A police siren contains two frequencies, producing a wavering sound (beats). Explain how the siren sound changes as a police car approaches, passes, and moves away from a pedestrian.


Answered 1 year ago
Answered 1 year ago
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Observed frequency fof_o in one-dimensional problem due to Doppler effect is given with:

fo=fvsoundvsound±vsource(1)f_o = f \cdot \frac{v_{sound}}{v_{sound} \pm v_{source}} \tag{1}

In Eq. (1), we use the plus sign if the source moves away from the observer and minus if it moves toward the observer.

Also, beat frequency fbf_b is defined as:

fb=f1f2(2)f_b = \abs{f_1 - f_2} \tag{2}

In Eq. (2), f1f_1 and f2f_2 are frequencies of individual sources.

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