Most people have heard a siren passing by, only to hear a shift in the frequency of the siren. It's not because the siren is changing, rather, there is motion involved - between the siren and the hearer.
If there is relative motion between a source that produces a sound and the observer that hears the sound there will be a shift in frequency as perceived by the observer. This shift is referred to as a Doppler shift.
If there is relative motion between a source that produces a sound and the observer that hears the sound there will be a shift in frequency as perceived by the observer. This shift is referred to as a Doppler shift.
This video examines an animation that demonstrates the Doppler shift in action. What do you notice?
You should observe that there is a reduction of the wavelength if there is relative motion of the observer TOWARDS the source.
This results in an increased perceived frequency.
Similarly there is an increase of the wavelength if there is relative motion of the observer AWAY from the source.
This results in a decreased perceived frequency.
This results in an increased perceived frequency.
Similarly there is an increase of the wavelength if there is relative motion of the observer AWAY from the source.
This results in a decreased perceived frequency.
ââNow that we have a conceptual understanding of the Doppler shift, we now need to look at the mathematical modelling that relates the frequency with the relative velocity between source and observer.
Watch this video examines the mathematical model.
Sample Problem
We are now ready at looking at a sample problem. Have a go at attempting the problem before watching the explanation video
We are now ready at looking at a sample problem. Have a go at attempting the problem before watching the explanation video
Worksheet
A Doppler effect worksheet for you to download and try
A Doppler effect worksheet for you to download and try
Interactive
Lets look at more closely
In the following interactive, by Tom Walsh
Lets look at more closely
In the following interactive, by Tom Walsh
- Set the sliders to adjust the speed of the sound source and the sound observer.
- Use the buttons to start or reset and to turn the sound on and off.
- Examine the effect of the relative motion on the wavelength received by the observer.
Extension
Although not part of a standard high school course, its helpful to see how the Doppler effect formula is derived, so I show you here
Although not part of a standard high school course, its helpful to see how the Doppler effect formula is derived, so I show you here
This is a great demonstration in the classroom. Use a long sock (like a ski sock), and play a mono-frequency sound on your phone. Place the phone in the sock, whilst playing the sound, and the spin it around your head