Doppler Effect

physics lessons Doppler Effect

When we are on a car circuit, we see that when a race car F1 approaches, its sound’s pitch is higher and when it travels away, its sound’s pitch is lower.
What is this ?
This is due to the shift in frequency and wavelength of waves or called Doppler Effect.
The frequency heard by an observer is higher when the source approaches the observer and lower when the source moves away from the observer.

How do we explain this Doppler effect ?
when the race car is at rest : Theconcentric circles illustrate the peak of wave. The distance between twoo circles equals the wavelength of sound. Here the wave received per second by the observer equals the number of waves emitted per second.

When the race car moves : Now the circles are not concentic anymore  and the observer in the front of the car will receive more waves per second (frequency received higher). Conversely the observer behind the car will receive fewer waves per second (frequency received is lower)                                                                       

The Frequency Doppler Effect also occurs when the observer approaches or moves 

If the observer approaches the source with the velocity vp, then the observer will receive more waves so that its frequency is higher. The formula for the frequency is : 

f’ = {(ν +ν_p)/ν}f

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