Doppler Effect and Beats

Also called

Doppler effect · Doppler shift · apparent frequency · moving source · moving observer · ambulance siren · siren pitch · beats · beat frequency · tuning forks · superposition · red shift · blue shift · expanding universe · wavefronts · pitch · डॉप्लर प्रभाव · विस्पंद · अभिरक्त विस्थापन

Topics

• The Doppler effect: the frequency heard changes when the source or the listener moves; the emitted frequency does not.
• A source moving towards you bunches its wavefronts: shorter wavelength, higher pitch, f′ = f v/(v − vₛ).
• Once it has passed, the wavefronts behind it are stretched: lower pitch, f′ = f v/(v + vₛ).
• A listener walking towards a still source meets crests more often: f′ = f (v + vₒ)/v; walking away, fewer.
• Two sounds of nearly equal frequency add to a wave whose loudness waxes and wanes: beats.
• The beat frequency is the difference of the two frequencies, |f₁ − f₂|; musicians tune by making it zero.
• Light from a receding galaxy is stretched to longer wavelengths: its spectral lines move towards the red.
• Distant galaxies show larger red shifts, so they recede faster the farther they are: the universe is expanding.

About this model

A GLB file of about 493 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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