Waves & Sound · Physics

Doppler Effect Simulation

Drive a siren past a microphone and watch the wavefronts bunch up ahead and spread out behind it. Hear the pitch drop and push the source past the speed of sound.

Interactive virtual lab · no download · works on phones and laptops

Chapter: Waves
For: Class 11 · JEE · NEET
Time: ~10 min

Doppler Effect is a Pro simulation

Pro opens all 125 virtual labs — 483 simulations with guides and quizzes.

How to use it

1Set the source speed and frequency.
2Move the listener or drag the microphone off the road.
3Switch on the sound to hear the pitch.
4Watch the frequency-against-time graph.

What to notice

f' = f(v + v₀)/(v − vₛ) along the line of sight.
Ahead of a moving source the wavelength is (v − vₛ)/f: higher pitch.
The pitch drops as the source passes.
Faster than sound, the fronts form a Mach cone of half-angle sin⁻¹(v/vₛ).

For teachers

A ready-made teaching kit comes with this lab

Lesson plan
18 min, 4 steps
Ask the class
4 questions with answers
Quick quiz
5 questions, printable
Key formulas
3 formulas

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About the Doppler Effect simulation

When a source of sound moves towards you, each wave crest is emitted a little closer than the last, so the crests arrive more often: you hear a higher pitch. As it moves away the pitch drops. A moving listener also meets the crests more or less often. This is the Doppler effect, and it is why a passing ambulance's siren seems to fall in pitch.

This Doppler effect simulation draws the wavefronts as they spread from a moving siren, computes the frequency heard at a microphone you can move, plots it against time and can play it as sound. Push the source past 340 m/s to see the fronts pile into a Mach cone.

Also covers: apparent frequency, moving source, moving observer, sonic boom, mach cone, siren pitch.

Frequently asked questions

What is the Doppler effect formula for sound?

f' = f(v + v₀)/(v − vₛ), with v₀ and vₛ positive when the listener and source move towards each other.

Why does the pitch of a siren drop as it passes?

Approaching, the crests are squeezed together (shorter wavelength, higher frequency); receding, they are stretched out.

What is a sonic boom?

When the source moves faster than sound, the wavefronts pile up on a cone (the Mach cone). Its arrival is heard as a sudden boom.

Does the Doppler effect depend on the distance?

No — only on the velocity components along the line joining source and listener, which is why the pitch changes most quickly as the source passes closest.