Doppler Effect is a free interactive simulation of the Doppler effect for GCSE Physics (Edexcel IGCSE 4PH1). Students vary the speed of a moving wave source and compare the wavefront pattern and oscilloscope readout at two observers to investigate how motion changes frequency and wavelength. No login required — includes a worksheet and self-marking quiz.
Aim: To investigate how the motion of a wave source affects the observed frequency and wavelength of the waves it emits.
Source speed
Playback
What variables could you change in this simulation, and which are you keeping
constant?
Set the source to Stationary and sketch the wavefront pattern.
Now set it to Medium. How does the spacing between wavefronts
differ in front of and behind the moving source, compared to when it was
stationary?
Observer B is in the path of the approaching source. Describe how the wavefronts
reach Observer B compared to Observer A. What does this suggest about the
frequency each of them detects?
Change the source speed to Fast and compare the wavefront
pattern with Slow. What does this tell you about how source
speed affects the Doppler effect?
Turn on Show Readout. Describe the difference between the two
oscilloscope traces at Observer A and Observer B. What does this confirm about
the frequency each observer detects?
Predict: if the source moved at exactly the same speed as the waves, what would
the wavefront pattern look like in front of it?
The Doppler effect also applies to light — stars moving away from Earth show a
red shift in their spectrum. Using what you have observed, explain why a
receding source produces a lower-frequency (longer-wavelength) signal, and why an
ambulance siren sounds higher-pitched as it approaches you and lower-pitched as it
passes and moves away.