Let’s look at the Doppler effect for the case of sound waves:
10.1.2 Construct wavefront diagrams for moving-detector and moving source situations
10.1.3 Derive the equations for the Doppler effect for sound in the cases of a moving detector and a moving source.
First lets look at the case of a moving source and stationary observer.
Now the frequency measured by the observer is:
Do a little algebra and we get the formula given in the IB formula booklet:
The plus/minus has been added to compensate for the direct of the source. The sign should be negative if the source is approaching the observer and positive if the source is moving away from the observer.
Now for a stationary source and a moving observer:
You may ask why would it be different if the observer or the source moves? After all motion is relative, and it is, but the speed of sound is fixed relative to the medium (air) that it is traveling in, this causes differences…
The wavelength is speed of sound divided by the frequency, we can then rewrite the equation as:
This last equation is given in the IB formula booklet. The plus or minus is added to compensate for the direction of the observer. The sign should be negative if the observer is approaching the source and positive if the observer is moving away from the source.
Examples: The fundamental frequency of a train whistle is 300 Hz, and the speed of the train is 60 km/h. On a day
