, so the apparent frequency observed by the observer is


=(100 Hz)330 ms-1330 ms-1-19.4 ms-112

=(100 Hz)330 ms-1330 ms-1-9.7 ms-1

=(100 Hz)330 ms-1320.3 ms-1=103 Hz

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