The Doppler Effect

By Oleksandr Koliakin

You may have heard of the Doppler Effect, but do you know what it is? The Doppler Effect is an effect that can be observed on any types of waves, including sound and light. Here is a classical example of how the Doppler Effect works:

When an ambulance or any vehicle that emits loud sounds approaches you, you may notice that its sound sounds very high pitched. When it passes by, and moves away from you, you might notice that the sound becomes very low-pitched.

This is because when a source of sound is coming towards you, the sound waves ‘bunch up’ together, which means that their wavelength decreases, therefore the pitch increases. When the ambulance passes by, the sound waves behind it are spread further apart than if it was stationary, so you hear a low-pitched sound. You might notice that if there is a stationary source of sound, its pitch doesn’t change, no matter where you stand.

The equation for the Doppler Effect is:

Where c is the speed of sound (or light), v0 is the velocity at which an observer is moving towards the source of frequency fs, which is itself moving towards the observer at velocity vs. f0 is the observed frequency. The speed of sound is approximately 331.45 m/s. If the source of sound is moving away from you, or you are moving away from it, make sure that the value for your or the source’s speed is negative.


- Sciencia (book)

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